"Increasing total calcium intake, in the form of calcium supplementation, may be beneficial to weight maintenance, especially in women during midlife," wrote lead author Alejandro Gonzalez from the University of Washington, Seattle.
The controversy may arise from the different population groups that have been studied. A study from Purdue University claimed that young women could burn more calories if they ate three or four dairy servings per day. However another report, also from Purdue, reported that increased dairy consumption had no effect on weight gain or loss.
And a recent study from Denmark with young girls suggested that dairy intake did benefit weight loss but this effect was not solely due to calcium content, thought earlier to be responsible for the weight loss seen in some trials.
A new study, published in the Journal of the American Dietetic Association (Vol. 106, pp. 1066-1073), brings the focus of the debate back to calcium with the researchers concluding that calcium, in the form of supplements, could be beneficial for weight control, but only in women.
"This article presents the largest analysis of calcium use and weight change among free-living middle-aged men and women," said the researchers.
Retrospective data from 10,591 men and women aged between 53 and 57 were used to determine dietary calcium intake and weight change over an eight to 12 year period.
Data on dietary supplement use was evaluated by asking about the use of 38 vitamin, mineral, herbal, and other supplements during the ten years prior to the start. Diet was assessed using a 120-item food frequency questionnaire (FFQ), and demographic details were ascertained by another questionnaire.
The researchers found that the mean dietary calcium intake for women was 811 milligrams per day (mg/d) and 1,017 mg/d for men, while supplements added an average 283 mg/d for women and 98 mg/d for men. This shows that men were less likely to be calcium supplement users.
When weight gain was calculated with respect to calcium supplement intake, the researchers report: "Greater current daily dose of calcium supplementation was associated with significantly lower 10-year weight gain (5.1 kg) for [female] supplement dose of more than 500 mg compared to 6.9 kg for no supplemental calcium."
An even larger effect was observed when the female subjects were further divided into post-menopausal women receiving HRT or not. Non-HRT receiving non-supplement users had a 10-year weight gain of about 7.8 kg, while supplement users who did not receive HRT had an average 10-year weight gain of only 4.8 kg.
This could be explained, say the researchers, by an effect of calcium on female hormones, although reports from the literature on this are contradictory.
No significant associations were found between men and total dietary calcium intake (diet plus supplements).
There are several important limitations with this study; most notably that it is a based on the recall of volunteers. People who respond to such studies have been said to be more health conscious, have a higher education level, less likely to smoke, and more likely to take regular exercise.
The information about diet and supplement use was also self-reported, leading to potential recall errors for frequency and dosages. Also the diet evaluation was only performed once, which means the researchers made the assumption that diet for the entire 10-year period was relatively unchanged.
Bearing in mind these limitations, the researchers called for more evidence from randomized clinical trials to support the conclusion that calcium from diet and supplements does play a role in weight management.
"This study suggests that calcium supplements taken for other reasons (eg. prevention of osteoporosis) may have a small beneficial influence on reducing weight gain, particularly among women approaching midlife," concluded the researchers.
The report is in line with what Dr Michael Zemel from the University of Tennessee told attendees at the Paris Anti-Obesity Therapies congress at the end of May.
"The anti-obesity effect of dietary calcium is supported by cellular mechanistic studies, animal studies, human epidemiological studies and clinical trials," said Zemel.
However, Zemel also went on to say that that calcium only accounts for about 40 per cent of the effect that is observed with dairy in relation to weight loss.
Dairy industries in Europe and the US have been promoting milk-based products for consumers who want to slim for some time but the new findings underline that further work needs to be done to support their claims.
The EU recommended daily intake (RDI) of calcium is 800 mg, with an upper safe limit of 2500 mg.