Friday, July 29, 2011
Vitamins
Vitamins and minerals are substances that are found in the foods we eat. Your body needs them to work properly, so you grow and develop just like you should. When it comes to vitamins, each one has a special role to play. For example:
- Vitamin D in milk helps your bones.
- Vitamin A in carrots helps you see at night.
- Vitamin C in oranges helps your body heal if you get a cut.
- B vitamins in leafy green vegetables help your body make protein and energy.
Vitamins Hang Out in Water and Fat
There are two types of vitamins: fat-soluble and water-soluble.
When you eat foods that contain fat-soluble vitamins, the vitamins are stored in the fat tissues in your body and in your liver. They wait around in your body fat until your body needs them.
Fat-soluble vitamins are happy to stay stored in your body for a while — some stay for a few days, some for up to 6 months! Then, when it's time for them to be used, special carriers in your body take them to where they're needed. Vitamins A, D, E, and K are all fat-soluble vitamins.
Water-soluble vitamins are different. When you eat foods that have water-soluble vitamins, the vitamins don't get stored as much in your body. Instead, they travel through your bloodstream. Whatever your body doesn't use comes out when you urinate (pee).
So these kinds of vitamins need to be replaced often because they don't stick around! This crowd of vitamins includes vitamin C and the big group of B vitamins — B1 (thiamin), B2 (riboflavin), niacin, B6 (pyridoxine), folic acid, B12 (cobalamin), biotin, and pantothenic acid.
Vitamins Feed Your Needs
Your body is one powerful machine, capable of doing all sorts of things by itself. But when it comes to vitamins, it can use some help. That's where food comes in. Your body is able to get the vitamins it needs from the foods you eat because different foods contain different vitamins. The key is to eat different foods to get an assortment of vitamins. Though some kids take a daily vitamin, most kids don't need one if they're eating a variety of healthy foods.
Now, let's look more closely at vitamins — from A to K:
Vitamin A
This vitamin plays a really big part in eyesight. It's great for night vision, like when you're trick-or-treating on Halloween. Vitamin A helps you see in color, too, from the brightest yellow to the darkest purple. In addition, it helps your body fight infections by boosting your immune system.
Which foods are rich in vitamin A?
- milk fortified with vitamin A
- liver
- orange fruits and vegetables (like cantaloupe, carrots, sweet potatoes)
- dark green leafy vegetables (like kale, collards, spinach)
The Nutrition Source
The Institute of Medicine's current recommended intake of vitamin A is 900 micrograms of retinol for men (equivalent to 3,000 IU) and 700 micrograms of retinol for women (equivalent to 2,333 IU). The upper limit for vitamin A intake from retinol is 3,000 micrograms, but intakes this high may increase the risk of hip fracture or interfere with the beneficial actions of vitamin D.
Food sources: Many breakfast cereals, juices, dairy products, and other foods are fortified with retinol (also known as preformed vitamin A). Many fruits and vegetables, and some supplements, also contain beta-carotene and other vitamin A precursors, which the body can turn into vitamin A. It's best to choose a multivitamin supplement that has all or the vast majority of its vitamin A in the form of beta-carotene.
Vitamin A does much more than help you see in the dark. It stimulates the production and activity of white blood cells, takes part in remodeling bone, helps maintain the health of endothelial cells (those lining the body's interior surfaces), and regulates cell growth and division. This latter role had researchers exploring for years the relationship between vitamin A and cancer. Specifically, researchers looked at whether people could reduce their cancer risk by taking supplements of beta-carotene, one of several precursor compounds that the body can transform into vitamin A, or by taking the active form of vitamin A (also called retinol or preformed vitamin A). Several studies and randomized trials have dashed this hypothesis.
Although it's possible to get too little vitamin A, it's easy to get too much preformed vitamin A (retinol) from supplements. Intake of up to 3,000 micrograms of preformed vitamin A, more than three times the current recommended daily level, is thought to be safe. However, there is some evidence that this much preformed vitamin A might increase the risk of hip fracture or some birth defects. Another reason to avoid too much preformed vitamin A is that it may interfere with the beneficial actions of vitamin D.
In contrast to preformed vitamin A, beta-carotene is not toxic even at high levels of intake. The body can form vitamin A from beta-carotene as needed, and there is no need to monitor intake levels, as there is with preformed vitamin A. Therefore, it is preferable to choose a multivitamin supplement that has all or the vast majority of its vitamin A in the form of beta-carotene; many multivitamin manufacturers have already reduced the amount of preformed vitamin A in their products. Smokers should avoid high-dose single supplements of beta-carotene, since some randomized trials in smokers have linked high dose supplementation with increased lung cancer risk
The B Vitamins
There's more than one B vitamin. Here's the list: B1, B2, B6, B12, niacin, folic acid, biotin, and pantothenic acid. Whew — that's quite a group!
The B vitamins are important in metabolic (say: meh-tuh-bah-lik) activity — this means that they help make energy and set it free when your body needs it. So the next time you're running to third base, thank those B vitamins.
This group of vitamins is also involved in making red blood cells, which carry oxygen throughout your body. Every part of your body needs oxygen to work properly, so these B vitamins have a really important job.
Which foods are rich in vitamin B?
