Vitamin D Status, Adiposity, and Exercise Performance

Abstract

INTRODUCTION Irealize that I wrote a column about vitamin D last year; however, I write on the topic now not because I had nothing else to write about for this Nutritionist’s View column, I simply want to keep with the theme of the current issue addressing obesity and weight loss and then include more data on vitamin D and exercise performance. I will not repeat what I wrote last year; however, I will give a similar background, both for new readers and those of you who may not have read my last column on vitamin D. Vitamin D is a required vitamin for humans and also is considered a hormone. That is because it is produced in one part of the body but works in another part of the body. The most active form of vitamin D is produced in the kidneys and is called ‘‘calcitrol’’ or ‘‘1,25-dihydroxyvitamin D3’’. The precursor to calcitriol is synthesized in the liver (25-hydroxyvitamin D or calcidiol), which is the onemeasured in the blood to assess if someone has a vitaminD deficiency or not because it stays in the blood longer than other forms of vitamin D and, therefore, can be better measured. The Dietary Reference Intake for vitamin D is 600 IU for individuals aged 1 through 70 years (5). Vitamin D can be obtained from food (e.g., salmon, sardines, fortified cow’s milk, soy milk, or orange juice) or through the sun on the skin (7). Vitamin D is well known for its role in bone formation; however, there is evidence that vitamin D plays a role in adaptive immune processes and may improve skeletal muscle function (8). Although it has been well established that vitamin D deficiency exists in obese individuals who are not athletes, little data exist on the vitamin D status of overweight or obese athletes. The reason for vitamin D deficiency in obesity likely is caused by vitamin D being stored in fat tissues (6).