Postmenopausal women who want to significantly decrease their breast-cancer risk would be wise to exercise regularly and keep their weight within a normal range for their height, according to new findings from the Women's Health Initiative recently published in the journal Obesity.
A multicenter team of researchers, led by Dr. Anne McTiernan of the Public Health Sciences Division, found that women who had the lowest body-mass index, or BMI, and the highest physical-activity levels had the lowest levels of circulating estrogens, sex hormones that can fuel breast-cancer growth. Specifically, they found a significant decrease in the two most common, biologically active forms of estrogen — estrone and estradiol — among the most active, lean women studied.
"Women with high levels of estrogens have a two- to four-times higher risk of breast cancer than women with very low levels," said McTiernan, a co-investigator of the Women's Health Initiative Clinical Coordinating Center, which is based at the Hutchinson Center. "If a woman can keep her own natural estrogens lower after menopause, it is probably going to be beneficial in terms of reducing her risk of breast cancer."
The study, based on a random sample of 267 postmenopausal women nationwide selected from the WHI Dietary Modification Trial, is the first of its kind to examine the dual impact of body weight and physical activity on levels of various circulating sex hormones thought to impact cancer risk.
"Other studies have looked at the impact of body weight by itself or physical activity by itself, but this is the first to look at both together regarding their influence on hormone levels," McTiernan said. "This gives us a new understanding that combining weight control with high levels of physical activity is necessary for keeping estrogens at a healthy level in postmenopausal women." Exercising vigorously for 30 to 60 minutes a day, five days a week would achieve this benefit, McTiernan said.
The researchers found that women with high BMI/low physical activity had a mean estrone concentration of 28.8 picograms per milliliter as compared to a concentration of 18.4 picograms per milliliter among women with low BMI and high activity levels. Similar trends were observed for estradiol levels.
BMI is a measure of body fat based on height and weight. The World Health Organization divides BMI into the following categories for both men and women: underweight (18.5 or lower), normal (18.5 to 24.9), overweight (25 to 29.9) and obese (30 or greater). A BMI calculator is available on the National Institutes of Health Web site at http://nhlbisupport.com/bmi/bmicalc.htm.
The National Heart, Lung and Blood Institute, U.S. Department of Health and Human Services, funded the study, which also involved investigators from Harbor-UCLA Research and Education Institute, Albert Einstein College of Medicine, University of Pittsburgh, University of Florida, University of Southern California and Northwestern University.
More than 500 Seattle-area participants are sought for the National Cancer Institute-funded Nutrition and Exercise for Women (NEW) Study. The study, led by Dr. Anne McTiernan, examines the effects of exercise and nutrition on breast-cancer risk factors.
The researchers seek healthy, overweight and sedentary postmenopausal women (ages 50 to 75) who live in the Seattle area and are willing to travel to the Hutchinson Center for the yearlong exercise or nutrition intervention.
Eligibility requirements include being a nonsmoker, not using hormone therapy for the past six months, getting less than an hour of moderate activity per week, and being above a certain weight threshold, depending upon height.
Those who qualify must be willing not to participate in any other exercise or weight-loss programs during the 12-month study enrollment and must be willing to be randomly assigned to one of the following four groups:
At the end of the yearlong study, these women will receive a free, two-month pass to the Center's state-of-the-art exercise facility and get to work out under the supervision of a personal trainer. They'll also get a chance to attend four group weight-loss meetings and will receive a variety of educational handouts about diet and exercise.
The study will be conducted at the Prevention Center, located in the Arnold Building. Designated parking for study participants is free of charge. For more information, call the NEW Study information line at (206) 667-6444, e-mail email@example.com or visit www.thenewstudy.org.