MrOs is D-ficient.

Vitamin D deficiency is now being recognized as one of the most common medical conditions in the world (1). In the United States, the press coverage of the vitamin D deficiency epidemic and grassroots efforts to promote awareness about vitamin D for health have now made the 25-hydroxyvitamin D [25(OH)D] assay the most-ordered hormone assay in the United States. There continues to be debate as to what the optimal blood level of 25(OH)D is. Vitamin D deficiency is defined as a 25(OH)D level below 20 ng/ml (2), vitamin D insufficiency as 21–29 ng/ml, and vitamin D sufficiency as 30 ng/ml or above (3, 4). In this issue of JCEM, Orwoll et al. (5) report that 72% of men older than 65 yr throughout the United States were vitamin D insufficient. Vitamin D insufficiency was especially common in men living in northern communities and among the oldest and the most obese. The investigators used a state-of-the art, liquid chromatography tandem mass spectroscopy assay for measuring the serum 25(OH)D. This method not only gives an absolute quantitative level of total 25(OH)D but also provides the blood level of 25(OH)D3 and 25(OH)D2 individually (6). Throughout the world, there is a seasonal variation in the blood level of 25(OH)D that is reflective of exposure to sunlight (7). Sunlight provides most humans with their vitamin D requirement (1). Orwoll et al. (5) observed that men were at much higher risk of being vitamin D deficient in the winter compared with the fall. Outdoor activity, and therefore greater exposure to sunlight, was associated with a higher blood level of 25(OH)D. Aging decreases the capacity of the skin to produce vitamin D3 because the vitamin D precursor, 7-dehydrocholesterol, decreases with age. The capacity of human skin to produce vitamin D3 is large enough that even the 70% decline in the skin’s 7-dehydrocholesterol levels by age 70 yr (8) does not prevent older men and women from producing an adequate amount of vitamin D3 in their skin from casual sun exposure from outdoor activities (9). What was not mentioned by Orwoll et al. (5) was whether any sun protection was used during these outdoor activities. A sunscreen with a sun protection factor (SPF) of 30 absorbs approximately 99% of incident UV B radiation striking the skin that is responsible for making vitamin D3 (1). Thus, applying a sunscreen with an SPF of 30 reduces the ability of the skin to produce vitamin D3 by 99% (10). People of color have higher melanin content in their skin, which is an effective natural sunscreen. Thus, African-Americans and other people of color require longer exposure to sunlight to promote adequate vitamin D production in their skin (11). Therefore it was not unexpected that both African-Americans and Hispanics had lower blood levels of 25(OH)D compared with their Caucasian counterparts (5). Vitamin D deficiency is associated with obesity. Vitamin D is fat soluble and, thus, is incorporated into the body fat. For a normal-weight individual, this ability to store vitamin D in the body fat provides vitamin D to the body during the wintertime when sunlight is unable to produce vitamin D in the skin (1). However, for obese children and adults with a body mass index greater than 30 kg/m, the body fat sequesters the vitamin D, making it less bioavailable to the body. Wortsman et al. (12) reported that when obese adults were placed in a tanning bed and exposed to the same amount of UV B radiation as normal-weight healthy adults, they were only able to raise their blood level of vitamin D to about 45% compared with a normal-weight adult. A similar observation was made when they ingested 50,000 IU of vitamin D2 (12). Thus, obese children and adults require at least twice the amount of vitamin D as normal-weight individuals to sustain their blood levels of 25(OH)D above 30 ng/ml (1). For every 100 IU of vitamin D2 or vitamin D3 that is ingested, the blood level of 25(OH)D increases by 1 ng/ml (6, 13). Orwoll et al. (5) reported that men who took a supplement containing 400 IU of vitamin D had marginally higher blood levels of 25(OH)D when compared with those men who were not taking a supplement. On average, the men who ingested between 400 and 599 IU of vitamin D/d had 4.7 ng/ml higher blood levels of 25(OH)D compared with the group that was taking 0–199 of vitamin D/d from dietary sources. Thus, based on the observations of Orwoll et al. (5) and others, it is clear that to raise the blood level of 25(OH)D more than 30 ng/ml, at least 1000 IU of