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Obesity and Weight Management The Impact of Vitamin D on Weight Loss Rebecca L Thomson, PhD Research Fellow, Nutritional Physiology Research Centre, School of Health Sciences, Sansom Institute for Health Research, University of South Australia, Adelaide, Australia Abstract The incidence of vitamin D deficiency is increasing and 25-hydroxyvitamin D (25OHD) levels, which are inversely associated with measures of obesity, are lower in overweight and obese populations. There have been several studies that have investigated the effect of vitamin D supplementation on weight loss, and studies combining weight loss interventions with increased vitamin D intake, either through supplementation or foods fortified with vitamin D. 25OHD levels have also been measured before and after weight loss to see if they improve and if the changes in 25OHD levels are related to the degree of weight loss. Some studies have suggested that vitamin D status is associated with weight loss success, with supplementation resulting in weight loss, or higher baseline 25OHD or greater increases in 25OHD levels associated with greater weight loss, although this has not been shown in all studies. Keywords 250HD, weight loss, obesity, vitamin D deficiency, body composition, season Disclosure: The author has no conflicts of interest to declare. Received: August 28, 2013 Accepted: November 20, 2013 Citation: US Endocrinology 2013;9(2):146–52 Correspondence: Rebecca Thomson, PhD, Nutritional Physiology Research Centre, University of South Australia, GPO Box 2471, Adelaide 5001, Australia. E: rebecca.thomson@unisa.edu.au Along with the increased prevalence of obesity, the incidence of vitamin D deficiency is rising with 10–60  % of adults having values lower than 20  ng/ml. 1,2 Serum or plasma 25-hydroxyvitamin D (25OHD) is the most widely accepted measure of vitamin D status (deficiency <20  ng/ml, insufficiency 20–29 ng/ml, and sufficiency >30 ng/ml). Many studies have shown it is inversely associated with measures of obesity and that obese participants have lower suboptimal 25OHD levels compared with healthy weight participants. Adipose tissue sequesters the fat-soluble vitamin and this leads to lower levels in obese populations. It is also thought that obese people may spend less time outdoors, or expose less skin to the sun, which may lead to reduced synthesis of vitamin D. There has been increasing interest regarding the relationship between vitamin D, obesity, and weight loss, and this article will examine several aspects of this relationship, specifically looking at the effects of vitamin D supplementation and 25OHD levels on weight loss in adults. Possible mechanisms for the relationship between vitamin D and weight loss have been proposed. 3,4 Inadequate vitamin D status has been suggested to promote greater adiposity through the regulation of parathyroid hormone (PTH) and modulation of adipogenesis. Increased PTH, a consequence of low vitamin D levels, promotes calcium influx into adipocytes and this intracellular calcium enhances lipogenesis and inhibits catecholamine- induced lipolysis, leading to accumulation of fat and weight gain. 5,6 Achieving adequate vitamin D levels will lower PTH levels, which diminishes the calcium influx into adipocytes and increases lipolysis. 1,25-dihydroxyvitamin D, the active form of vitamin D, has also been shown to induce apoptosis in adipocytes. 7,8 It has also been suggested that lower PTH levels via an 146 increase in vitamin D levels could lead to weight loss through a sympathetic nervous system-mediated thermogenesis and lipolysis. 3 Does Vitamin D Supplementation Lead to Weight Loss? Several studies have investigated the effect of vitamin D supplementation on weight loss (see Table 1), although all were not specifically designed to analyze this. A secondary finding from a randomized controlled trial in men with impaired glucose tolerance designed to investigate glucose and lipid metabolism found a small but significantly greater weight reduction of 1.3 % using low-dose vitamin D compared with the placebo group with no weight loss after 3 months. 9 Interestingly, 25OHD levels significantly increased in both groups, but there was a greater increase in placebo, although not reported as significant (14 % versus 39 %); consequently, it is difficult to conclude if the greater weight reduction was due to the low dose supplementation despite greater increase in placebo, which suggests a possible seasonal impact. Following on from that study, the investigators conducted a longer uncontrolled study at a higher dose in 14 middle aged men with impaired glucose tolerance to investigate the effects on insulin sensitivity and glucose tolerance. Again, they found a small 1.1  % reduction in weight after supplementation for 18  months. 10 25OHD levels were only measured after treatment and 6 months later so the study was unable to report if the low-dose supplementation increased 25OHD levels. Six months after supplementation 25OHD levels increased 37  %, 10 suggesting a seasonal effect, which is likely since the study started and finished in the Fall. © TOU C H ME D ICA L ME D IA 2013