Sun exposure not so bright

June 1, 2006

National report - A recommendation for intentional sunexposure to achieve adequate vitamin D levels is inappropriate,according to Henry W. Lim, M.D.

National report - A recommendation for intentional sun exposure to achieve adequate vitamin D levels is inappropriate, according to Henry W. Lim, M.D.

"Although less than adequate serum vitamin D levels are a problem in some individuals, vitamin D sufficiency can be achieved in others through incidental sun exposure, dietary intake and with vitamin supplements. Therefore, in my opinion, we should recommend that individuals at risk for vitamin D insufficiency be encouraged about appropriate dietary intake and use of a vitamin D3 supplement, and I am certain that with sensible photoprotection, we should be able to protect our skin, maintain our general health and be able to go out and enjoy life."

How much is enough?

Current dietary reference intake standards in the United States recommend that children and adults up to age 50 receive 200 iu of vitamin D daily. For adults ages 51 to 70 years, the recommendation is 400 iu per day, and it increases to 600 to 800 iu/day for older individuals.

"However, there is increasing evidence that these recommendations are too low, and authors of a recent article concluded that 800 to 1,000 iu per day or 50,000 iu once a month was needed to maintain vitamin D sufficiency. Since vitamin D3 intoxication occurs when the oral daily dose exceeds 10,000 iu, there is still a significant margin of safety with this recommended increased intake," Dr. Lim tells Dermatology Times.

Sampling the sources

The only avenues for acquiring vitamin D naturally are by sun exposure and through a very limited number of dietary sources.

Therefore, in the United States, the government has recommended vitamin D2 fortification of certain foods, including milk, orange juice, margarine, butter, cereals and chocolate mixes.

Vitamin supplements provide a third source of vitamin D. Those products contain vitamin D2 or D3. Vitamin D2 is found most commonly, but D3, which is produced in the skin and found in the natural food sources, is preferred.

Controversial connections

The associations between vitamin D and health and disease represent an area of much debate.

Available epidemiologic studies indicate vitamin D has important benefits for maintaining bone mineral density, improving lower extremities strength and reducing risks for fractures, falls and colorectal cancer. Relationships between vitamin D and many other diseases have been postulated, but not proven in a valid scientific study, Dr. Lim says.

He also points out that two recent articles published in the New England Journal of Medicine have created significant controversy regarding the effect of vitamin D3 on fracture and colorectal cancer risk. Those papers reported outcomes from cohorts of greater than 36,000 postmenopausal women participating in the Women's Health Initiatives trial. After seven years of follow-up, there were no significant differences in hip fracture rate, incidence of colorectal cancer or tumor characteristics between women who received vitamin D3 400 iu plus elemental calcium 1 g daily versus placebo-treated controls.

"However, as described in editorials accompanying these articles, these studies had some major limitations that need to be considered when interpreting the results," Dr. Lim says.

Factors impeding natural synthesis

Concern that photoprotection contributes to vitamin D insufficiency is particularly linked to a laboratory study conducted by Michael Holick, M.D., Ph.D., and colleagues reporting significant suppression of vitamin D3 synthesis among subjects who applied an SPF-8 sunscreen prior to being exposed to one minimal erythema dose of simulated sunlight.