Obesity a cause of breast cancer?

Yes, obesity is a well-established risk factor for breast cancer, particularly after menopause. Excess body fat influences breast cancer risk through several biological mechanisms:

1. Increased Estrogen Production

• Fat tissue is a significant source of estrogen in postmenopausal women. Higher levels of estrogen can promote the development of hormone receptor-positive breast cancers.

2. Inflammation

• Obesity is associated with chronic low-grade inflammation, which can damage DNA and promote tumor growth.

3. Insulin Resistance and High Insulin Levels

• Obesity often leads to insulin resistance and higher levels of insulin in the blood, which may promote cancer development by stimulating cell division and reducing cell death.

4. Adipokines

• Fat cells release adipokines, such as leptin, which can promote tumor growth, while reducing adiponectin, a hormone that has protective effects against cancer.

5. Increased Oxidative Stress

• Excess fat contributes to higher levels of oxidative stress, which can lead to DNA damage and cancer.

6. Lifestyle Factors

• Obesity is often associated with lifestyle factors such as physical inactivity and poor diet, which can further increase breast cancer risk.

Evidence

Numerous studies and meta-analyses show a clear link between obesity and increased breast cancer risk, especially for:

• Postmenopausal women: The risk is higher in postmenopausal women because their primary source of estrogen is fat tissue.
• Certain subtypes of breast cancer: Hormone receptor-positive breast cancers are particularly influenced by obesity.

Prevention

Maintaining a healthy weight through a balanced diet and regular physical activity is an effective strategy to reduce the risk of breast cancer and improve overall health.

Author:Emily Johnson

Obesity is being reported as the greatest avoidable factor in breast cancer, but is this really what the study says?

The researchers at the University of Oxford performed a meta-analysis, a study that combines the results of several previously completed studies on 13 published studies, combining data on 6,000 women.

However, they did not analyse data on women who developed cancer; rather, they investigated whether obesity and other lifestyle factors were related to levels of circulating sex hormones – which in turn are linked to cancer risk. Breast cancer in postmenopausal women has been shown to be associated with levels of sex hormones (e.g. testosterone and oestrogen). But not all breast cancers are linked with these hormones; in premenopausal women, there is a natural variation in the levels of sex hormones due to the woman’s menstrual cycle.

Study Results

• The strongest correlation found was a directly positive one between sex hormone levels and women’s BMI scores, that is, higher sex hormone levels are found in those with higher BMIs.
• However, it was also shown that women who smoked 15 or more cigarettes a day also had higher levels of all hormones than non-smokers.
• Similarly, women who drank 20 g (approximately 2.5 units) or more of alcohol a day also had higher levels than non-drinkers.
• Other breast cancer risk factors, such as age of menopause, number of children, age at first pregnancy, or family history, were not shown to be linked to the hormone levels.

The study authors claim their motivation is to understand the mechanism through which these lifestyles factors increase breast cancer risk. Whilst this study adds weight and new information in cannot conclude anything. In particular because it was a cross-sectional study.Cross sectional research observes a series of factors at only a single point in time, thus it cannot tell us how factors are related to each other, or how they vary over time. Thus, for example, the study cannot establish whether a woman’s weight gain causes her hormone levels to rise, or if the raise in hormone levels causes the woman’s weight to rise.

Although this study has been accurately reported the headlines implying that obesity is the largest cause of cancer is overstating the findings and confusing correlation with causation.

This research doesn’t prove that obesity, high levels of alcohol consumption, and smoking directly cause cancer; however, it fully endorses and adds weight to the current advice that avoiding the above lifestyle factors can reduce the risk of cancer, including breast cancer.