Dieting May Lower Hormone Levels Tied to Breast Cancer

New research suggests that weight loss through exercise and dieting helps overweight women lower the levels of certain hormones in their blood, potentially raising the odds that they'll avoid developing breast cancer.

The findings don't prove that losing weight this way will prevent breast cancer. Still, women who take medications to prevent the disease "need long-term solutions for managing their risk," study co-author Dr. Anne McTiernan, director of the Prevention Center at the Fred Hutchinson Cancer Research Center, said in a news release from the center.

"Weight loss represents an additional option for long-term breast cancer risk reduction without significant or bothersome side effects," McTiernan added.

The study is published in the May 21 online issue of the Journal of Clinical Oncology.

Previous research at the center has suggested 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," McTiernan said.

In the new study, researchers wanted to understand how weight loss through exercise, diet or both would affect potentially dangerous levels of hormones in the body.

The investigators randomly assigned 439 overweight-to-obese women to one of four groups. One group exercised (mainly through walking), one group dieted, one group did both and the remaining group did neither. The women were aged 50 to 75 with an average age of 58.

Those who dieted or dieted and exercised lost an average of about 10 percent of their weight. In addition, they lowered the levels of several hormones.

"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."

Dr. Robert Hiatt, professor and chair of the department of epidemiology and biostatistics at the University of California, San Francisco, cautioned that weight loss has been connected to breast cancer risk after menopause only. "In this stage of a woman's life, most of the circulating estrogens are no longer coming from the ovaries, which cease to function, but from fat tissue that is capable of producing the same types of estrogens," said Hiatt, who's familiar with the study findings.

He cautioned that "the study does not say that losing weight lowers the risk of breast cancer. It would take a larger and longer study to prove that. It does, however, suggest than weight loss has the right kind of effect on circulating estrogens, and it would be reasonable to expect that breast cancer rates would subsequently fall in such women."

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By By Randy Dotinga