National report — Results of a study assessing sunlight exposure during winter months in various geographic locations across the United States refute the idea that "safe sun" photoprotection practices are associated with a risk of vitamin D deficiency, says J. Frank Nash, Ph.D., principle scientist, Procter & Gamble Co., Cincinnati.
National report - Results of a study assessing sunlight exposure during winter months in various geographic locations across the United States refute the idea that "safe sun" photoprotection practices are associated with a risk of vitamin D deficiency, says J. Frank Nash, Ph.D., principle scientist, Procter & Gamble Co., Cincinnati.
The investigation enrolled 92 women ages 30 to 45 years old who were asked to keep a diary of time spent in the sunlight over a one-week period during the winter. Those data together with UV meter measurements of erythemically weighted flux of sunlight in each study area were used to calculate the average daily dose of UV. Then, levels of skin-generated vitamin D synthesis with and without use of an SPF 15 sunscreen were determined using the formula of Holick (The Lancet 2001:357:4-6) and assuming sunscreen application was optimal.
Based on these data, even in the area where average daily sunlight exposure was lowest, women would still be expected to achieve the recommended daily adequate intake for vitamin D through the combined contributions of cutaneous synthesis and dietary sources, reports Dr. Nash.
The five sites where data on sunlight exposure were collected included two cities where there was a high fluence of UV - Plantation/Fort Lauderdale, Fla., and La Jolla, Calif.; two northern cities - Chicago and New York; and a popular winter ski destination - Vail, Colo. With the exception of Chicago, where the diary entries were made Jan. 4 through 10, the recording period for the other study locations was March 1 through 7.
After enrollment, all women were thoroughly instructed about accurate documentation of time spent in the sun. Analysis of their diaries showed the average time spent in the sun ranged from 29 minutes to 70 minutes per day. The average daily doses of erythemically weighted solar UV ranged from 16.7 to 79.2 mJ/cm2.
Applying the Holick formula (1 minimal erythemal dose (MED) = 10,000 IU vitamin D for full-body exposure), it was determined that for face and hand exposure, those UV doses would result in vitamin D synthesis by the skin in amounts ranging between 1,336 and 6,344 IU. Assuming that an SPF15 sunscreen would reduce UV skin absorption by 93 percent, it was calculated that vitamin D synthesis across the five study sites would range from 88 to 424 IU/ day. According to recommendations from the Institute of Medicine, daily adequate intake of vitamin D for males and females ranges from 200 to 600 IUs, depending on age.
Intake adequate "There is a whole field of study looking at vitamin D dietary intake and health effects. In one of the most recent surveys by Moore et al. (J Am Diet Assoc 2004:104:980-983), even teenage females, whose intake levels were among the lowest, were still getting about half the recommended adequate intake through food sources and dietary supplements.
"Being conservative and expecting those individuals had the minimum average sun exposure level found in our study, they would still meet the recommendations for vitamin D intake. In reality, 'sun safety,' including the daily use of broad spectrum SPF 15 sunscreens together with a balanced diet and, if necessary, vitamin supplements, should provide the best of both worlds," Dr. Nash says.
Disclosure: The research Dr. Nash reported was funded by P&G Beauty.