The results of the current study are from a secondary analysis of a randomized activity and calcium supplementation trial in preschool children. Wide ranges in both mean dietary calcium (306–1799 mg/d) and percentage body fat (17–39%) were observed in our population, which provided sufficient variation to observe a relation. This analysis found no consistent relation between changes in total percentage body fat in young children and either dietary calcium intake or total calcium intake, even when the analyses were limited to the children in the lowest tertile of calcium intake or the lowest tertile of energy intake. We did find, among children in the lowest tertile of dietary calcium intake, a smaller gain in fat mass among children randomly assigned to receive calcium supplements than in children randomly assigned to receive placebo. However, the correlation between change in fat mass and total calcium intake, from both diet and supplements, was not significant in this group of children and did not support the hypothesis that changes in fat mass were associated with increased calcium intake.
In a population similar in age to ours, Carruth and Skinner (4
) found that total percentage body fat at 6 y of age was negatively associated with the number of servings per day of dairy products consumed between 2 and 5 y of age. We could not replicate these findings when we looked at changes in percentage body fat over the 1-y study. Although, theoretically, early calcium intake may affect body composition later in life, we are unaware of any other studies other than the one conducted by Carruth and Skinner that have reported this finding.
BMI decreases between the ages of 2 to 5 y, with a nadir at approximately 4 y, and then rebounds after the age of 5 y. We found that percentage body fat decreased significantly in this age range in both boys and girls, and perhaps the effect of high calcium intakes would be more apparent at ages when percentage body fat is increasing. The mean age of the subjects in the other published study (2
) in young children was significantly greater than in ours (6 y compared with 4 y of age).
It has been hypothesized that dietary calcium from dairy sources, and not calcium from nondietary sources, is associated with decreases in body fat (7
). Other components of dairy products, not analyzed in this study, could be the factor that influences body weight. Conjugated linoleic acid (CLA) has been suggested as one factor responsible for the effects of dairy products on body weight and adiposity. Mice fed CLA-supplemented diets have lower body weights (8
), lower amounts of body fat (9
), and higher amounts of lean mass (10
) than do controls. However, studies by Zemel et al (1
) indicate that nonfat dairy products, which do not contain CLA, also prevent increases in body fat in genetically obese mice; this finding suggests that the effect of dairy products on body fat changes are not due to CLA content. Although we did not specifically identify the amount of calcium that came from dairy sources, in this age group and at the time this study was conducted (1997–2001) a large percentage of dietary calcium was likely to have come from dairy products because foods consumed by this age group were not typically fortified with calcium. The finding of a significant difference in fat mass gain between the calcium and the placebo groups suggests that calcium was responsible for this effect rather than some other component of dairy foods.
High calcium intakes suppress 1,25-dihydroxyvitamin D concentrations, which has been reported to play a role in lipolysis and in the regulation of thermogenesis (7
). Studies in obesity-prone genetic mice have found that suppression of 1,25-dihydroxy-vitamin D with the feeding of high-calcium diets leads to increased thermogenesis (10
), and a recent study reported that higher calcium intakes are associated with higher rates of whole-body fat oxidation (11
). These findings indicate that the effect of increased calcium intakes on changes in total body fat is likely to be observed in persons who typically have low calcium intakes. Although we observed a difference in fat mass gain between calcium and placebo groups, we could not detect a relation between changes in total percentage body fat or fat mass and total calcium intake in children who were in the lowest tertile of dietary calcium intake.
Some individuals have proposed that the beneficial effect of calcium intake on body weight and fat mass is limited to those with low energy intakes. In their retrospective analysis of data from a 2-y prospective study of exercise among women aged 18–31 y, Lin et al (3
) found that calcium intake predicted a greater weight and fat mass loss only in those women who had lower energy intakes. We were not able to discern such a relation in young children in the current study. Although we observed a significant decrease in mean total percentage body fat in this age group, all children gained weight over the 1-y study.
In summary, we found that children in the lowest tertile of dietary calcium intake who were randomly assigned to receive supplemental calcium had lower gains in fat mass than did children randomly assigned to receive placebo. However, we did not observe a significant correlation between changes in fat mass and total calcium intake in these children, which suggests that if calcium intake is important, it is a weak relation that exists only among children with low dietary calcium intakes. If children consume the recommended dietary intakes of calcium to optimize bone health, additional calcium is not likely to prevent fat mass accumulation.