EFFECT OF SERIAL UV-B EXPOSURE ON VITAMIN D METABOLITES IN HUMAN MILK AND FORMULA FED INFANTS. † 1865

Human milk is known to be a poor source of vitamin D, and infants who are sunshine deprived and exclusively fed human milk without vitamin D supplementation may be at risk for developing vitamin D deficient rickets. Previous studies have shown recorded degree of sunshine exposure to be the single most predictive factor in vitamin D status in human milk-fed infants. Skin converts 7-dehydrocholesterol to previtamin D₃ and then vitamin D₃. From skin, vitamin D₃ is transported to the liver for metabolism to 25 hydroxyvitamin D₃ (25OHD). No direct studies of ultraviolet B radiation (UV-B) exposure in infants has been done. We hypothesized that UV-B exposure would raise serum 250HD in human milk-fed infants but have little effect in formula fed infants. Methods: We examined the direct effect of UV-B radiation in six healthy. term, Caucasian infants; four were exclusively human milk-fed, and two formula-fed (vitamin D 400 IU /L); infants underwent a series of six subminimal erythemal doses(sub-MED) of UV-B. Human milk-fed infants were not supplemented with vitamins or formula prior to or during study. Amount of UV-B was 80% of MED in fair skinned adults and children. Blood was obtained just prior to UV-B and 3 days following final UV-B. Serum 25(OH)D₂ and D₃, vitamin D₂ and D₃, 1,25(OH)₂D were determined. Results: Baseline vitamin D₃ and 25(OH)D₃ were substantially lower in human milk compared with formula-fed infants (table). There was a significant rise in vitamin D₃ and 25(OH)D₃ following UV-B in human milk fed infants, bringing levels up to formula-fed levels(table). Formula-fed levels of vitamin D₃ and 25(OH)D₃ did not change following UV-B. Vitamin D₂, 25(OH)D₂ levels were undetectable in all infants, and 1,25(OH)₂D levels were not significantly altered by therapy. Conclusions: Human milk-fed infants have low vitamin D status in winter and there is a clear serum vitamin D metabolite response to UV-B exposure; following exposure to UV-B, these levels approach those of formula-fed infants which are adequate by adult and childhood standards.

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