The current adult recommended intake of vitamin D is based on data collected from a decades old medical report on a handful of children with rickets, which is not relevant to healthy adults. In fact, recent evidence suggests that the optimal plasma concentration of the vitamin D marker 25-hydroxyvitamin D is much higher than was previously considered. A number of factors can influence the requirement for vitamin D, most notably the amount of sun exposure to the skin. In addition though, evidence suggests that obese and over weight individuals have in increased requirement for fat soluble vitamins such as vitamin D. This requirement arises because adipose tissue is able to sequester the vitamins from circulation, preventing them from performing their physiological functions. Therefore those overweight individuals with greater levels of adiposity may require higher intakes of certain fat soluble vitamins in order to prevent vitamin deficiencies.
If physical size and adiposity affect vitamin D requirements in adults, individuals with greater quantities of adipose tissue should experience smaller improvements to vitamin D status with supplemental vitamin D. This is exactly what the literature shows. For example, one study1 investigated the association between vitamin D intake and body size in 257 healthy men and women aged 65 years or over. Subjects were randomly assigned to receive either a supplement of 175µg/d (700IU/d) of vitamin D3 with 500mg/day of calcium, or a placebo. Following adjustments for sex, season and baseline vitamin D status (plasma 25-hydroxyvitamin D concentration), changes to vitamin D status were inversely associated with body mass index. Baseline vitamin D status was also inversely associated with the subject weight, waist circumference and body fat. Obese and overweight individuals may therefore have a higher requirement for vitamin D than lean counterparts.
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