Study: Obesity, Estrogen Linked to Postmenopausal Breast Cancer

Postmenopausal women can significantly reduce their risk of breast cancer by maintaining a healthy weight, according to a new study by British researchers.

Reporting in the Journal of the National Cancer Institute, the Cancer Research UK scientists also added fuel to the theory that fat cells release the hormone estrogen into the blood, allowing it to help turn normal cells cancerous.

The researchers looked at eight separate studies around the world and compared Body Mass Index (BMI) and sex hormone levels in 624 breast cancer patients and 1,669 healthy women.

"Breast cancer risk increased with increasing BMI," the researchers reported. And the more the women weighed, the higher their levels of a form of estrogen called estradiol.

"The results are compatible with the hypothesis that the increase in breast cancer risk with increasing BMI among postmenopausal women is largely the result of the associated increase in estrogens, particularly bioavailable estradiol," the researchers reported.

The researchers found that breast cancer risk was 18 per cent higher for women with a BMI over 30 -- the threshold of obesity -- compared to those with a BMI of 25, regarded as the maximum of the healthy weight range.

"Women's risk is affected by many fixed factors – a family history of the disease, the number of children they have, the age they have their children, when they start their periods and when they stop," said lead researcher Dr. Tim Key of the Cancer Research UK Epidemiology Unit at Oxford University.

"But obesity is something that women have a level of control over," Key said. "Put simply, maintaining a healthy weight avoids extra breast cancer risk for these women."

Other Sources: Journal of the National Cancer Institute