- whole grains, such as wheat and oats
- fish and seafood
- poultry and meats
- eggs
- dairy products, like milk and yogurt
- leafy green vegetables
- beans and peas
Three of the B Vitamins: Folate, Vitamin B6, and Vitamin B12
Introduction
One of the advances that changed the way we look at vitamins was the discovery that too little folate, one of the eight B vitamins, is linked to birth defects such as spina bifida and anencephaly.
The Institute of Medicine's recommended intake of folate (also called vitamin B9) is 400 micrograms per day. () The upper limit of intake for adults is set at 1,000 micrograms per day of folic acid from fortified food or as a supplement, not including folate from food. People who regularly drink alcohol should make sure to get at least 600 micrograms of folate a day. It is best to achieve that level of intake through a healthy diet; taking a standard multivitamin (which contains 400 micrograms of folic acid) is added insurance. People should avoid taking higher doses of folic acid supplements.
Fifty years ago, no one knew what caused these birth defects, which occur when the early development of tissues that eventually become the spinal cord, the tissues that surround it, or the brain goes awry. More than three decades ago, British researchers found that mothers of children with spina bifida had low vitamin levels. Eventually, two large trials in which women were randomly assigned to take folic acid (the form of folate added to multivitamins or fortified foods) or a placebo showed that getting too little folate increased a woman's chances of having a baby with spina bifida or anencephaly and that getting enough folate could greatly reduce the incidence of these birth defects.
Timing of folate is critical: For folate to be effective, it must be taken in the first few weeks after conception, often before a woman knows she is pregnant.
Since the advent of mandatory folic acid fortification in 1998, neural tube birth defects have dropped by 20 to 30 percent, and studies have shown that far fewer people have low levels of folate in their blood.
Another line of research about folate and two other B vitamins, vitamin B6 and vitamin B12, explores their roles in fighting heart disease and some types of cancer. The research findings have been mixed, to date. While some studies suggest that these three vitamins can lower the risk of these chronic diseases, some studies do not. And now, more than a decade after the start of mandatory fortification in the U.S., there’s been a heated debate about the possible risks from getting too much folic acid. Overall, the evidence suggests that the amount of folic acid in a typical multivitamin does not cause any harm—and may help prevent these diseases, especially among people who do not get enough folate through their diets, and among individuals who drink alcohol. (Read more about the folic acid controversy.)
B Vitamins and Heart Disease
The Institute of Medicine's recommended intake of vitamin B6 (also called pyridoxine) is 1.3 to 1.7 milligrams per day, depending on age and gender. Somewhat higher intakes than that may protect against colon cancer, but more research is needed. ) Very high-dose vitamin B6 supplements should be avoided, since they could lead to nerve damage; in light of these concerns, the Institute of Medicine set the upper limit for vitamin B6 intake in adults at 100 milligrams per day (an amount that can only be achieved through high dose supplements).
In 1968, a Boston pathologist investigated the deaths of two children from massive strokes. Both had inherited conditions that caused them to have extremely high levels of a protein breakdown product in their blood, and both had arteries as clogged with cholesterol as those of a 65-year-old fast-food addict. Putting one and one together, he hypothesized that lower, but still elevated levels of this breakdown product—called homocysteine—would contribute to the artery-clogging process of atherosclerosis.
How do B vitamins fit into the homocysteine picture? Folate, vitamin B6, and vitamin B12 play key roles in converting homocysteine into methionine, one of the 20 or so building blocks from which the body builds new proteins. Without enough folate, vitamin B6, and vitamin B12, this conversion process becomes inefficient and homocysteine levels increase. In turn, increasing intake of folate, vitamin B6, and vitamin B12 decreases homocysteine levels.
Since these early observations about homocysteine, most but not all studies have linked high levels of homocysteine with a modest increase in risk of heart disease and stroke. And some but not all observational studies, including the Nurses' Health Study, show lower risks of cardiovascular disease, stroke, and hypertension among people with higher intakes of folate, those who use multivitamin supplements, or those with higher levels of serum folate (the form of folate found in the body). But linking higher homocysteine levels—and lower folate levels—with heart disease risk does not necessarily mean that lowering homocysteine by taking folate and other B vitamins will lower risk. Ideally, this would be tested in randomized trials.
Several large randomized trials of B vitamins to lower homocysteine and prevent heart disease and stroke have failed to find any benefit. These trials had similar designs: Adults who had a history of heart disease or stroke, or who were at a very high risk of heart disease were given a pill containing high doses of vitamins B6, B12, and folic acid or a placebo. The studies found that taking high doses of the three B vitamins lowered homocysteine levels but did not lead to a reduction in coronary heart events.
But looking at cardiovascular disease as a whole may have obscured a potential benefit of at least one of the B vitamins, and studying people who already have advanced vascular disease may be too late in the process: The most recent analysis of multiple studies suggests that folic acid supplements can reduce the risk of stroke in people who have not already suffered a stroke, but they do not reduce the risk of second stroke in people who have already had one. Folic acid supplements were most protective in studies that lasted at least three years and that combined folic acid with vitamins B6 and B12. Trials that enrolled more men than women also showed more of a benefit, perhaps because men are at higher risk of stroke in general.
Enough folate, at least 400 micrograms a day, isn't always easy to get from food that is not fortified. That's why women of childbearing age are urged to take extra folic acid as a supplement. It's also why the US Food and Drug Administration now requires that folic acid be added to most enriched breads, flour, cornmeal, pastas, rice, and other grain products, along with the iron and other micronutrients that have been added for years.
