WEDNESDAY, May 16 (HealthDay News) -- Postmenopausal women who take supplements with calcium and vitamin D gain slightly less weight than women not taking the supplements, researchers report.

While the effect on weight was small, it's another reason women should be taking calcium and vitamin D, which can help prevent osteoporosis, the study authors said.

"There was a small effect in the prevention of weight gain, approximately 5 percent," said lead researcher Bette Caan, a senior research scientist at Kaiser Permanente Northern California, in Oakland. "The effect was greatest at three years among women who had been taking less than the daily recommend amount [of calcium] before the trial. They were also more likely to stay stable or lose weight," she said.

For the study, Caan's team collected data on 36,282 postmenopausal women, ages 50 to 79. The women were part of the Women's Health Initiative clinical trial. In the trial, 18,176 women were randomly selected to receive a daily dose of 1,000 milligrams of calcium plus 400 international units of vitamin D, while 18,106 women were given a placebo once a day. Then, their weight was checked each year for seven years.

By the end of the trial, the researchers found that women who took the supplements weighed an average of 0.28 pounds less than those who did not.

Women who received the supplements and were getting less than the recommended amount of calcium daily before the start of the study weighed an average of 0.42 pounds less than those who did not. In addition, these women had a lower risk of putting on weight in both small amounts (2.2 pounds to 6.6 pounds) and moderate amounts (more than 6.6 pounds). And they were more likely to maintain a stable weight (within 2.2 pounds of their starting weight) or losing weight (more than 2.2 pounds), the researchers said.

Caan does not recommend taking calcium and vitamin D for the purpose of slowing weight gain. "However, since 1,200 milligrams of calcium is already recommended for postmenopausal women for bone health, they should continue with that recommendation, and it may be an extra benefit if it also helps reduce the risk of weight gain," she said. "They should not rely on calcium to prevent weight gain. It's not a magic bullet."

The study was published in the May 14 issue of the Archives of Internal Medicine.

One expert thinks calcium's small effect on weight gain is not really an effective part of fighting obesity.

"The beneficial effects on weight gain peaked after just three years, and then plateaued," said Dr. David Katz, director of the Yale University School of Medicine Prevention Research Center. The benefits of supplementation were reduced weight gain, not weight loss. Roughly 70 percent of the women in this trial were overweight at the start, and almost all gained weight throughout, he said.

"Calcium and vitamin D did not cause weight loss, or even prevent weight gain -- they just slowed its relentless march a bit," he said. "In the battle to control obesity and its adverse effects, this has contributed the equivalent of a pea shooter."

More information

For more information on maintaining a healthy weight, visit the U.S. Center for Food Safety and Applied Nutrition.

SOURCES: Bette Caan, Dr.P.H., Kaiser Permanente Northern California, Oakland; David Katz, M.D., M.P.H., director, Prevention Research Center, Yale University School of Medicine, New Haven, Conn.; May 14, 2007, Archives of Internal Medicine

Copyright © 2007 ScoutNews, LLC. All rights reserved.