On the basis of preliminary evidence suggesting that increasing calcium intake might lead to reduced weight gain, we tested the hypothesis that dietary calcium could alter the amount of weight and body fat gained in overweight and obese patients. Two years of calcium supplementation, taken as capsules at meals, did not greatly alter either body weight or body fat gain in overweight and obese adults. Overweight and obese adults were selected as subjects because, when heavier individuals are followed longitudinally, they tend to show greater weight gain over time than normal weight adults (59
) and are at greater risk for the development of complications from excessive body weight gain (68
Previously published large trials of calcium supplementation were not designed with body weight as the primary endpoint; however, most have reported that additional calcium had insignificant effects on body weight (26
). Reid et al (26
) reported no difference in body weight or fat mass among 1471 women randomized for the purpose of fracture prevention to take 1g elemental calcium as calcium citrate or placebo for 30 months. However, a tertiary analysis of the 36,282 women who took part in the Women’s Health Initiative (WHI) trial (22
) found supplementation with 1000mg calcium plus 400IU cholecalciferol was associated with a small difference in body weight in the cohort (0.13kg) and lower risks for significant weight gain (1–3kg or >3kg) among those with dietary calcium intake <1200mg/d. The data for an effect of dairy or supplemental calcium on body weight from smaller clinical trials, many of which have also involved weight reduction programs, have been mixed (73
), with a few finding a significant impact (18
) and others (30
) failing to show any differences. Similar heterogeneity in results has been found when the impact of supplemental calcium on blood pressure is examined (79
). The current study is the first large randomized investigation specifically designed to examine if supplemental calcium could prevent weight gain. Given the relatively small impact of calcium on body weight found in the WHI and most other trials, we believe all of the data are consistent in suggesting limited efficacy for weight gain prevention among overweight or obese persons. The WHI result finding lower odds for gaining weight among those with low calcium intake who were given calcium and vitamin D supplements (22
) was not replicated in the present study. One limitation that may explain why we did not reproduce the WHI findings is that this study was not powered to detect very small differences in body weight that could be attributable to calcium. However, it would seem to be of little clinical importance to determine if a supplement could change average body weight by a fraction of a pound over several years, as suggested by the WHI trial. Indeed, a difference attributable to calcium of −0.13kg is well within the confidence interval for weight change in the present trial. Another possibility why the WHI regimen, which included vitamin D supplementation as well as calcium provision, was associated with weight change is that adequate vitamin D is required for calcium to be well absorbed. However, we found no impact of baseline 25-hydroxy-vitamin D concentrations on weight change in this study. Significant changes in dietary or supplemental calcium and vitamin D intakes could therefore also conceivably affect study results. Total intakes were formally assessed by validated questionnaires once yearly, and changes in supplemental intakes were assessed every three months in the present study, but we cannot rule out changes in intakes not detected by these methods. A final possibility is that, since the WHI findings were tertiary re-analyses and not the primary or even secondary purposes of the study, the WHI’s positive results may have occurred by chance.
Some investigators have suggested that dairy products, rather than calcium alone, may have greater effects on body weight (35
), and lipid metabolism (80
), a limitation of the present study is that it did not include subjects randomized to a high dairy calcium diet. It is also possible that some subjects’ dietary calcium intake was insufficiently low to demonstrate the impact of calcium supplementation. However, 75% of subjects consumed less than the daily recommended calcium intake, and one-quarter reported calcium intake <600mg/d; analyses restricted to either of these groups failed to show trends consistent with an impact of calcium on body weight gain. Another limitation is that adherence was measured only through counts of returned capsules and was not confirmed by other measurements. However, parathyroid hormone concentrations did decrease in the calcium-treated group, suggesting impact of the supplements. Finally, although this study’s participant demographic characteristics were similar to those reported for overweight individuals in the US, subjects were not recruited in a truly population-based fashion. Subjects who participate in research projects involving randomization may possibly be more health-conscious than the general population. Another sample-related limitation is that the groups studied consisted mostly of women. However, mean weight change in those who completed the study (+1.6kg over 2y) was quite similar to that reported in prior epidemiologic studies of adults measured longitudinally (81
In summary, supplementation with 1500mg per day of elemental calcium did not significantly alter weight or fat gain over a 2-year interval in overweight and obese adults. Thus, even though there may be other important reasons, such as fracture prevention (83
), to recommend dietary calcium supplementation, we conclude that the extant data suggest that calcium supplementation is unlikely to have clinically significant efficacy as a weight gain preventive measure in people who are already overweight or obese.