Scientists at The Institute of Cancer Research, London, found that in postmenopausal women, reductions in body mass index (BMI) were associated with lowered blood levels of hormones linked to breast cancer.
The research – funded by Breakthrough Breast Cancer and published in theJournal of Clinical Endocrinology & Metabolism – suggests that a woman’s risk of developing breast cancer after the menopause might be reduced by losing weight.
Higher levels of the sex hormone oestrogen have been linked to increased breast cancer incidence. Previous studies have shown that high BMI is associated with raised oestrogen levels, and have also suggested that obese postmenopausal women could see their risk of developing breast cancer decrease if they lose weight. But no study has previously shown that women of normal weight could reduce their hormone levels over time if they lost weight.
Here, researchers at The Institute of Cancer Research (ICR) took blood samples and BMI readings for 177 postmenopausal women from the Breakthrough Generations Study, a major investigation of over 100,000 women into the causes of breast cancer. Changes in BMI were measured and compared against levels of the sex hormones estradiol – an important form of oestrogen found in the body – and testosterone.
The researchers found that over a period of several years, changes in BMI were associated with significant changes in estradiol and testosterone levels. They found that decreases in BMI were linked to large decreases in estradiol, with every unit of BMI (kg/m2) a woman lost during the study resulting in a 12.7% decrease in the amount of estradiol measured in their blood. Lowering BMI was associated with similar decreases in testosterone, with each unit of BMI linked to a 10.7% fall.
The results suggest that weight loss for postmenopausal women could lead to substantial decreases in estradiol and testosterone levels, and support the idea that weight loss by these women could lessen breast cancer risk.
Dr Michael Jones, Statistician in the Aetiological Epidemiology Team at The Institute of Cancer Research, said: “There are studies that have correlated a woman’s BMI with levels of the hormone estradiol at that time, but they haven’t looked at BMI changes in postmenopausal women or changes in estradiol levels over time. This study clearly shows that a decrease in BMI is associated with reductions in estradiol levels for post-menopausal women, which in turn might reduce their risk of developing breast cancer. It adds extra support for maintaining a healthy weight, particularly for women approaching, and after, the menopause.”
Julia Wilson, Director of Research at Breakthrough Breast Cancer, said: “We know that a reduction in oestrogen in postmenopausal women can be a valuable protection against breast cancer, so this new research – correlating BMI with levels of estradiol – will strengthen existing advice that women, particularly post-menopause, should maintain a healthy weight to reduce their risk of breast cancer.
“The Breakthrough Generations Study is a vital source of information to help us better understand the causes of breast cancer and, as evidenced here, knowing what steps women can take to manage their own risk of developing the disease could prove to be one of the most important tools at our disposal.”