Food sources: Vitamin B12 is found naturally in animal products (such as fish, poultry, meat, eggs, or dairy); it is also found in fortified breakfast cereals and enriched soy or rice milk. Most people have plenty of vitamin B12 in their diets. The main concern is whether vitamin B12 is adequately absorbed. Read more about vitamin B12 deficiency.
More evidence on folate's possible benefits comes from a study on stroke rates before and after mandatory folic acid fortification. The U.S. and Canada have seen stroke death rates fall more rapidly after fortification than they did before fortification; the U.K., which does not yet require folic acid fortification, saw no such change in stroke death rates.
While several trials of B vitamins and heart disease have yet to report results , the current weight of the evidence suggests that there may be no benefit to B vitamin supplementation in people who already have heart disease—and who are already taking the world’s best medicines to control it. To date, no one has conducted a randomized controlled trial of folic acid supplementation and heart disease in healthy people, probably because it would take decades to yield results and would be very costly.
Ultimately, folic acid supplementation may only reduce the risk of heart disease in people who have lower levels of folate intake, most likely in countries that do not fortify their food supply with folic acid. In people who already get enough folate in their diets, further supplementation with high doses of folic acid supplements—much higher than what is found in a standard multivitamin—has not been found to be beneficial and might actually cause harm.
Folate and Cancer
In addition to converting homocysteine to methionine, folate plays a key role in building DNA, the complex compound that forms our genetic blueprint. Observational studies show that people who get higher than average amounts of folate from their diets or folic acid supplements for 15 years or more have lower risks of colon cancer and breast cancer. This could be especially important for those who drink alcohol, since alcohol interferes with the proper metabolism of folate and inactivates circulating folate. An interesting observation from the Nurses' Health Study is that higher intake of folate appears to blunt the increased risk of breast cancer seen among women who have more than one alcoholic drink a day. More recent studies have had similar findings, including one from Sweden that found that sufficient folate intake can protect against breast cancer even in women who have only one drink a day or less.
But the relationship between folate and cancer is a complicated one, especially for people at a high risk of colon cancer. Colorectal adenomas, or polyps, are pre-cancerous growths in the large intestine. A recent multiyear trial looked at whether high-dose folic acid supplements could prevent new polyps in people who had a history of polyps. The study found that taking a daily pill with 1,000 micrograms of folic acid offered no protection against new polyps, and, more worrisome, increased the risk of developing multiple or more serious polyps.
In the U.S., fortification itself has increased people’s daily folic acid intake, and one highly publicized study suggested that folic acid fortification might have caused a small increase in the incidence of colon cancer. There’s another equally plausible explanation for the increase—greater detection of existing tumors in the colon and rectum due to more widespread use of colonoscopy. The steady decline in deaths from colon cancer before and after the onset of folic acid fortification suggests that screening, not folic acid fortification, is responsible for the uptick in colon cancer rates. The overall evidence from studies in humans shows a lower risk of colon and breast cancer with greater intake of folate or folic acid, rather than increased risk. )Keep in mind that this study tested a high dose of folic acid, more than two times higher than what is found in a standard multivitamin; furthermore, study participants were already at a very high risk of developing new polyps. This may be another case where timing of folate intake is critical: Getting adequate folate may prevent polyps in people who do not have them, but high dose folic acid supplements may speed up polyp growth in people who do. And it is reassuring that other trials of high dose B vitamin supplementation, such as the Women's Antioxidant and Folic Acid Cardiovascular Study, have not found higher rates of cancer in supplement users.
When teasing out the relationship between any vitamin supplement and cancer, it is important to remember that cancer cells are essentially our own cells on overdrive, growing and rapidly dividing, and they have a greater need for nutrients than most of our normal cells do. Studies done decades ago show that folate is needed for tumor cell growth. Indeed, one successful chemotherapy agent works as a folate antagonist, since rapidly dividing cells require folate to maintain their fast pace of cell division. So for people who have cancer or precancerous growths, nutritional supplements may be a double-edged sword. If you have cancer, make sure to check with your doctor before beginning any vitamin supplement regimen.
The Bottom Line: Getting Your B Vitamins from Diet—and a Daily Multivitamin
The definition of a healthy daily intake of B vitamins isn't set in stone, and it is likely to change over the next few years as data from ongoing randomized trials are evaluated. In the U.S., folic acid fortification of food has increased the percentage of adults who have adequate levels of folate in their blood. Yet still, only a fraction of U.S. adults currently get the recommended daily intake of all B vitamins by diet alone. If you are concerned about getting too much folic acid, keep the multivitamin, but skip the energy bars, cold breakfast cereals, and other processed foods that are heavily fortified with folic acid.
Vitamin C
This vitamin is important for keeping body tissues, such as gums and muscles in good shape. C is also key if you get a cut or wound because it helps you heal.
This vitamin also helps your body resist infection. This means that even though you can't always avoid getting sick, vitamin C makes it a little harder for your body to become infected with an illness.
Which foods are rich in vitamin C?
- citrus fruits, like oranges
- cantaloupe
- strawberries
- tomatoes
- broccoli
- cabbage
- kiwi fruit
- sweet red peppers
Vitamin C
The Institute of Medicine's current recommended dietary intake for vitamin C (also called ascorbic acid) is 90 milligrams for men and 75 milligrams for women (add an extra 35 milligrams for smokers). The upper limit for vitamin C is set at 2 grams per day.
