Obesity is a fairly hot topic these days for a variety of health-related reasons. For example, it is known to lead to chronic illnesses including heart disease and diabetes, which are currently reaching epidemic rates in North America. However, obesity is also believed to play a critical role in the development of breast cancer.

Studies have found that the impact of obesity on breast cancer risk is higher in women after menopause. Postmenopausal women who are obese had a higher risk of dying from breast cancer compared with postmenopausal women of lean weight. This is thought to be due to the higher amounts of estrogen that is present in obese women.

Before menopause, the ovaries provide the main source of estrogen for women. However, after menopause, the ovaries stop producing estrogen, and as a result, fat tissue becomes the main estrogen source. Obese women have higher estrogen levels because they have more fat tissue. This means that breast tissue, including breast tumors that are sensitive to estrogen, has the potential to grow more rapidly in the presence of higher estrogen levels.

Even more worrisome, a US study showed that in spite of this increased risk, obese women are less likely to get the screening they need, with mammogram rates below those of healthy weight women. Moreover, breast cancer is often more difficult to detect in obese women than in healthy weight women, and as a result, breast cancer has a tendency to be detected at a later stage in obese women.

Exercise may also have an impact on breast cancer risk. One study, which appeared in the journal Cancer Epidemiology, Biomakers and Prevention, found that women who don't regularly engage in physical activity have more than twice the risk that active women have of developing breast cancer. The combination of inactivity and poor diet packed an even more deadly punch, resulting in almost 5 times the risk of developing breast cancer for postmenopausal women compared to their thinner counterparts. Furthermore, for women who are diagnosed with breast cancer, several studies have supported the benefits of exercise during chemotherapy. Among these were improved physical functioning, higher energy levels, and reduced fatigue, as well as improved overall mood and body esteem.

These studies are just the latest to look at the relationship between weight and breast cancer, both before and after diagnosis. But many more have examined these associations. For example, earlier studies on mice showed that calorie restriction or occasional fasting inhibits breast cancer growth.

While these studies seem to show that controlling calorie intakes plays a role in cancer prevention, researchers also stress the importance of exercise. Why? Well, calorie restriction reduces the amount of insulin-like growth factor (IGF-1) by as much as 70%. IGF-1 helps to regulate aspects of development and aging. Calorie restriction can result in a decrease in bone density, which can lead to osteoporosis. This is a significant health problem in postmenopausal women, as they have an increased risk for breast cancer. Exercise helps to minimize the loss of bone density. Weight-bearing exercise can help build bone strength.

Further dietary studies will emerge, and no doubt we will learn a great deal over the coming years. But for now the message seems to be that weight reduction, exercise, and calorie restriction are important considerations for reducing the risk of breast cancer development.

Written and reviewed by the MediResource Clinical Team