Obesity is increasingly being seen as a condition of systemic inflammation and oxidative stress. The accumulation of fat stimulates NAPDH oxidase in white adipocytes, resulting in the production of reactive oxygen species (ROS). This local oxidative stress in obesity causes a dysfunctional production of adipose cytokines (adipokines). Calcium has been shown to suppress fat gain during a eucaloric diet, and to accelerate fat loss during a hypocaloric diet, an anti-obesity effect might be due to calcium’s inhibition of circulating levels of 1,25-dihydroxycholecalciferol [1,25(OH2)D; calcitriol] (here). The physiological effects of 1,25-(OH2)D (via activation of the nuclear vitamin D receptor) increase fatty acid synthesis, inhibit lipolysis via modulation of Ca2+ influx, suppress uncoupling protein‑2 expression, and regulate ROS production, causing a decrease in adipocyte apoptosis. The promotion of glucocorticoid production by 1,25(OH2)D may also promote visceral fat accumulation.
Researchers1 have investigated the effects of calcium in a mouse model of obesity by feeding low calcium diets (0.4% as calcium carbonate), high calcium diets (1.2% as calcium carbonate) or a high calcium dairy diet (1.2% as calcium from milk). In this study, the researchers reported that the high calcium diet was able to lower oxidation (as measured by ROS generation, NADPH oxidase mRNA and plasma malondialdehyde) when compared to the low calcium diet. This effect was further enhanced by the high calcium dairy diet. Both of the high calcium diets also resulted in the suppression of tumour necrosis factor-α (TNFα) and interleukin-6 (IL6) mRNA, and expression of adiponectin and IL15 mRNA. The same researchers then used archived samples from clinical trials to assess the effects of diary on obese subjects and reported an 11% and 29% decrease in C-reactive protein on eucaloric and hypocaloric high-dairy diets.
These results support previous findings that show that high dairy diets may be protective of obesity, and also suggest that calcium may be able to regulate oxidative and inflammatory stress, with an additional effects coming from dairy when compared to calcium. As with many studies, the results here are compromised because of the sugars present in the different treatments. The low calcium non-dairy diet contained 33% more sucrose than the dairy diet to compensate for the presence of lactose, and it is possible that the low sucrose content contributed to the greater reduction in ROS. However, the high calcium (no dairy) control was evidence that calcium did have an effect on oxidative and inflammatory stress. The suppression of circulating 1,25(OH2)D on both the high calcium and high calcium dairy diets (with identical calcium contents) supports the hypothesis that some of the anti-obesity effects of calcium may be due to inhibition of 1,25-(OH2)D.
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