There's no good evidence that megadoses of vitamin C improve health. As the evidence continues to unfold, 200 to 300 milligrams of vitamin C a day appears to be a good target. This is easy to hit with a good diet and a standard multivitamin.
Food sources: Excellent food sources of vitamin C are citrus fruits or citrus juices, berries, green and red peppers, tomatoes, broccoli, and spinach. Many breakfast cereals are also fortified with vitamin C.
Vitamin C has been in the public eye for a long time. Even before its discovery in 1932, nutrition experts recognized that something in citrus fruits could prevent scurvy, a disease that killed as many as two million sailors between 1500 and 1800. In the 1970s, Chemistry and Peace Nobel laureate Linus Pauling promoted daily megadoses of vitamin C (the amount in 12 to 24 oranges) as a way to prevent colds and some chronic diseases.
There's no question that vitamin C plays a role in controlling infections. It's also a powerful antioxidant that can neutralize harmful free radicals, and it helps make collagen, a tissue needed for healthy bones, teeth, gums, and blood vessels. The question is, do you need lots of vitamin C to keep you healthy?
No. Vitamin C's cold-fighting potential certainly hasn't panned out. Small trials suggest that the amount of vitamin C in a typical multivitamin taken at the start of a cold might ease symptoms, but for the average person, there's no evidence that megadoses make a difference, or that they prevent colds. Studies of vitamin C supplements and heart disease, cancer, and eye diseases such as cataract and macular degeneration also show no clear patterns.
Vitamin D
No bones about it . . . vitamin D is the vitamin you need for strong bones! It's also great for forming strong teeth. Vitamin D even lends a hand to an important mineral — it helps your body absorb the amount of calcium it needs. Vitamin D is made in the skin when exposed to sunlight, or you can get it from the foods you eat.
Which foods are rich in vitamin D?
- milk fortified with vitamin D
- fish
- egg yolks
- liver
- fortified cereal
Vitamin D and Health
Low Vitamin D: A Global Concern
The Institute of Medicine's (IOM) recommended daily intake of vitamin D is 600 IU for people ages 1 to 70, and 800 IU after age 70. Yet this recommendation is overly conservative, since the best available evidence shows optimal intakes are higher, at least 800–1,000 IU for adults.
In extremely high doses—hundreds of thousands of IU or more—vitamin D is toxic and can even cause death. But the new guidelines from the IOM note that in children over the age of 9 and in adults, taking up to 4,000 IU per day as a supplement is safe. For children ages 4 to 8, up to 3,000 IU per day is considered safe, and for children ages 1 to 3, 2,500 IU; in older infants (6 to 12 months), up to 1,500 IU per day is considered safe, and in young infants (0 to 6 months), up to 1,000 IU.
Some people may need 2,000 IU per day (or more) for adequate blood levels, particularly if they have darker skin, spend winters at higher latitudes (such as the northern U.S.), or spend little time in the sun. If you fall into one of these groups, ask your doctor about ordering a vitamin D blood test.
To prevent rickets, the American Academy of Pediatrics (AAP) recommends vitamin D supplements of 400 IU per day for breastfed infants, and also for non-breastfed infants and children who do not drink at least a liter of vitamin D fortified milk each day. The IOM also sets intake levels for infants (0 to 12 months) at 400 IU daily.
Infants and children at high risk of deficiency—premature infants, children and infants with dark skin, or who live at high latitudes—may need supplements of up to 800 IU per day, especially in the winter, according to the AAP.
If you live north of the line connecting San Francisco to Philadelphia and Athens to Beijing, odds are that you don't get enough vitamin D. The same holds true if you don't get outside for at least a 15-minute daily walk in the sun. African-Americans and others with dark skin, as well as older individuals, tend to have much lower levels of vitamin D, as do people who are overweight or obese.
Worldwide, inadequate vitamin D is common, and deficiencies can be found on all continents, in all ethnic groups, and across all ages. Some surveys suggest that perhaps half of the world’s population has inadequate blood levels of vitamin D. ) Indeed, in industrialized countries, doctors are even seeing the resurgence of rickets, the bone-weakening disease that had been largely eradicated through vitamin D fortification.
Why are these widespread low levels of vitamin D such a great concern? Because research conducted over the past decade suggests that vitamin D plays a much broader disease-fighting role than once thought.
Being “D-ficient” may increase the risk of a host of chronic diseases, such as , , , and multiple sclerosis, as well as , such as and even the .
Currently, there’s scientific debate about how much vitamin D people need each day. The Institute of Medicine (IOM), in a long-awaited report released in November 2010 recommends increasing the daily vitamin D intake for children and adults in the U.S. and Canada, to 600 IU per day for people ages 1 to 70, and 800 IU for people over age 70. The report also recognized the safety of vitamin D by increasing the upper limit from 2,000 to 4,000 IU per day, and acknowledged that even at 4,000 IU per day, there was no good evidence of harm.
The new guidelines, however, are overly conservative about the recommended intake, and they do not give enough weight to some of the latest science on vitamin D and health. For bone health and chronic disease prevention, many people are likely to need more vitamin D than even these new government guidelines recommend.
Vitamin D Sources and Function
Vitamin D is both a nutrient we eat and a hormone our bodies make. Few , so the biggest dietary sources of vitamin D are fortified foods and .
