One in eight women will be diagnosed with breast cancer during her lifetime, which makes breast cancer the most commonly diagnosed cancer in women. Each year more than 230,000 women in the Unites States will be diagnosed with breast cancer, and more than 40,000 of these women will die. Although breast cancer is more common in women, about 2,350 men are diagnosed each year, and approximately 440 will die. There are both genetic and environmental risk factors that play a role in developing cancer. One genetic risk is being of old age; 2 out of 3 women with invasive breast cancer are diagnosed after the age of 55. Environment and lifestyle risk factors include being sedentary or lacking physical activity, and being overweight or obese.

Dr. Anne McTiernan has dedicated most of her research to studying these variables, and how they effect the risk of developing breast cancer. Specifically, she studies women who have reached menopausal age and their levels of exercise. McTiernan and other epidemiologists have recognized a link between obesity and increased risk for postmenopausal breast cancer, as well as decreased risk with increased physical activity. Furthermore, many breast cancers are estrogen-sensitive, and therefore researchers think that this hormone may impact the correlation between body fat and risk.

In 2004, Hutch News published an article titled “Regular Exercise Decreases Estrogens.” The article was based on a study performed by Dr. Anne McTiernan and colleagues, which found that three hours of moderate exercise per week significantly reduced circulating estrogens in postmenopausal women. The study examined the differences between women who exercised regularly to women who limit their activity to only stretching. The study targeted postmenopausal women who were sedentary, and overweight or obese at the beginning of the trial. After one year, women who exercised regularly and reduced their body fat by more than two percent also had a 16.7 percent decrease in free serum estradiol, 13.7 percent decrease in serum estradiol, and an 11.9 percent reduction in serum estrone. The active women averaged 171 minutes of exercise per week (almost 3 hours). The findings of this study provide evidence that exercise is an effective way for postmenopausal women to increase their chances of avoiding breast cancer.

Regular Exercise Lowers Estrogens

In 2012, Dr. McTiernan continued her research with colleagues, and performed the first randomized, controlled clinical trial to test the effects of sex hormones in overweight and obese postmenopausal women. This group of women were chosen because they are at a particularly elevated risk of developing breast cancer. The study analyzed data from 439 overweight or obese, sedentary women who are between the ages of 50 and 75. Participants were randomly assigned to one of four groups: exercise only, diet only, exercise and diet, and no intervention. Several forms of sex hormones were measured, including three forms of estrogen, two types of testosterone, androstenedione (a steroid necessary for the production of sex hormones), and sex hormone binding globulin or SHBG (a protein that binds to sex hormones and makes them less active). Elevated levels of SHGB are associated with reduced breast cancer risk. Results from the study revealed significant reduction in hormone levels among women who received dietary weight loss intervention, with the largest reduction in women who both dieted and exercised. Losing as little as five percent of one’s total body weight had a beneficial effect on hormone levels, and the impact increased with the amount of weight loss. This amount of weight loss could cut the risk of developing most estrogen-sensitive breast cancers by 25-50 percent.

Moderate Weight Loss Reduces Levels of Breast Cancer-Linked Hormones

In a very recent study, McTiernan switched her focus on the effects exercise and body fat loss to the effects of vitamin D. An increase in vitamin D lowers estrogen and progesterone levels in women. Researchers analyzed 218 postmenopausal, overweight-to-obese women that had insufficient levels of vitamin D at the beginning of the study. The women were randomly assigned to one of two different groups: a weight loss program plus daily vitamin D3 (2,000 IUs daily) or a weight loss program plus a placebo. The women that received vitamin D supplements took enough to increase their levels to a normal range. At the end of the year-long study, those who took a daily Vitamin-D3 supplement had a significant drop in circulating estrogens. This drop in estrogens was independent of the amount of weight the women lost. This study suggests that vitamin D supplementation may be a safe and practical alternative to estrogen-lowering drugs for overweight and obese women. McTiernan’s past research has provided evidence that exercise and weight loss significant lowers blood estrogens, and this new study suggests that vitamin D (at a normal level) can add to that.

High Blood Levels of Vitamin-D Linked to Reduced Estrogen- and Potentially Lower Breast Cancer Risk

In conclusion, postmenopausal women are at an elevated risk of developing most common types of breast cancer. These women’s risk is increased if they are overweight or obese. There has been a large amount of research that suggests estrogen levels are associated with the risk of developing common types of breast cancer. Research done by Dr. Anne McTiernan and colleagues, provides evidence that lowering body weight, whether it be through diet and/or exercise, and increasing Vitamin-D levels could decrease individual’s estrogen levels. This research focuses exclusively on postmenopausal overweight-to-obese women who are at an elevated risk of developing breast cancer. The results from these studies provide evidence that decreasing circulating estrogens can lower the risk of this group developing common types of breast cancer.

References:

Mason, C., Xiao, L., Imayama, I., Duggan, C., Wang, C., Korde, L., McTiernan, A. 2014. Vitamin D3 supplementation during weight loss: a double-blind randomized controlled trial. American Journal of Clinical Nutrition: 99(5): 1015-1025. doi: 10.3945/ajcn.113.073734

Campbell, K., Foster-Schubert, K., Alfano, C., Wang, C., Wang, C., Duggan, C., Mason, C., Imayana, I., Kong, A., Xiao, L., Bain, C., Blackburn, G., Stanczyk, F., McTiernan, A. 2012. Reduced-calorie dietary weight loss, exercise, and sex hormones in postmenopausal women: randomized controlled trial. Journal of Clinical Oncology.: 30(19): 2314-2326. doi: 10.1200/JCO.2011.37.9792

McTiernan, A., Tworoger, S., Ulrich, C., Yutaka, Y., Irwin, M., Rajan, K., Sorenson, B., Rudolph, R., Bowen, D., Stanczyk, F., Potter, J., Schwartz, R. 2004. Effect of exercise on serum estrogens in postmenopausal women: a 12-month randomized clinical trial. Cancer Research: 64: 2923-2928. doi: 10.1158/0008-5472.CAN-03-3393