The Role of Sunlight
Vitamin D intake—are children and pregnant women getting as much as they used to?
No, because sun exposure is much less common today. Furthermore, perhaps because the term vitamin D contains the word "vitamin," many people mistakenly assume it is a vitamin. Vitamin D is the only known precursor for a steroid hormone system that, until recent sun-avoidance, always began in the skin, not the mouth. Before the sun-scare, 90% of human vitamin D stores came from skin production, not diet. Large populations of pregnant women and autistic children ingesting small amounts orally, instead of generating large amounts through the skin, are novel to human brain development. Poskitt EM, Cole TJ, Lawson DE. Diet, sunlight, and 25-hydroxyvitamin D in healthy children and adults. Br Med J. 1979 Jan 27;1(6158):221–3. Holick MF. Photosynthesis of vitamin D in the skin: effect of environmental and life-style variables. Federation Proceedings 1987; 46:1876–1882.
Obviously, if people are going to put it in their mouths rather than make it in their skin, oral intake must be adequate enough to make up for decreased skin production. However, the skin's production of vitamin D is rapid and robust, easily exceeding usual dietary sources by a factor of 10. For example, when fair-skinned adults sunbathe in the summer (one full-body exposure to ultraviolet light, enough to turn the skin slightly pink) they make about 20,000 units of vitamin D in 20 minutes. A pregnant woman would have to drink 200 glasses of milk or take 50 prenatal multivitamins to do the same. An autistic boy who plays inside the house, instead of outside, would have to take several thousand units of vitamin D to make up for what his skin would have produced had he played outside that day. Holick MF. High prevalence of vitamin D inadequacy and implications for health. Mayo Clinic Proceedings 2006; 81: 297–299. Hollis BW. Circulating 25-hydroxyvitamin D levels indicative of vitamin D sufficiency: implications for establishing a new effective dietary intake recommendation for vitamin D. J Nutr. 2005 Feb;135(2):317–22.
In 1989, around the time autism began to rise, the American Medical Association's (AMA) Council on Scientific Affairs first warned about the dangers of sun exposure, advising mothers to "keep infants out of the sun as much as possible." In 1999, when autism rates really exploded, the American Academy of Pediatrics went further, advising mothers always to keep infants out of direct sunlight, use sun-protective clothes and sunblock, and make sure children's activities minimize sunlight exposure. Quite inexplicably, they said there was "no evidence" such "rigorous sun protection" would affect vitamin D levels. By 2002, the Centers for Disease Control (CDC) reported such efforts were quite successful: "protection from sun exposure is reported for a high proportion of children." Guercio-Hauer C, Macfarlane DF, Deleo VA. Photodamage, photoaging and photoprotection of the skin. Am Fam Physician. 1994 Aug;50(2):327–32, 334. No authors listed. Harmful effects of ultraviolet radiation. Council on Scientific Affairs. JAMA. 1989 Jul 21;262(3):380–4. Hall HI, et al. Protection from sun exposure in US white children ages 6 months to 11 years. Public Health Rep. 2001 Jul–Aug;116(4):353–61.
Medical organizations did not plan for the vitamin D deficiency such sun avoidance would predictably induce. For example, when the AMA warned about the dangers of sunlight, they did not even mention that sunlight triggers the formation of vitamin D. Furthermore, medical recommendations for infants, children, young women, and pregnant women, did not change during the decades of sun avoidance: 200 units/day for all infants, children, pregnant women, and young adults—regardless of weight. That is, they did, and still do, recommend the same 200 daily units for a 5-pound infant as they do for a 200-pound pregnant woman. In fact, in 2003, the American Academy of Pediatrics cut their long-standing 400 units/day recommendation in half—apparently to comply with government recommendations—and did so despite warnings from a prominent University of Wisconsin professor of pediatrics, Dr. Frank Greer, and despite their own advice 4 years earlier that infants and children should avoid sunlight. Greer FR. Issues in establishing vitamin D recommendations for infants and children. Am J Clin Nutr. 2004 Dec;80(6 Suppl):1759S–62S.
Yes they have, although no linear studies of vitamin D levels over the last 20 years exist. That is, we don't know how successful sun avoidance campaigns have been in lowering vitamin D levels. However, if one assumes that some Americans do follow their government's and physician's advice, then at least some must have had declining vitamin D levels over the last 20 years—unless they took enough supplemental vitamin D to make up for lack of sun exposure. Unfortunately, few take the thousands of daily units needed to do that. What we do know is that vitamin D deficiency, like autism, is now an epidemic. Holick MF. The vitamin D epidemic and its health consequences. J Nutr. 2005 Nov;135(11):2739S–48S.» page: autism index 1 2 3 4 5 6 7 8 9 10 11