Very few foods naturally contain vitamin D. Good sources include dairy products and breakfast cereals (both of which are fortified with vitamin D), and fatty fish such as salmon and tuna.
For most people, the best way to get enough vitamin D is taking a supplement, but the level in most multivitamins (400 IU) is too low. Encouragingly, some manufacturers have begun adding 800 or 1,000 IU of vitamin D to their standard multivitamin preparations. If the multivitamin you take does not have 800 or 1,000 IU of vitamin D, you may want to consider adding a separate vitamin D supplement, especially if you don't spend much time in the sun. Talk to your healthcare provider.
The body also manufactures vitamin D from cholesterol, through a process triggered by the action of sunlight on skin, hence its nickname, “the sunshine vitamin.” Yet many people do not make enough , among them, people who have a darker skin tone, who are overweight, who are older, and who cover up when they are in the sun.
Correctly applied sunscreen reduces our ability to absorb vitamin D by more than 90 percent. And not all sunlight is created equal: The sun’s ultraviolet B (UVB) rays—the so-called “tanning” rays, and the rays that trigger the skin to produce vitamin D—are stronger near the equator and weaker at higher latitudes. So in the fall and winter, people who live at higher latitudes (in the northern U.S. and Europe, for example) can’t make much if any vitamin D from the sun.
Vitamin D helps ensure that the body absorbs and retains calcium and phosphorus, both critical for building bone. Laboratory studies show that vitamin D can reduce cancer cell growth, can increase muscle strength and reduce falls in older people, and plays a critical role in controlling infections. Many of the body’s organs and tissues have receptors for vitamin D, and scientists are still teasing out its other possible functions.
New Vitamin D Research: Beyond Building Bones
Several promising areas of vitamin D research look far beyond vitamin D’s role in building bones. And, as you might expect, the news media release a flurry of reports every time another study links vitamin D to some new ailment. These reports can be confusing, however, because some studies are stronger than others, and any report needs to be interpreted in the light of all other evidence. More answers may come from randomized trials, such as the (VITAL), which will enroll 20,000 healthy men and women to see if taking 2,000 IU of vitamin D or 1,000 mg of fish oil daily lowers the risk of cancer, heart disease, and stroke.
Here, we provide an overview of some of the more promising areas of vitamin D research, highlighting the complex role of vitamin D in disease prevention—and the many unanswered questions that remain.
Vitamin D and Bone and Muscle Strength
Vitamin D plays a definite role in bone health and reducing fractures; the central issue is, what is the minimum dose that is effective? Several randomized trials have shown that vitamin D supplementation prevents fractures—as long as it is taken in a high enough dose.
Why to Avoid Super High Doses of Vitamin D
A recent vitamin D trial drew headlines for its unexpected finding that a veryhigh dose of vitamin D increased fracture and fall risk in older women. The trial’s vitamin D dose—500,000 IU taken by mouth on a single day, once a year—was much higher than previously tested in an annual regimen.
There’s strong evidence that more moderate doses of vitamin D taken daily or weekly protect against fractures and falls—and are safe. Read more about this study's findings, and why it makes sense to stick to more moderate vitamin D doses and avoid single, super high doses.
A summary of the evidence comes from a combined analysis of 12 fracture prevention trials that included more than 40,000 elderly people, most of them women. Researchers found that high intakes of vitamin D supplements—of about 800 IU per day—reduced hip and non-spine fractures by over 20 percent, while lower intakes (400 IU or less) failed to offer any fracture prevention benefit.
Vitamin D may also help increase muscle strength, which in turn helps to prevent falls, a common problem that leads to substantial disability and death in older people. Once again, vitamin D dose matters: A combined analysis of multiple studies found that taking 700 to 1,000 IU of vitamin D per day lowered the risk of falls by 19 percent, but taking 200 to 600 IU per day did not offer any such protection.
Based on these fall- and fracture-prevention findings, the International Osteoporosis Foundation recommends that adults over age 60 aim for vitamin D blood levels of 30 ng/ml. Most people will need vitamin D supplements of at least 800 to 1,000 IU per day, and possibly higher, to reach these levels.
Vitamin D and Heart Disease
The heart is basically a large muscle, and like skeletal muscle, it has receptors for vitamin D. So perhaps it’s no surprise that studies are finding that inadequate vitamin D may be linked to heart disease. The Health Professional Follow-Up Study checked the vitamin D blood levels in nearly 50,000 men who were healthy, and then followed them for 10 years. They found that men who were low in vitamin D were twice as likely to have a heart attack as men who had adequate levels of vitamin D. Other studies have found that low vitamin D levels were associated with higher risk of heart failure, sudden cardiac death, stroke, overall cardiovascular disease, and cardiovascular death. How exactly might vitamin D help prevent heart disease? There’s evidence that vitamin D plays a role in controlling blood pressure and preventing artery damage, and this may explain these findings. Still, more research is needed before we can be confident of these benefits.
Vitamin D and Cancer
: People who lived at higher latitudes, such as in the northern U.S., had higher rates of death from colon cancer than people who live closer to the equator. The sun’s UVB rays are weaker at higher latitudes, and in turn, people’s vitamin D levels in these high latitude locales tend to be lower. This led to the hypothesis that low vitamin D levels might somehow increase colon cancer risk.
