Calcium is a macromineral required in gram amounts for good health. The typical Western diet is deficient in calcium, as it is of many minerals, and this has a number of physiological effects. The traditional view is that calcium is required for health bone formation, and this is true. However, calcium ions are important regulators of neuronal function, and intracellular calcium ions form part of elaborate second messenger systems that are pivotal to intracellular communication. Low calcium intake could therefore be predicted to upset the delicate calcium homeostasis of the body and cause dysfunctions in physiological systems unrelated to bone. One particular functions more recently attributed to calcium is in the maintenance of correct body weight. Low calcium intakes may increase the proliferation of adipocytes and decreased insulin sensitivity, thus driving weight gain and eventually leading to obesity. A large amount of data showing weight loss with calcium and dairy supplements supports this contention.
There is a great interest in foods that are protective of weight gain due to the large numbers of obese Westerners. Studies have investigated the associations between calcium intake and body weight. For example, in one study1, researchers evaluated correlations between calcium intake and body weight in 564 women. The results of the study showed that 16 % of women in the lowest 25 % intake for calcium (a level equivalent to 10 mg of calcium per gram of protein per day) were overweight, but only 4 % of the women who consumed the recommended intake of calcium (equivalent to 20 mg calcium per gram protein per day) were overweight. As calcium levels dropped the risk of being overweight therefore increased significantly. Women with calcium intakes in the lowest 25 % of intakes gained weight at midlife at a rate of 0.42 kg per year, whereas those women obtaining the recommended intake of calcium lost 0.011 kg per year. Low calcium diets are therefore associated with weight gain in middle aged women.
The authors of this study claimed that ensuring adequate and recommended calcium levels in all individuals would reduce levels of obesity by 60 to 80 %. This is a strong statement and one that is difficult to evidence as there are so many factors involved. However, the role of calcium in body weight changes is becoming more obvious as greater numbers of studies are published, and these studies all tend to show beneficial weight loss effects for calcium. Observational studies do not allow the cause and effect of the variables to be understood, and so in this observational study it is difficult to state that the calcium was the cause of the weight effects. The calcium intake could for example be a marker for a higher quality diet, which is then the cause of the weight loss. However, clinical trials do allow cause and effect to be deduced, and many clinical trials have shown weight loss effects from calcium and dairy supplements. Calcium may therefore be a contributory cause of the weight effects seen in this and other observational trials.
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