Epidemiological research shows an inverse association between body weight and calcium intake. From this research the cause and effect of the relationship cannot be attributed. However, animal studies and clinical trials have shown that administration of higher intakes of dairy or calcium cause weight loss in overweight and obese animals and humans, respectively. The mechanisms of action by which calcium can cause weight loss may be related to the calcium paradox. This paradox describes the observation that when calcium intakes are low, cellular levels of calcium rise due to the stimulating effect of 1,25-dihydroxyvitamin D. High calcium levels interfere with insulin signalling and cause insulin resistance with concomitant weight gain. Increasing dietary calcium intake, lowers levels of 1,25-dihydroxyvitamin D and this causes intracellular calcium levels to fall, improving insulin sensitivity and allowing weight loss.
Because of the mounting evidence that calcium might play a role in weight maintenance through the actions of vitamin D metabolites, researchers1 have investigated the effects of calcium and vitamin D supplements on weight loss in a double-blind placebo controlled study. Subjects were fed three 240mL normal or reduced calorie orange drinks either fortified with calcium (1050mg) and vitamin D (300IU), or not fortified. After 16 weeks there was no significant difference in weight loss between the subjects in any groups. However in the calcium and vitamin D fortified orange juice group, visceral adipose tissue as measured by computed tomography scans was significantly reduced (-12/7cm2), compared to the orange juice control group. The calcium and vitamin D fortified calorie free orange juice caused even greater visceral adipose tissue loss (13.1cm2) when compared to the calorie free orange juice control group.
These results suggest that calcium combined with vitamin D causes weight loss in overweight individuals (body mass index between 25 and 35kg/m2). However, whether the effects were solely down to the consumption of calcium is not clear, as no suitable control was included in the study. Calcium and vitamin D may therefore play a role in maintaining insulin sensitivity, and supplementation of overweight individuals may specifically reduce abdominal adipose tissue thorough a reduction in insulin resistance. Overweight and obese individuals may have deficiencies in either or both calcium and vitamin D and as such be suffering from micronutrient deficiencies. Such deficiencies could be considered therefore to be a contributory factor in weight gain via abnormal metabolic function. This provides more evidence that the traditional view of weight gain being due to lethargy and greed is false and outdated.
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