PHOTOPROTECTION AND VITAMIN D

Sunlight is important in the generation of Vitamin D in the skin. In addition to eating foods containing vitamin D, an essential hormone for normal bone development, sunlight exposure also plays a critical role in supplying the human body with its necessary dose of vitamin D (71). Sunlight converts cutaneous stores of 7-dehydrocholesterol (provitamin D3) to previtamin D3 (precholecalciferol) and then to vitamin D3 (cholecalciferol). Vitamin D3 is also the form obtained though ingestion of foods. Once in the body, vitamin D3 is hydroxylated first in the liver to 25-hydroxyvitamin D (25-OHD), and then subsequently hydroxylated again to the active form, 1,25-dihydroxdyvitamin D [1,25-(OH)2D], by the kidneys. It should be noted that 25-OHD is a measure of body stores of Vitamin D.

Because sunlight is considered to be the most important source of vitamin D, there has been concern that photoprotection may, in fact, be contributing to its deficiency. Vitamin D deficiency increases the risk of bone disease, muscle weakness, and possibly certain types of cancer (72,73). In one study, the application of a sunscreen was shown to reduce the skin’s ability to synthesize vitamin D3 (74). 25-hydroxy vitamin D levels have also been shown to be reduced with chronic sunscreen use (75). The active form of vitamin D, 1,25-dihydroxyvitamin D, was shown to be lower in patients using sunscreen compared to a placebo group who did not use sunscreen (76). Although values were lower for the sunscreen group, they still remained within the normal range. However, other studies have reported conflicting findings (77).

Studies of individuals who consistently sustain a lifestyle involving photoprotection have failed to show clinical evidence of vitamin D deficiency. A study of eight xeroderma pigmentosum patients showed that, although 25-OHD levels were low normal, the 1,25(OH)2D levels were normal (78). The lack of seasonal variation in 25-OHD levels showed that the patients received the same amount sunlight (or lack thereof) throughout the year. The evidence provided in this study is supported by epidemiologic studies of sunscreen use, which failed to show that regular sunscreen use led to vitamin D deficiency (79).

Recent media attention to the issue of vitamin D and sunlight reinforces the need for patient education. Although sunlight exposure is important as a source of vitamin D, photoprotection does not result in vitamin D deficiency. Furthermore, the use of tanning beds should not be used as a source of vitamin D. Patients concerned about their vitamin D levels should be encouraged to eat foods rich in vitamin D, such as fish liver oils, egg yolks, and milk fortified with vitamin D or take oral vitamin D supplements.