Their conclusion was reached after data on the relationship between sunlight, tanning booths and vitamin D was reviewed at a conference convened by the American Academy of Dermatology Association. The findings are contained in a white paper published in the May 2005 issue of the Academy's journal.
Vitamin D helps maintain normal blood levels of calcium and phosphorus, thereby helping to improve bone and muscle health, reducing older people's risk of falling and preventing fractures. Recommended intake is 200 international units per day (IU/d) for young adults, 400 IU/d for those aged 51 to 70 years, and 600 IU/d for those over age 70.
Natural dietary sources include milk, egg yolk, oily fish and liver, and several studies have indicated that most normal people derive adequate amounts of vitamin D from incidental sun exposure, without the need to intentionally court the sun's rays.
However, the conference drew attention to increasing evidence that some sectors of the population, particularly older adults and darker-skinned people, may not glean the vitamin D they need from incidental exposure or diet, leading to a deficiency that could have serious health consequences.
"When people age, their skin becomes less equipped to process vitamin D absorption through incidental sun exposure," said Dr Vincent DeLeo, associate professor of clinical dermatology at Columbia University.
He also explained that melanin, a natural substance that is more prolific in darker skin, reduced the skin's ability to photosynthesize vitamin D. While it has been estimated that for individuals with skin phototype II (fairer-skinned) five minutes of noontime summer sun exposure two-to-three times per week is more than adequate to satisfy the body's requirement for vitamin D, darker-skinned people would need more exposure to produce the same results.
But if older and darker-skinned people seek to boost their intake by lying out in the sun or undergoing artificial tanning, they place their health at even greater risk.
"Under no circumstances should anyone be misled into thinking that natural sunlight or tanning beds are better sources of vitamin D than foods or nutritional supplements. The only thing they are proven to be better at is increasing your risk of developing skin cancer," said Dr DeLeo.
"Skin cancer is an epidemic in this country and recommending increased UV exposure with claims that sunlight somehow promotes good health is highly irresponsible."
It is estimated that 105,750 people in the United States will be diagnosed with melanoma, the most serious form of skin cancer, in 2005 - a ten percent increase on last year's statistics. If this incidence rate continues, one in five Americans will develop skin cancer during their lifetime.
An estimated 7,770 Americans will die from the disease this year.