Study: Higher Body Mass Index Associated with Lower Breast Cancer Risk in Younger Women

Higher body mass index (BMI) may be associated with a lower risk of breast cancer in premenopausal women, even for women within a normal weight range, according to new findings.

A study published in JAMA Oncology focused on the drivers of breast cancer risk in younger women before menopause. Although obesity has been linked to higher breast cancer risk in women after menopause, this risk factor may be reversed in younger women who have not reached menopause age, according to the study authors.

The researchers pooled data from 19 different studies to investigate breast cancer risk for a group of 759,592 women who were younger than 55 years. The analysis demonstrated a trend in which higher BMI was associated with lower breast cancer risk.

According to the findings, the largest risk reductions were for BMI between the ages 18 and 24, with a 23% lower breast cancer risk linked to each 5-unit increase in BMI during this time period. Each 5-unit increase in BMI was linked to a 15% lower risk at ages 25 to 34, 12% lower risk at ages 35 to 44, and a 12% lower risk at ages 45 to 54 years old.

Additionally, the findings indicated risk decreases linked to higher BMI for estrogen- or progesterone-receptor positive breast cancer but did not demonstrate a consistent relationship for BMI and triple-negative breast cancer or hormone-receptor negative breast cancer.

The researchers noted potential factors contributing to the link between BMI and breast cancer risk, such as differences in hormones, including estrogen, growth factors, or breast density.

“Although breast cancer is more common at older ages, it’s actually the most common type of cancer diagnosed among reproductive-aged women,” study author Hazel B Nichols, PhD, assistant professor in the UNC Gillings School of Global Public Health, said in a press release. “Understanding the risk factors that may operate differently before menopause is critical to reducing breast cancer risk in young women, but these factors are hard to study in traditional settings where there are few young women in cancer research.”

Dr Nichols noted that the research team will conduct further investigation into patterns of risk according to weight change in early-to-mid adulthood, as well as the role of pregnancy and other factors that may contribute to breast cancer risk at younger ages. Understanding the biological mechanisms underlying these associations could have important preventive potential, the researchers concluded.

Reference

The Premenopausal Breast Cancer Collaborative Group. Association of body mass index and age with subsequent breast cancer risk in premenopausal women. JAMA Oncology. 2018. doi: 10.1001/jamaoncol.2018.1771

Higher body fat linked to lower breast cancer risk in younger women [news release]. UNC’s website. https://unclineberger.org/news/body-fat-lower-breast-cancer-risk. Accessed June 21, 2018.