Quick summer sunbaths make for adequate vitamin D
NEW YORK (Reuters Health) - A few minutes a day of midday summer sun can
raise most fair-skinned people's vitamin D levels to sufficient, but not optimal,
levels, according to new research from the UK.
The skin's production of vitamin D upon exposure to ultraviolet B radiation in sunlight is the body's main source for the nutrient, which is scarce in most foods, Dr. Lesley E. Rhodes of Salford Royal NHS Foundation Hospital in Manchester and colleagues note in their report, which appears in the January 14 online issue of the Journal of Investigative Dermatology.
UK health authorities say "casual exposures to summer sunlight" will allow the body to produce adequate amounts of vitamin D. They also recommend limiting sun exposure beyond a brief amount of time.
To test whether such casual exposures would be enough, the researchers exposed 109 fair-skinned men and women to light equivalent to 13 minutes of midday summer sun three times a week for six weeks. Study participants wore shorts and T-shirts during their brief sun baths.
The study was done during the winter months, when people would be getting very little vitamin D from sunlight, to focus on the effects of the sun baths. All of the study participants had low vitamin D intakes, and none were taking vitamin D supplements.
Participants' average blood level of vitamin D rose from around 18 ng/mL to 28 ng/mL. Recent studies have suggested that 20 ng/mL and above is sufficient, while 32 ng/mL and above is "optimal."
Based on the results, the researchers predicted that with this amount of sun exposure, 90% of white adults in Manchester under the age of 65 would have sufficient vitamin D levels, while 26% would have optimal levels.
The findings don't apply to darker-skinned people, who need longer stretches of sun exposure because their skin color acts as a natural sunblock.
Depending on latitude, the average amount of sun exposure required for similar effects in North America would range from nine to 16 minutes, the researchers say.
"We propose that future public health messages could promote regular short exposures to midday summer sunlight, their duration limited to below the sunburn threshold," the researchers write. But people at high risk of skin cancer should avoid the sun, they add. "Oral supplements may be important in these individuals."
