• Yu Mi Lee, Se A Kim, and Duk Hee Lee.
• Department of Preventive Medicine, School of Medicine, Kyungpook National University, Daegu, Korea.
• J. Korean Med. Sci. 2020 Mar 2; 35 (8): e50.

BackgroundLack of sunlight exposure is the primary reason for the worldwide epidemic of vitamin D deficiency. Although recommended sunlight exposure guidelines exist, there is no evidence regarding whether current guidelines are optimal for increasing vitamin D levels among individuals with vitamin D deficiency.MethodsSixty Korean adults aged 20-49 years with serum 25-hydroxyvitamin D (25[OH]D) levels of < 20 ng/mL were randomly assigned to three groups: sunlight exposure (n = 20), vitamin D supplementation groups (n = 20), and daily living (n = 20) for 1 month. The sunlight exposure group had sunlight exposure on 20% to 30% of their body surface areas for 30-60 minutes per day, 3 times a week during the summer season. Vitamin D supplementation was prescribed with 800 IU/day of vitamin D. The serum levels of 25(OH)D were measured at baseline and at 1-month follow-up examinations.ResultsThe largest change in serum 25(OH)D was observed among the vitamin D supplementation group (+3.5 ng/mL, P < 0.001). The sunlight exposure group showed a slight increase in serum 25(OH)D level, but the absolute increase was less than one-third that of the vitamin D supplementation group (+0.9 ng/mL, P = 0.043). Only two participants in the sunlight exposure reached serum concentrations of 25(OH)D ≥ 20 ng/mL at follow-up. The daily living group showed no difference in vitamin D levels (-0.7 ng/mL, P = 0.516).ConclusionSunlight exposure was not sufficient to overcome vitamin D insufficiency or deficiency in the current study subjects. Effectiveness of current sunlight exposure guidelines among various populations should be reassessed in larger clinical studies.Trial RegistrationClinical Research Information Service Identifier: KCT0002671.© 2020 The Korean Academy of Medical Sciences.

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