Even a moderate amount of weight loss can considerably reduce levels of circulating estrogens, which are linked to an increased risk of breast cancer, according to a new study.
Research showed that overweight women who shed 5 per cent of their body weight are up to 50 per cent less likely to have the disease.
Anne McTiernan, M.D., Ph.D., and colleagues at Fred Hutchinson Cancer Research Centre conducted the first randomized, controlled clinical trial to test the effects of weight loss on sex hormones in overweight and obese postmenopausal women, a group at elevated risk for breast cancer.
"Based on previous research, our results suggest that losing just 5 percent or more of one`s weight could cut by a quarter to a half the risk for the most common, estrogen-sensitive breast cancers," said McTiernan, director of the Hutchinson Centre’s Prevention Centre and a member of its Public Health Sciences Division.
However, McTiernan insists that these findings only apply to overweight or obese women who are not taking hormone-replacement therapy.
Epidemiologists have long noted an association between obesity and increased risk of postmenopausal breast cancer.
A relationship between body fat and estrogen formation is thought to contribute to this risk.
The study was based on data from 439 overweight-to-obese, sedentary, Seattle-area women, aging between 50 to 75, who were randomly assigned to one of four groups.
These groups were, exercise only (mainly brisk walking), diet only, exercise plus diet and no intervention.
By the end of the study, participants on the diet-only and diet-plus-exercise regimen 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 estrogen (estrone, estradiol and free estradiol); two types of testosterone (total testosterone and free testosterone); a steroid necessary for the production of sex hormones (androstenedione) and sex hormone binding globulin, or SHBG, a protein that binds to sex hormones and therefore makes them biologically less active.
High levels of SHBG are associated with reduced breast cancer risk. Free estradiol and free testosterone are forms of the hormones that are not bound to SHBG and therefore are more biologically active.
At the end of the study, the researchers discovered 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.
The study found that Estrone levels decreased 9.6 percent with diet and 11.1 percent with diet plus exercise.
Estradiol levels reduced 16.2 percent with diet and 20.3 percent with diet plus exercise.
Besides this, 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.
While 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 advantageous impact on hormone levels, and the effect increased with the amount of weight lost.
"The amount of weight lost was key to changes in hormone levels," McTiernan said.
"The biggest effect was through diet plus exercise; exercise by itself didn`t produce much of a change in weight or estrogen,” she said.
She also revealed that exercise has many important profits for those on a weight-loss program. Exercise prevents loss of muscle and bone, and it helps keep off the weight long term.
"I recommend women both diet and exercise, because in the long run that should help keep weight down and therefore keep estrogens down," she said.
McTiernan claimed that 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 fiber significantly lowers blood estrogen levels in postemenopausal women.
"This shows that it`s never too late to make lifestyle changes to reduce your risk for breast cancer," she added.
The results of the research could also be relevant to overweight women, who take breast cancer prevention drugs such as tamoxifen, raloxifene and exemestane, which either block the action of estrogen or stop its production.
This study has been published in the American Society of Clinical Oncology.
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