Postmenopausal women taking calcium and vitamin D supplements weigh about 0.13 kilograms less than counterparts not taking the supplements, results from the Women's Health Initiative have reported.
Moreover, the effect was even greater amongst women who were not consuming the recommended daily amount of calcium when the study started.
"To our knowledge, this is the largest double-blind, placebo-controlled, clinical trial to report the effects of calcium plus cholocalciferol (vitamin D) supplementation on weight change," wrote the authors in the Archives of Internal Medicine.
The study adds to the on-going debate of the role of calcium and vitamin D, mainly from dairy products, in weight loss. The topic is a source of controversy with both camps able to quote research that supports their side and undermines the other.
"Because weight loss or prevention of weight gain is likely to have significant health benefits for middle-aged women, early to middle menopause may be a critical period of life in which to slow the trajectory of weight gain," wrote lead author Bette Caan from Kaiser Permanente Northern California.
Over 300m adults are obese worldwide, according to latest statistics from the WHO and the International Obesity Task Force. About one-quarter of the US adult population is said to be obese, with rates in Western Europe on the rise, although not yet at similar levels.
The researchers recruited 36,282 postmenopausal women (average age 62.4 at the start), and randomly assigned them daily supplements containing 1,000 milligrams of calcium as calcium carbonate, plus 400 international units of vitamin D (18,176 women) or placebo (18,106 women). The women were followed for an average of seven years and weighed once a year, with 66 per cent of participants taking at least 50 per cent of the supplements over this time.
They report that, at the start of the study, 40 per cent of the women met current recommended daily intake of 1,200 milligrams of calcium, 54 per cent reported taking calcium supplements and 29 per cent reported taking supplements of 500 milligrams of calcium or more. After seven years of follow-up, women who took the supplements weighed an average of 0.13 kg (0.28 lbs) less than those who did not.
When the researchers looked at a subgroup of women not consuming the recommended amount of calcium daily before the study, the effect of supplementation with calcium plus vitamin D was greater, with women weighing an average of 0.2 kg (0.42 lbs) less than women in the placebo group.
This equated to an 11 per cent lower risk of weight gain during the three years of the trial, compared with calcium-deficient women in the control group, said the researchers.
They added that, while the women in the intervention group benefited from the supplements, the effect was only small in magnitude.
"The relatively small effect observed in the WHI may have been because the source of calcium supplementation was from non-dairy products," wrote Caan. "This finding is supported by several studies that showed larger beneficial effects from calcium derived from consumption of dairy products compared with supplements."
This would agree with statements by Dr. Michael Zemel from the University of Tennessee. At the Paris Anti-Obesity Therapies 2006 conference he said that dairy can help reduce body fat and that calcium only accounts for about 40 per cent of the effect.
"Further research should be undertaken to address the effect of calcium supplementation combined with caloric restriction and physical activity on weight gain prevention," they concluded.
Calcium and vitamin D are key performers in the dietary supplements industry, with calcium reported to be the biggest seller in the US supplements industry. Annual sales amounted to about $993m (€836m) in 2004, according to the Nutrition Business Journal.
Source: Archives of Internal Medicine
2007, Volume 167, Pages 893-902
"Calcium Plus Vitamin D Supplementation and the Risk of Postmenopausal Weight Gain"
Authors: B. Caan, M. Neuhouser, A. Aragaki, C.B. Lewis, R. Jackson, M.S. LeBoff, K.L. Margolis, L. Powell, G. Uwaifo, E. Whitlock, J. Wylie-Rosett; A. LaCroix