There are two recent studies that I want to call attention to, that are relevant for our continued efforts to reduce the risk of breast cancer. The first addresses the issue of weight loss. In postmenopausal middle-aged women who lose weight and actually are successful in keeping it off, their risk of breast cancer is lower. Researchers studied over 180,000 women who were 50 y.o. or older and had their weight recorded 3 times over about 10 years. (wow— only 3 times!!!). The follow-up period for assessing invasive breast cancer started after the last weight measurement.
Over a period of 8 years, more than 6,900 invasive breast cancers occurred. After the researchers adjusted for baseline body mass index, the use of hormone therapy or not, and other select issues, women who had lost 2.0-4.5 kg and were successful in keeping the pounds off, had a 13% lower risk for breast cancer compared to women who had no weight loss and had stable weight. In those who kept off 9 kg or more, had even better results with a 26% reduction in risk (1 kg = 2.2 pounds). These benefits of weight loss and maintaining weight loss were strongest among overweight and obese women, meaning a body mass index of less than 25, and also among women with no history of using postmenopausal systemic hormone therapy.
Bottom line: If you are overweight and 50 or older, make every effort to lose weight a minimum of 4.5-10 lbs. and maintain that weight loss. Even better risk reduction if you achieve 20 lbs. weight loss and maintain that.
Reference: Teras L, et al. Sustained weight loss and risk of breast cancer in women ≥50 years: a pooled analysis of prospective data. JNCI: Journal of the National Cancer Institute, 2019. (early release online)
The second study is likely more controversial as is common with environmental exposures and disease risk and 
incidence. In an observational study of approximately 47,000 women in the U.S., questionnaires about their use of hair care products was used to assess breast cancer risk. These women were followed over 8 years. At entrance to the study, women did not have a history of breast cancer, but did have at least one sister who had a breast cancer diagnosis. Over the course of follow-up, 2,800 breast cancers were reported and after analysis, any use of permanent hair dye in the prior year was associated with a 9% increase in breast cancer risk, which is considered statistically significant. The risk was even greater for black women in the U.S., with an increased risk of 45%. Hair straighteners were less risky but did have an increased risk if they were used at least every 5-8 weeks.
We know from other research that the chemicals found in human hair dye, have been shown to cause mammary gland tumors in rats when those animals are exposed to those same chemicals. We also know that some hair straighteners contain formaldehyde, which is a known carcinogen.
These results on hair dye and hair straighteners are part of a larger study, called the Sister Study. The Sister Study is an ongoing study by scientists at the U.S. National Institute of Environmental Health Sciences (NIEHS) that includes 50,884 women living in the United States and Puerto Rico. The women joined the study between 2003 and 2009. The women were between the ages of 35 and 74 when they joined the study and none of the women had been diagnosed with breast cancer, but all had at least one sister who had been diagnosed. The Sister Study is looking at the causes of breast cancer and other health issues in women, as well as factors that influence quality of life and outcomes after a breast cancer diagnosis.
Bottom Line: Go au natural on the hair color and hair structure. Mother nature is a beautiful thing!!!
Reference: Eberle CE,et al. . Hair dye and chemical straightener use and breast cancer risk in a large U.S. population of black and white women. Int J Cancer; [Online 4 December 2019].