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Since then, dozens of studies suggest an association between low vitamin D levels and increased risks of colon and other cancers. The evidence is strongest for colorectal cancer, with observational studies consistently finding that the lower the vitamin D levels, the higher the risk is of these diseases. Vitamin D levels may also predict cancer survival, but evidence for this is still limited. Yet finding such associations does not necessarily mean that taking vitamin D supplements will lower cancer risk.
The trial will look specifically at whether vitamin D supplements lower cancer risk. It will be years, though, before it releases any results. It could also fail to detect a real benefit of vitamin D, for several reasons: If people in the placebo group decide on their own to take vitamin D supplements, that could minimize any differences between the placebo group and the supplement group; the study may not follow participants for a long enough time to show a cancer prevention benefit; or study participants may be starting supplements too late in life to lower their cancer risk. In the meantime, based on the evidence to date, 16 scientists have circulated a “call for action” on vitamin D and cancer prevention: Given the high rates of vitamin D inadequacy in North America, the strong evidence for reduction of osteoporosis and fractures, the potential cancer-fighting benefits of vitamin D, and the low risk of vitamin D supplementation, they recommend widespread vitamin D supplementation of 2,000 IU per day. The Canadian Cancer Society has also recommended that Canadian adults consider taking vitamin D supplements of 1,000 IU per day during the fall and winter; people who are at high risk of having low vitamin D levels (because they are older, have dark skin, spend little time in the sun, or cover up when they go outside) should consider taking supplements year round.Nearly 30 years ago, researchers noticed an intriguing relati
Vitamin D and Immune Function
Vitamin D’s role in regulating the immune system has led scientists to explore two parallel research paths: Does low vitamin D contribute to the development of multiple sclerosis, type 1 diabetes, and other so-called “autoimmune” diseases, where the body’s immune system attacks its own organs and tissues? And could vitamin D supplements help boost our body’s defenses to fight infectious disease, such as tuberculosis and seasonal flu? This is a hot research area and more findings will be emerging.
Vitamin D and Multiple Sclerosis: Multiple sclerosis (MS) rates are much higher far north (or far south) of the equator than in sunnier climes, and researchers suspect that chronic vitamin D inadequacy may be one reason why. One prospective study to look at this question found that among white men and women, those with the highest vitamin D blood levels had a 62 percent lower risk of developing MS than those with the lowest vitamin D levels. The study didn’t find this effect among black men and women, most likely because there were fewer black study participants and most of them had low vitamin D levels, making it harder to find any link between vitamin D and MS if one exists.
Vitamin D and Type 1 Diabetes: Type 1 diabetes is another disease that varies with geography—a child in Finland is about 400 times more likely to develop it than a child in Venezuela. Evidence that vitamin D may play a role in preventing type 1 diabetes comes from a 30-year study that followed more than 10,000 Finnish children from birth: Children who regularly received vitamin D supplements during infancy had a nearly 90 percent lower risk of developing type 1 diabetes than those who did not receive supplements. Other European case-control studies, when analyzed together, also suggest that vitamin D may help protect against type 1 diabetes. No randomized controlled trials have tested this notion, and it is not clear that they would be possible to conduct.
Vitamin D, the Flu, and the Common Cold: The flu virus wreaks the most havoc in the winter, abating in the summer months. This seasonality led a British doctor to hypothesize that a sunlight-related “seasonal stimulus” triggered influenza outbreaks. More than 20 years after this initial hypothesis, several scientists published a paper suggesting that vitamin D may be the seasonal stimulus. Among the evidence they cite:
- Vitamin D levels are lowest in the winter months.
- The active form of vitamin D tempers the damaging inflammatory response of some white blood cells, while it also boosts immune cells’ production of microbe-fighting proteins.
- Children who have vitamin D-deficiency rickets are more likely to get respiratory infections, while children exposed to sunlight seem to have fewer respiratory infections.
- Adults who have low vitamin D levels are more likely to report having had a recent cough, cold, or upper respiratory tract infection.
A recent randomized controlled trial in Japanese school children tested whether taking daily vitamin D supplements would prevent seasonal flu. The trial followed nearly 340 children for four months during the height of the winter flu season. Half of the study participants received pills that contained 1,200 IU of vitamin D; the other half received placebo pills. Researchers found that type A influenza rates in the vitamin D group were about 40 percent lower than in the placebo group; there was no significant difference in type B influenza rates. This was a small but promising study, and more research is needed before we can definitively say that vitamin D protects against the flu. But don’t skip your flu shot, even if vitamin D has some benefit.
Vitamin D and Tuberculosis: Before the advent of antibiotics, sunlight and sun lamps were part of the standard treatment for tuberculosis (TB). More recent research suggests that the “sunshine vitamin” may be linked to TB risk. Several case-control studies, when analyzed together, suggest that people diagnosed with tuberculosis have lower vitamin D levels than healthy people of similar age and other characteristics. Such studies do not follow individuals over time, so they cannot tell us whether low vitamin D levels led to the increased TB risk or whether taking vitamin D supplements would prevent TB. There are also genetic differences in the receptor that binds vitamin D, and these differences may influence TB risk. Again, more research is needed.
