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Vitamin D supplementation during Antarctic winter

¹ From the Space Life Sciences Directorate, National Aeronautics and Space Administration Johnson Space Center, Houston, TX (SMS and JL); the UCLA School of Medicine and VA Greater Los Angeles Health Care System, Los Angeles, CA (KKG); and the Universities Space Research Association, Houston, TX (SRZ).

² Supported by the NASA Human Research Program and made possible by the National Science Foundation.

³ Address reprint requests and correspondence to SM Smith, NASA Johnson Space Center, Mail Code SK3, 2101 NASA Parkway, Houston, TX 77058. E-mail: scott.m.smith{at}nasa.gov.

Background: Persons with limited exposure to ultraviolet B light, including space travelers, may not receive enough vitamin D. Recent studies indicate that optimal serum 25-hydroxyvitamin D [25(OH)D] should be 80 nmol/L.

Objective: This study was designed to evaluate the effectiveness of 3 doses of vitamin D to raise and maintain 25(OH)D to a concentration >80 nmol/L in persons with limited ultraviolet B light exposure.

Design: This was a 5-mo, prospective, randomized, double-blind study of vitamin D supplementation. It was conducted during winter in Antarctica at the McMurdo Station, when ultraviolet B radiation levels are essentially zero. The 55 subjects were randomly divided into 3 groups for vitamin D supplementation: 2000 IU/d (n = 18), 1000 IU/d (n = 19), and 400 IU/d (n = 18). An additional 7 subjects did not take supplements or took supplements of their own choosing. Blood samples were collected about every 2 mo during the winter.

Results: About 5 mo after supplementation started, 25(OH)D increased to 71 ± 23 nmol/L in the 2000-IU/d group, 63 ± 25 nmol/L in the 1000-IU/d group, and 57 ± 15 nmol/L in the 400-IU/d group and decreased to 34 ± 12 nmol/L in the group not taking supplements.

Conclusions: These data will enable us to provide space crews with evidence-based recommendations for vitamin D supplementation. The findings also have implications for other persons with limited ultraviolet light exposure, including polar workers and the elderly.