Importance of Vitamin D

From the September 2005 edition of Dr. Fuhrman's Healthy Times:

Vitamin D is a fat-soluble vitamin that your body makes after exposure to ultraviolet (UV) rays from the sun. Vitamin D functions as a hormone because it sends a message to the intestines to increase the absorption of calcium and phosphorus. By promoting calcium absorption, vitamin D helps to form and maintain strong bones.

Vitamin D also works in concert with a number of other vitamins, minerals, and hormones to promote bone mineralization. Research also suggests that vitamin D is important to maintain a healthy immune system, regulate cell growth, and prevent cancer. Vitamin D has been shown to protect against the development of autoimmune disease such as inflammatory bowel disease, multiple sclerosis, and rheumatoid arthritis. It also has been shown to be helpful in decreasing disease severity for those suffering with autoimmune disease.1

Sun exposure is perhaps the most important source of vitamin D because exposure to sunlight provides most humans with their vitamin D requirement. The further you live from the equator, the longer you need to be exposed to the sun in order to generate vitamin D. Season, time of day, cloud cover, smog, and sunscreen affect UV ray exposure and vitamin D synthesis. For example, sunlight exposure from November through February in Boston is insufficient to produce significant vitamin D synthesis in the skin. Recent data have demonstrated that getting sunshine during the summer months is simply not enough; besides, most adults work indoors for the majority of the day, avoiding the sun. Sunscreens block UV rays that produce vitamin D, so they could contribute to our epidemic of vitamin D deficiency.

It is extremely important for individuals with limited sun exposure to ingest supplemental vitamin D. I still recommend that you routinely use sunscreen to help prevent skin cancer, wrinkling, and aging of the skin, especially because the ozone layer has been depleted. The risk of skin damage and skin cancer is real.

Americans age 50 and older are at increased risk of developing vitamin D deficiency. As people age, skin cannot synthesize vitamin D as efficiently, and the kidney is less able to convert vitamin D to its active hormone form. It is estimated that as many as 30-40 percent of older adults with hip fractures are vitamin D insufficient.2 Therefore, older adults especially benefit from supplemental vitamin D.

Melanin is the pigment that gives skin its color. The high melanin content in darker skin reduces the skin’s ability to produce vitamin D from sunlight. It is very important for African-Americans and other populations with dark-pigmented skin to consume recommended amounts of vitamin D. Some studies suggest that older adults in these groups, especially women, are at extremely high risk of vitamin D deficiency. It is thought that the main reason prostate cancer is so prevalent in black men is because of increased need for vitamin D.

For more on vitamin D, check out these previous posts:
1. Cantorna MT, Zhu Y, Froicu M, Wittke A. Vitamin D status, 1,25-dihydroxy-vitamin D3, and the immune system. Am J Clin Nutr 2004 Dec;80(6 Suppl):1717S-20S. Hein G, Oelzner P. Vitamin D metabolites in rheumatoid arthritis: findings—hypotheses-consequences. Z Rheumatol 2000;59 Suppl 1:28-32.

2. Holick MF. McCollum Award Lecture, 1994: Vitamin D: new horizons for the 21st century. Am J Clin Nutr 1994;60:619-30.
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Comments (2) Read through and enter the discussion with the form at the end
John Gilpin - March 9, 2007 10:42 AM

Although the season is about over now, one of the important functions of vitamin D is to help fend off flu.

An interesting discussion of this is at:

Edward Hutchinson - March 10, 2007 4:27 PM

Here are a couple more articles which add to this discussion and provide some interesting new research to support it.
Epidemic Influenza And Vitamin D
The Antibiotic Vitamin
Deficiency in vitamin D may predispose people to infection

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