A new study shows that even moderate weight loss could reduce the risk of breast cancer by lowering the levels of oestrogen in the body.
The new research, published in the Journal of Clinical Oncology, and conducted by the Fred Hutchinson Cancer Research Centre in the USA is the first randomised, controlled clinical trial to test the effects of weight loss on sex hormones in overweight and obese post-menopausal women.
Medical researchers have long noted a link between obesity and increased risk of breast cancer in postmenopausal women. A relationship between body fat and oestrogen production is thought to contribute to this risk.
Researcher, Dr Anne McTiernan, says they found that losing as little as five per cent of one’s total body weight had a beneficial impact on hormone levels, and the effect increased with the amount of weight lost.
Dr McTiernan says this is the first study to show that losing weight through a healthy diet that included reducing calories, reducing fat and increasing vegetables, fruits and fibre significantly lowers blood oestrogen levels in post-menopausal women.
“This shows that it’s never too late to make lifestyle changes to reduce your risk for breast cancer,” she says.
The study shows that the amount of weight lost is key to changes in hormone levels.
Dr McTiernan says: “The biggest effect was through diet plus exercise; exercise by itself didn’t produce much of a change in weight or oestrogen. I recommend women both diet and exercise, because in the long run that should help keep weight down and therefore keep oestrogens down.”
The study was based on data from 439 overweight-to-obese, sedentary, Seattle-area women, ages 50 to 75, who were randomly assigned to one of four groups: exercise only (mainly brisk walking), diet only, exercise plus diet and no intervention. At the end of the study, participants on the diet-only and diet-plus-exercise arms lost an average of 10 percent of their starting weight, which was the goal of the intervention.
The study measured the effects of diet- and exercise-related weight loss on blood levels of several types of sex hormones, including:
• three forms of oestrogen (estrone, estradiol and free estradiol)
• two types of testosterone (total testosterone and free testosterone)
• a steroid necessary for the production of sex hormones (androstenedione)
• sex hormone binding globulin, or SHBG, a protein that binds to sex hormones. (High levels of SHBG are associated with reduced breast cancer risk.)
At the end of the study, the researchers found significant reductions in hormone levels among the women who received the dietary weight loss intervention, with the most striking results among those who both dieted and exercised:
• Estrone levels decreased 9.6 percent with diet and 11.1 percent with diet plus exercise
• Estradiol levels decreased 16.2 percent with diet and 20.3 percent with diet plus exercise.
• Free-estradiol levels decreased 21.4 percent with diet and 26 percent with diet plus exercise.
• SHBG levels increased 22.4 percent with diet and 25.8 percent with diet plus exercise.
• Free-testosterone levels decreased 10 percent with diet and 15.6 percent with diet plus exercise.
The researchers found that losing as little as 5 percent of one’s total body weight had a beneficial impact on hormone levels, and the effect increased with the amount of weight lost.
Dr McTiernan cautions that these findings only apply to overweight or obese women who are not taking hormone-replacement therapy.
However, she says results of the study could be relevant to overweight women who take breast cancer prevention drugs such as tamoxifen, raloxifene and exemestane, which either block the action of oestrogen or stop its production.
“None of these medications are recommended for use beyond about five years, and they can have significant side effects in some women. Therefore, women need long-term solutions for managing their risk,” McTiernan said. “Weight loss represents an additional option for long-term breast cancer risk reduction without significant or bothersome side effects.”
The research was funded by the National Institutes of Health, the National Cancer Institute and the Canadian Institutes of Health funded the research. The study also included investigators at Harvard Medical School, the National Cancer Institute, the University of British Columbia, the University of Illinois and the University of Washington.