Vitamin D and Risk of Premature Death
A promising report in the Archives of Internal Medicine suggests that taking vitamin D supplements may even reduce overall mortality rates: A combined analysis of multiple studies found that taking modest levels of vitamin D supplements was associated with a statistically significant 7 percent reduction in mortality from any cause. The analysis looked at the findings from 18 randomized controlled trials that enrolled a total of nearly 60,000 study participants; most of the study participants took between 400 and 800 IU of vitamin D per day for an average of five years. Keep in mind that this analysis has several limitations, chief among them the fact that the studies it included were not designed to explore mortality in general, or explore specific causes of death. More research is needed before any broad claims can be made about vitamin D and mortality.
Why the IOM’s Vitamin D Recommendation Falls Short
Taken together, these disparate studies on bone health, heart disease, cancer, immune function, and early death add up to a powerful conclusion: Many people do not get enough vitamin D to protect their bones and minimize risk of falling—and taking vitamin D supplements of 1,000 to 2,000 IU per day would be a safe way to do both. This alone is good reason to consider taking a vitamin D supplement of 1,000 to 2,000 IU per day, and there is a strong likelihood of other benefits, even if not yet proven. Yet the IOM added up the evidence and reached a different conclusion—that children and most adults in the U.S. and Canada only need 600 IU of vitamin D a day. While the report notes that the 600 IU can come from food, supplements, or a combination of both, it acknowledges that very few Americans reach this intake. Despite this, the committee recommended supplements for only a few special groups. There are several reasons why the IOM’s recommendation falls short:
Vitamin E
Everybody needs E. This hard-working vitamin protects your cells and tissues from damage. It is also important for the health of red blood cells.
Which foods are rich in vitamin E?
- whole grains, such as wheat and oats
- wheat germ
- leafy green vegetables
- vegetable oils like sunflower, canola, and olive
- egg yolks
- nuts and seeds
The Institute of Medicine's recommended daily intake of vitamin E (also called alpha- tocopherol) from food now stands at 15 milligrams. That's the equivalent of 22 IU from natural-source vitamin E or 33 IUs of the synthetic form. But researchers are still writing the book on the optimal intake of vitamin E, and the data are sparse and conflicting.
For healthy people, current research suggests that a reasonable level of vitamin E intake may be about 200 IUs of synthetic vitamin E per day, an amount that is difficult to achieve from diet alone; since standard multivitamins usually contain around 30 IU, a separate vitamin E supplement is needed to achieve this level.
For people who already have heart disease and are taking medications to control it, a vitamin E supplement most likely will not offer any additional benefits.
Current guidelines say that consuming more than 1,000 milligrams of supplemental vitamin E per day is not considered safe; that's the equivalent of a supplement with 1,500 IU of natural-source vitamin E or 2,500 IU of synthetic vitamin E.
Food sources: Good sources of vitamin E include sunflower and safflower oils, oil-based salad dressings, almonds, sunflower seeds, peanut butter, and dark leafy greens.
For a time, vitamin E supplements looked like an easy way to prevent heart disease. Promising observational studies, including the Nurses' Health Study and Health Professionals Follow-up Study, suggested 20 to 40 percent reductions in coronary heart disease risk among individuals who took vitamin E supplements (usually containing 400 IU or more) for least two years.
The results of several randomized trials have dampened enthusiasm for vitamin E's ability to prevent heart attacks or deaths from heart disease among individuals with heart disease or those at high risk for it. In the GISSI Prevention Trial, the results were mixed but mostly showed no preventive effects after more than three years of treatment with vitamin E among 11,000 heart attack survivors. Results from the Heart Outcomes Prevention Evaluation (HOPE) trial also showed no benefit of four years worth of vitamin E supplementation among more than 9,500 men and women already diagnosed with heart disease or at high risk for it. Based on these and other studies, the American Heart Association has concluded that "the scientific data do not justify the use of antioxidant vitamin supplements [such as vitamin E] for CVD risk reduction."
A recent scientific analysis raised questions about whether high doses of vitamin E supplements might increase the risk of dying. (7) The authors gathered and re-analyzed data from 19 clinical trials of vitamin E, including the GISSI and HOPE studies; they found a higher rate of death in trials where patients consumed more than 400 IU of supplements per day. While this meta-analysis drew headlines when it was released, there are limitations to the conclusions that can be drawn from it. Some of the findings are based on very small studies; furthermore, many of the high-dose trials of vitamin E included in the analysis were done on people who had chronic diseases, such as heart disease or Alzheimer's disease. So it is not clear that these findings would apply to healthy people.
It's entirely possible that in secondary prevention trials, the use of drugs such as aspirin, beta blockers, and ACE inhibitors mask a modest effect of vitamin E, and that it may have benefits among healthier people. But large randomized controlled trials of vitamin E supplementation in healthy people have yielded mixed results. In the Women's Health Study, which followed 40,000 women for 10 years, vitamin E supplements of 600 IU every other day did not significantly reduce the risk of so-called "major cardiac events" (non fatal heart attack, non-fatal stroke, or cardiovascular death); when these major cardiac events were analyzed separately, however, vitamin E supplementation was linked to a 24 percent lower risk of cardiovascular death. And among women ages 65 and older, vitamin E supplementation reduced the risk of major cardiac events by 26 percent.
The SU.VI.MAX trial, meanwhile, found that seven years of low-dose vitamin E supplementation (as part of a daily antioxidant pill) reduced the risk of cancer and the risk of dying from any cause in men, but did not show these beneficial effects in women; the supplements did not offer any protection against heart disease in men or women. (9) It's possible that vitamin E may have potential benefits in certain subgroups of the general population: A recent trial of vitamin E in Israel, for example, showed a marked reduction in coronary heart disease among people with type 2 diabetes who have a common genetic predisposition for greater oxidative stress.
