Vitamin D: Important for Prevention of Osteoporosis, Cardiovascular Heart Disease, Type 1 Diabetes, Autoimmune Diseases, and Some Cancers

Michael F. Holick, MD, PHD


South Med J. 2005;98(10):1024-1027. 

In This Article


Vitamin D deficiency is common in all age groups. Even young children and young and middle-aged adults are at significantly increased risk of vitamin D deficiency.[28,31,32,33,34,35,36] This is in part due to the fact that there is very little vitamin D in the diet, and increased use of sunscreens and diminished outdoor activity also contribute to this problem. More than 90% of the human vitamin D requirement comes from casual exposure to sunlight.[1] Wearing a sunscreen with an SPF of 8 reduces the ability of the skin to produce vitamin D by 95%.[37] Thus, judicious exposure to sunlight typically no more than 5 to 15 minutes per day (depending on latitude, time of day and degree of skin pigmentation) of arms and legs or hands, face, and arms two to three times per week during the spring, summer, and fall in latitudes above 37º and throughout the year below 37º is all that is required to satisfy the body's requirement.[38] A yearly measurement of 25(OH)D during the annual physical examination is prudent not only to maximize bone health but also to prevent many chronic diseases that are linked with vitamin D deficiency (Fig. 3).

Photoproduction and sources of vitamin D. Vitamin D is metabolized in the liver to 25-hydroxyvitamin D [25(OH)D], which is responsible for maintaining calcium homeostasis. 25(OH)D is also converted to 1,25(OH)2 D in a variety of other cells and tissues for the purpose of regulating cell growth, immune function, as well as a variety of other physiologic processes that are important for the prevention of many chronic diseases (copyright Michael F. Holick, 2004, used with permission).


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