Small weight loss effectively reduces sex hormones linked with breast cancer

Many studies have shown a link between obesity and an increased risk of contracting various forms of cancer.  So just how effective is weight loss in keeping cancer at bay?

A new study out of the Hutchinson Cancer Researcher Center has revealed even a small amount of weight loss effectively reduces the amount of circulating estrogens in the body– which are hormones that have been found to increase the risk of breast cancer in women.  Published in the Journal of Clinical Oncology, the study is the first clinical trial to examine the link between weight loss and the reduction of sex hormones in overweight and obese postmenopausal women, a major group at risk for breast cancer.

According to the study’s lead author, Dr. Anne McTiernan, the director of the Hutchinson Center’s Prevention Center, the study was inspired by previous research on the effects of exercise on sex hormones.

“In a previous study we'd shown that exercise alone can reduce estrogens and testosterone in postmenopausal women, but the effect was limited to women who lost weight,” McTiernan told  “So with this study, we wanted to see if the larger amount of weight loss you can get with reducing calories would have a bigger effect. And sure enough, it had a very large and significant effect.”

McTiernan and her colleagues collected data from 439 overweight-to-obese women aged 50 to 75 in the Seattle, Wash., area.  Each woman was randomly assigned to one of four categories – exercise only, diet only, exercise plus diet and no intervention.

Throughout the course of the study, the researchers measured blood levels of different types of sex hormones, including two forms of testosterone, three forms of estrogen, a steroid needed to produce sex hormones, and SHBG – a protein that binds to sex hormones rendering them less effective.

By the study’s conclusion, women in both the diet-only and diet-and-exercise group lost about 10 percent of their original weight, on average.  But even smaller amounts of weight loss were shown to drastically reduce sex hormones linked with breast cancer.

“We did find that the more weight someone lost, the more her estrogens and testosterone went down,” McTiernan said.  “However, just losing 5 percent of starting weight – such as losing 10 pounds if she started at 200 – had a significant effect. That's really promising news, I believe, because it's telling us that women don't have to be a ‘Biggest Loser’ to get an important health benefit.”

McTiernan said that after women go through menopause, while their ovaries may stop producing estrogen, other tissues – mostly fat tissues – continuing making the hormone.  The higher amounts of estrogen, the greater the risk for developing breast cancer.

“Fat cells have an enzyme called aromatase, which converts androgens into estrogens,” McTiernan said. “So women with high amounts of body fat tend to have high levels of estrogens. We think what happened for these women is that as they lost weight, their fat cells decreased in size and/or number, reducing the amount of aromatase available. So they couldn't produce as much estrogen.”

The study’s authors hope that their findings will encourage women to lead an active and healthy lifestyle.

Also, women shouldn’t feel intimidated about losing a substantial amount of weight, McTiernan added.

“You don't have to lose a huge amount of weight to have a significant health benefit from making lifestyle changes to reduce calories and increase physical activity,” McTiernan said. “These results are very relevant. Two-thirds of American women are overweight or obese, and that's increasing their risk of getting breast cancer.”