Vitamin D Supplementation and Sunlight Exposure on Serum Vitamin D Concentrations in 2 Parallel, Double-Blind, Randomized, Placebo-Controlled Trials

Background: Vitamin D concentrations are a function of sunlight exposure and dietary intake. However, current dietary vitamin D recommendations do not consider differences in country-specific sunlight availability or spontaneous individual exposure. Objectives: We aimed to investigate the effects of vitamin D supplementation and sunlight exposure on vitamin D concentrations in Brazilian women living in high compared with low latitudes. Methods: In 2 parallel, double-blind, randomized placebo-controlled trials, Brazilian women living in England (51 degrees N) composed "without ultraviolet B (UVB) exposure" groups and those living in Brazil (16 degrees S) composed the "with UVB exposure" groups (mean age, 31.39 +/- 8.7 years). Participants received 15 mu g cholecalciferol or placebo daily for 12 weeks during wintertime. Serum 25-hydroxyvitamin D [25(OH)D] concentrations, the primary outcome, were assessed by HPLC-MS/MS, vitamin D intakes were assessed by 4-day diet diaries, and sunlight exposure was assessed by UVB dosimeters. The effects of supplementation and UVB exposure were tested by the intention to treat with a linear mixed model. Results: The 25(OH)D concentrations increased in both supplemented groups [from 75.1 +/- 22.0 to 84.8 +/- 21.0 nmol/L (P = 0.004) in the group with UVB exposure; from 38.1 +/- 15.9 to 55.1 +/- 12.2 nmol/L (P < 0.001) in the group without UVB exposure], with no significant changes in either placebo group. Concentrations in both supplemented groups were higher than those in the placebo group without UVB exposure (P = 0.0002 in the group with UVB exposure; P = 0.0035 in the group without UVB exposure). Postintervention 25(OH)D concentrations were significantly affected by serum 25(OH)D concentrations at baseline (P < 0.0001) and by intervention (placebo or supplement; P > 0.0001), with a large effect size (Cohen's D = 0.768), but were not affected by UVB exposure (with or without; P = 0.1386), nor by the interaction between the intervention (placebo or supplement) and UVB exposure (with or without; P = 0.9845). Conclusions Moderate supplementation of 15 ug/d cholecalciferol, in accordance with current recommendations, supports an adequate vitamin D status in adult women, irrespective of latitude, and might concomitantly prevent an increase in parathyroid hormone.