Contrary to what some studies have suggested, taking calcium supplements may not help overweight adults avoid further weight gain, U.S. researchers reported Monday.

The study, published in the Annals of Internal Medicine, found that calcium capsules had no effect on overweight and obese adults' weight over two years.

Earlier studies had found connections between calcium intake and weight. Both children and adults with low calcium intakes have been shown to have more body fat, on average, while other studies have linked low-calcium diets to greater weight gain over time.

The current study is the first large clinical trial to specifically test whether calcium supplements help prevent further weight gain in overweight adults — and the results suggest that they do not, report Dr. Jack A. Yanovski and colleagues at the U.S. National Institutes of Health (NIH).

The study, which was funded by the NIH, involved 340 overweight or obese adults with an average age of 39. Half were randomly assigned to take 1,500 milligrams of calcium carbonate every day with meals for two years. The rest were given placebo capsules for comparison.

At the outset, most participants were getting less than the recommended 1,200 milligrams of calcium per day.

After two years, the researchers found, there were no significant differences between the calcium and placebo groups in average weight, fat mass or waist size — all of which increased slightly in both groups.

In theory, calcium could help control weight for several reasons. For one, it combines with fatty acids in the intestines to form insoluble "soaps" that the body cannot absorb. In addition, low calcium levels in the body may cause more triglycerides (a blood fat) to be stored in fat cells.

Still, in reality, the current findings suggest that taking calcium has "limited efficacy" in preventing weight gain, Yanovski and his colleagues write.

They add, however, that some researchers believe there is something about dairy foods — not just calcium — that may affect metabolism and weight. "A limitation of our study," the researchers write, "is that we did not include participants randomly assigned to a high dairy calcium diet."