Vitamin K
Vitamin K is the clotmaster! Remember the last time you got a cut? Your blood did something special called clotting. This is when certain cells in your blood act like glue and stick together at the surface of the cut to help stop the bleeding.
Which foods are rich in vitamin K?
- leafy green vegetables
- dairy products, like milk and yogurt
- broccoli
- soybean oil
Vitamin K helps make four of the 13 proteins needed for blood clotting. Its role in maintaining the clotting cascade is so important that people who take anticoagulants such as warfarin (Coumadin) must be careful to keep their vitamin K intake stable.
Lately, researchers have demonstrated that vitamin K is also involved in building bone. Low levels of circulating vitamin K have been linked with low bone density, and supplementation with vitamin K shows improvements in biochemical measures of bone health. A report from the Nurses' Health Study suggests that women who get at least 110 micrograms of vitamin K a day are 30 percent less likely to break a hip than women who get less than that. Among the nurses, eating a serving of lettuce or other green, leafy vegetable a day cut the risk of hip fracture in half when compared with eating one serving a week. Data from the Framingham Heart Study also shows an association between high vitamin K intake and reduced risk of hip fracture in men and women and increased bone mineral density in women.
People who do not regularly eat a lettuce salad or green, leafy vegetables are likely to be deficient in their intake of vitamin K; national data suggests that only about one in four Americans meets the goal for vitamin K intake from food.
When your body gets this vitamin and the other ones it needs, you'll be feeling A-OK!
Vitamins
A daily multivitamin is a great nutrition insurance policy. Some extra vitamin D may add an extra health boost.
1. Eat a healthy diet. A multivitamin provides some insurance against deficiencies but is far less important for health than the healthy food patterns described on this website. Choose a diet rich in fruits, vegetables, whole grains, nuts and healthy oils, and low in red meat and unhealthy fats—let the Healthy Eating Pyramid be your guide.
2. Choose a daily multivitamin. A daily multivitamin is an inexpensive nutrition insurance policy. Try to take one every day.
3. Think about D. In addition to its bone health benefits, there’s growing evidence that getting some extra vitamin D can help lower the risk of colon and breast cancer. Aim for getting 1,000 to 2,000 IU of vitamin D per day—this likely will require an extra vitamin D pill, in addition to your multivitamin. For more information, see the vitamin D section of The Nutrition Source.
4. Say no to “megas.” In general, avoid mega-dose vitamins and mega-fortified foods. Higher doses of vitamin E may help to prevent heart disease, but in general, the amount in a standard multivitamin is enough to have health benefits. A standard multivitamin also has a day's worth of folic acid, so you should avoid foods that have high amounts of folic acid added to them.Vitamin D is an exception, as many people need more than the RDA.
5. Avoid “super” supplements. Don’t be swayed by the wild health claims of the many health supplements advertised on TV and the Internet. If they sound too good to be true, you can be sure they are. Save your money for healthy food and a good vacation.
Trying to follow all the studies on vitamins and health can make your head swirl. But, when it’s all boiled down, the take–home message is actually pretty simple: A daily multivitamin, and maybe an extra vitamin Dsupplement, is a great way to make sure you’re getting all the nutrients you need to be healthy. The folic acid in most multivitamins helps prevent neural tube defects in newborns; it may lower the risk of heart disease, colon cancer, and breast cancer. Vitamin D from a multivitamin or single supplement can lower the risk of colon and possibly many other cancers.
Of course, there can be too much of a good thing. It’s important not to go overboard with vitamins. While a multivitamin and a vitamin D supplement can help fill some of the gaps in a less than optimal diet, too much can be harmful. In general, stick close to standard recommended doses in a multivitamin. And since your multivitamin will likely contain all the folic acid you'll need, stay away from cereals, protein bars, and other foods that are super-fortified with folic acid.
What about antioxidants for heart attack prevention?
Antioxidants are food supplements that have been promoted as preventing heart disease and stroke. An important early event in the development of a cholesterol plaque in atherosclerosis is the oxidative modification of LDL cholesterol (low density lipoprotein) particles in the blood and the subsequent interaction of this modified LDL with the wall of the coronary artery. This process initiates the formation of the cholesterol plaque.
Antioxidants that block the oxidative modification of LDL have been shown to slow the progression of atherosclerosis in animal experiments. Examples of antioxidants include vitamin E and beta carotene. In humans, observational studies (studies that observe the frequency of related conditions) have found a relationship between the dietary intake of vitamin E and lower rates of heart attacks.
Observational studies provide only circumstantial evidence, however, and credible evidence is obtained only by way of controlled trials (discussed at the beginning of this article). Several controlled trials performed to date have yielded conflicting results on the benefits of antioxidant therapy. These results may possibly be due to the low doses of vitamin E used, the small number of patients in the study, or the limited duration of treatment.
The Heart Outcomes Prevention Evaluation study used a high dose (400 IU per day) of vitamin E over a span of five years in patients with significant risk factors for heart disease or stroke. This study found no difference in the occurrence of heart attack or stroke in the group treated with vitamin E versus those given the placebo. This study demonstrated that antioxidant therapy does not have any benefit in persons who have or are at high risk for having atherosclerosis.