The Use of Sunscreen and the Risk of Vitamin D-Deficiency Rickets In the 1990's Stanley Zlotkin MD, PhD, and Veena Guru Skin cancer rates have steadily increased in North America over the past twenty years. The thinning of the ozone layer is believed to be at least partially responsible for this increase. With widespread recognition of a "sun is harmful" message, it is not surprising that sunscreen use is rapidly increasing and exposure to ultraviolet radiation is decreasing. Because exposure to ultraviolet-B (UV-B) radiation is required for the endogenous synthesis of vitamin D, the combination of sunscreen use and sun avoidance may increase the risk of vitamin D deficiency. This review will consider the health and nutritional effects of exposure to UV-B radiation and sunscreen use in infants and children. It will also highlight their potential effects on vitamin D metabolism. It is the midband or UV-B spectrum of UV emitted from the sun which is primarily responsible for its carcinogenic effects. Since the same UV-B rays that produce vitamin D in the skin, are also associated with adverse effects on the skin, excessive exposure time, even for vitamin D synthesis, is potentially harmful. The skin damage caused by UV-B is thought to be cumulative. Malignant melanoma, as well as basal and squamous cell carcinomas (nonmelatoma skin cancer) have been directly linked to skin exposed extensively to the sun. The risk of nonmelatoma skin cancer is more than proportional to the increase in UV-B exposure 1. Public health advice has appropriately stressed that skin should be shielded from the sun from birth onwards, especially in light-skinned individuals, although the risk of nonmelatoma skin cancer is not only limited to those with extremely sensitive skin. With enough exposure, even a dark-skinned subject who rarely burns is at a substantial risk for nonmelanomatus carcinoma 2. It takes several years, however, for the effects of solar exposure to become evident. Thus, sun avoidance and protection are most important in early years. Protection from UVB Exposure A number of exogenous and endogenous factors work interactively to increase or decrease UVB exposure. These factors include geo-latitude, season of the year, time of day (the highest UV-B levels occur between the hours of 10:00 and 13:00), weather (cloud cover, rain), altitude (more UV-B exposure at higher altitudes), air pollution, surrounding environment (concrete, sand, water and snow reflect UV-B rays, while grass absorbs them), area of skin exposed, clothing and sunscreen use 3. Skin type also has a significant effect on the risk of sun burn and the rate of cutaneous synthesis of vitamin D 3. Skin is pigmented by melanin which acts as a natural sunscreen. Fair skinned individuals, for example, have been shown to produce six times more vitamin D than dark skinned people exposed to similar UVB levels. Sunscreens block the absorption of UV-B which is the same radiation required for cutaneous synthesis of vitamin D 5. There are two major classes of sunscreens: one provides a physical barrier to solar radiation and the other contains agents which absorb specific portions of the UV spectrum. Barrier sunscreens contain substances which scatter and reflect light. They are more suited to infants, as there is less chance of causing a contact or hypersensitivity reaction. "Absorbing" sunscreens contain PABA, PABA esters or anthranilates. These sunscreens tend to be colorless after application to the skin and therefore are more cosmetically acceptable than barrier screens. They are, however, more likely to cause irritation on contact, allergic, or other skin reactions 5. A sunscreen with a SPF factor of 30 only allows 1/30th of the ultra violet rays to penetrate the skin. It is not surprising, therefore, that regular use of sunscreens has been associated with low body stores of vitamin D. With the increasing use of sunscreen and avoidance of sun exposure one may justifiably ask whether infants and children are at an increased risk of vitamin D deficiency. Rickets in Northern Countries In northern countries, including Canada and parts of continental USA, supplemental vitamin D may be required for optimal bone mineralization and growth in length in infants 6. In Finland, a country with scant sunlight in winter due to its northern latitude, very low 25 (OH) Vitamin D levels were detected in exclusively breast fed infants without supplementation 7. Similar results were seen in infants from Norway 8. In both countries, a vitamin D supplement of 400 IU per day was found to protect the infants from biochemical vitamin D deficiency. Despite recommendations for vitamin D supplementation of breastfed infants in North America, vitamin D deficiency rickets still exists in Canada today. Forty-eight cases of rickets were reported in children between 1977 and 1984 in a native community north of Winnipeg 9. The cause of the rickets was a combination of lack of dietary vitamin D and very limited sun exposure. The mothers of the children were also found to be deficient in vitamin D. Six cases of nutritional rickets were recently reported in Vancouver 10. Two were fair skinned and four were dark. All had minimal exposure to sunlight. Five of the six were breast fed, while the sixth had been weaned one month prior to diagnosis to a non-vitamin D containing beverage. In Toronto, 17 cases were described between 1988 and 1993 11. The diagnosis was made at 7 to 33 months of age. All children were symptomatic with typical biochemical and physical signs of rickets. All of the children had dark skin and had been exclusively breast fed with no vitamin D supplementation and little or no sunlight exposure. Summary These surveys clearly demonstrate that the three important variables influencing an infant's vitamin D status are: what they are fed, where they live and their degree of skin pigmentation. Exclusive breast feeding is not a good source of vitamin D. Perhaps more importantly, the further north an infant lives, the less likely it will be that they will synthesize enough vitamin D during the summer months to maintain adequate stores through the winter. A new variable, not previously considered is the effect of extensive sun block use on preventing cutaneous vitamin D synthesis. Thus if recommendations for sun block use are followed, assurance of an adequate dietary source of vitamin D becomes critical, especially for breastfeeding infants. References: I. Stem RS, Weinstein MC, Baker SG. Risk Reduction for Nonmelanoma Skin Cancer With Childhood Sunscreen Use. Arch Dermatol 122:537-545, 1986. 2. Vitaliano PP, Urbach F. The Relative Importance of Risk Factors in Nonmelanoma Carcinoma. Arch Dermatol 116:454-456, 1980. 3. Environment Canada: UV and You, Living with Ultraviolet. 4. Clemens TL, Adams JS, Holick MF, et al. Increased Skin Pigment Reduces the Capacity of Skin to Synthesize Vitamin D 3. Lancet 74-76, Jan. 9, 1982. 5. Matsuoka LY, Wortsman J, et al. Chronic Sunscreen Use Decreases Circulating Concentrations of 25(OH)D Arch Dermatol 124:1802-1804, 1988. 6. Greer FR, Searcy J, Levin R, et al. Bone mineral Content and Serum 25-hydroxyvitamin D Concentrations in Breast-fed Infants with and Without Supplemental Vitamin D: One-year follow-up. Pediatr 100:919-922, 1982. 7. Ala-Houbala M. 25-Mydroxyvitamin D Levels During Breast-Feeding With or Without Maternal or Infantile Supplementation of Vitamin D. J Pediatr Gastroenterol Nutr 4:220-226, 1985. 8. Markestad T. Effect of Season and Vitamin D Supplementation on Plasma Concentrations of 25-Hydroxyvitamin D in Norwegian Infants. Acta Paediar Scand 72:817-821, 1983. 9. Haworth JC, Dilling LA. Vitamin-D-deficient Rickets in Manitoba l972-84. Can Med Assoc J 134:237-241, 1986. 10. Kristensen K, Daaboul J, Tze W. Nutritional Rickets in Infants Breast fed by Vitamin D Deficient mothers. J Can Diet Assoc 55:7-8, 1994. 11. Binet A, Kooh SW. Persistence of Vitamin d-deflciency Rickets in Toronto in the 1990's. Can J Public Health 87:227-30, l996.
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