SAN FRANCISCO — The burning issue of how best to make sure that patients get enough vitamin D comes down to this conclusion: Recommending intentional exposure to the sun is inappropriate, Dr. Henry W. Lim said.
For patients at risk of vitamin D deficiency, it is better to recommend a vitamin D-fortified diet and daily supplements of 800 IU of vitamin D (ideally vitamin D3) plus calcium, he said at the annual meeting of the American Academy of Dermatology.
Dr. Lim, chairman of the dermatology residency program at Henry Ford Hospital, Detroit, organized a 2005 consensus conference for the academy called Sunlight, Tanning Booths, and Vitamin D. At the annual meeting he discussed more recent data on vitamin D and presented his preferred approach to vitamin D management.
Intentional sun exposure is a problem because the harmful side effects of UVB can't be separated from the beneficial vitamin D photosynthesis that sunlight provides. UV light acutely damages skin DNA and can cause erythema, sunburn, and photoimmunosuppression. In the long term, UV irradiation leads to photoaging and possible photocarcinogenesis. Half of all cancers in humans are skin cancers.
In addition, vitamin D synthesis appears to occur at different rates in people of different skin types. That, plus significant daily and seasonal variability in weather patterns and availability of sunlight make it difficult to craft public health policies based on intentional sun exposure, Dr. Lim said.
Studies have identified certain populations that may not be getting adequate vitamin D, including the elderly, people with darkly pigmented skin, and those living in wintry climates. Other studies, however, show that most people achieve adequate vitamin D serum levels in the course of normal daily life, even when using sunscreen, presumably through incidental sun exposure, dietary intake, and supplementation, he added.
Recent data suggest that levels in U.S. whites averaged 80 nmol/L, “which is considered nowadays by most studies to be an adequate level of serum vitamin D,” Dr. Lim noted. In Hispanic Americans, however, serum levels averaged 60 nmol/L, and in U.S. blacks, serum vitamin D averaged 50 nmol/L.
Very modest sun exposure produces maximal vitamin D photosynthesis in fair-skinned people. This makes prolonged sun exposure unnecessary and potentially dangerous for these people, he said.
Separate data on individuals older than 60 years—who presumably are less active and spend more time indoors—suggest that 67% of whites and 88% of blacks have serum vitamin D levels below 80 nmol/L.
The 2005 consensus conference concluded that it may be time to increase recommended dietary levels of vitamin D for both the frail elderly and dark-skinned people who get little sun exposure.
Natural dietary sources of vitamin D are few: saltwater fish, cod liver oil, and egg yolks. U.S. guidelines have led to vitamin D fortification of foods, most commonly milk, orange juice, cereal, butter, margarine, and chocolate mixes.
Current U.S. recommendations for daily vitamin D intake call for 200 IU for children and adults up to age 50 years, 400 IU for those aged 51–70 years, and 600–800 IU for those older than 70 years.
“In the past few years there is increasing evidence that these recommendations probably are too low,” Dr. Lim said. One recent study suggested that maintaining sufficient vitamin D levels requires 800–1,000 IU per day of vitamin D3 or 50,000 IU once per month, a dose that's available by prescription only (Photochem. Photobiol. 2005;81:1246–51). Keep in mind that vitamin D intoxication doesn't occur until daily doses exceed 10,000 IU, Dr. Lim said. “Therefore, even at 800–1,000 IU, there is still a significant margin of safety.”
Dr. Lim recommended three sets of articles as helpful references in the ongoing debate about vitamin D:
▸ Results of the 2005 consensus conference: J. Am. Acad. Dermatol. 2005;52:868–76.
▸ A series of seven articles on UV radiation, beginning with one entitled, UV radiation, vitamin D, and human health: an unfolding controversy: Photochem. Photobiol. 2005;81:1243–5.
▸ An overview of the proceedings from the experimental biology 2004 symposium on vitamin D insufficiency: J. Nutr. 2005;135:301–37.