DAVIS, Calif.—Vitamin D recommendations are way too low, according to researchers from University of California, Davis (J Nutr. 2010 Jan 6). Results of the study found those with lighter skin (European ancestry) and high sun exposure need 1,300 IU/d of vitamin D in the winter; and darker-skinned individuals (African ancestry) with low sun exposure need from 2,100 to 3,100 IU/d year round. The current dietary reference intake (DRI) for vitamin D from the Institutes of Medicine (IOM) is 200 IU/d.
Researchers examined the effects of sun exposure, vitamin D intake and skin pigmentation on serum 25-hydroxyvitamin D (25[OH]D) in young adults with a wide range of skin pigmentation and sun exposure. Four cohorts of participants (n = 72 total) were studied for 7 to 8 weeks in the fall, winter, spring and summer in Davis, CA (38.5° N, 121.7° W, Elev. 49 ft). Skin reflectance was measured using a spectrophotometer, vitamin D intake using food records, and sun exposure using polysulfone dosimeter badges. A multiple regression model (R2 = 0.55; P < 0.0001) was developed and used to predict the serum 25(OH)D concentration for participants with low [median for African ancestry] and high [median for European ancestry] skin reflectance and with low [20th percentile, 20 min/d, 18 percent body surface area exposed] and high (80th percentile, 90 min/d, 35 percent body surface area exposed) sun exposure, assuming an intake of 200 IU/d.
Predicted serum 25(OH)D concentrations for African ancestry individuals with low and high sun exposure in the winter were 24 and 42 nmol/L respectively and in the summer were 40 and 60 nmol/L. Corresponding values for European ancestry individuals were 35 and 60 nmol/L in the winter and in the summer were 58 and 85 nmol/L. To achieve 25(OH)D 75 nmol/L, researchers estimated European ancestry individuals with high sun exposure need 1,300 IU/d vitamin D intake in the winter and African ancestry individuals with low sun exposure need 2,100 to 3,100 IU/d year-round.