Gap N2: What is the adequate dose range of vitamin D supplementation? (This Gap is now Closed)
Last Published:  03/26/21 03:33:57 PM (Central)
Responsible Element: Human Health Countermeasures (HHC)
Status: Closed
Closure Rationale
Before 2006 when ISS crews were provided 400 IU vitamin D/day, it was well documented that vitamin D status (25-hydroxyvitamin D) decreased after long-duration space flight (1-4) .  The absence of ultraviolet light during space flight diminishes vitamin D stores in the body, as observed during the 84-d Skylab mission (2) and more recent Mir missions (3, 4) and ISS Expeditions (1).    Despite the reported use of vitamin D supplements by some of the astronauts (average supplement use was 3.0 ± 2.8 per week of a 400 IU vitamin D supplement), the mean serum concentration of 25-hydroxycholecalciferol for the ISS crew members in this study was about 25% less after landing than before launch. 

In 2006, vitamin D recommendations to crews increased from 400 IU vitamin D /day to 800 IU vitamin D /d.  In-flight 25-hydroxyvitamin D data from the Nutritional Status Assessment SMO provide evidence that 800 IU vitamin D/day is enough to maintain vitamin D status during long-duration space flight (Figure 1)(5).  Furthermore, data from the Nutrition SMO experiment show that crewmembers that exercised with the ARED, maintained energy and vitamin D intake during flight maintained bone mineral density during 4-6 month space flights (5).

Several ground-based studies (performed in Antarctica and at the Johnson Space Center) confirm that a vitamin D dose in the range of 800-2000 IU/d is tolerable, safe, and can maintain vitamin D status for 3-6 months even in environments with no UV light exposure (6-8) . This is in line with the recent Institute of Medicine recommendations for vitamin D intake for North Americans (9).  

Figure 1.  Pre- and postflight data from medical operations required testing (protocol MedB8.1) show that vitamin D status decreased after long-duration space flight, despite vitamin D supplementation with 400 IU/d.  In-flight data from SMO showed that 800 IU/d was enough vitamin D3 to maintain status during long-duration space flight.  Red lines depict Institute of Medicine-defined lower acceptable limits (with respect to bone health), and upper advised limit (9).  The green line at 80 nmol/L reflects what many perceive as an optimal level with respect to parathyroid hormone suppression and non-bone health outcomes.

  1. Smith SM, Zwart SR, Block G, Rice BL, Davis-Street JE. The nutritional status of astronauts is altered after long-term space flight aboard the International Space Station. J Nutr 2005;135:437-443.
  2. Leach CS, Rambaut PC. Biochemical responses of the Skylab crewmen: an overview. In: Johnston
    RS, Dietlein LF, eds. Biomedical results from Skylab (NASA SP-377). Washington, DC: National Aeronautics and Space Administration, 1977:204-16.
  3. Smith SM, Wastney ME, Morukov BV, et al. Calcium metabolism before, during, and after a 3-mo spaceflight: kinetic and biochemical changes. Am J Physiol 1999;277:R1-10.
  4. Smith SM, Wastney ME, O'Brien KO, et al. Bone markers, calcium metabolism, and calcium kinetics during extended-duration space flight on the Mir space station. J Bone Miner Res 2005;20:208-18.
  5. Smith SM, Heer MA, Shackelford L, Sibonga JD, Ploutz-Snyder L, Zwart SR. Benefits for bone from resistance exercise and nutrition in long-duration spaceflight: evidence from biochemistry and densitometry. J Bone Miner Res 2012;27:1896-1906.
  6. Smith SM, Gardner KK, Locke J, Zwart SR. Vitamin D supplementation during Antarctic winter. Am J Clin Nutr 2009;89:1092-8.
  7.  Zwart SR, Parsons H, Kimlin M, Innis SM, Locke JP, Smith SM. A 250 µg/week dose of vitamin D was as effective as a 50 µg/d dose in healthy adults, but a regimen of four weekly followed by monthly doses of 1250 µg raised the risk of hypercalciuria. Br J Nutr 2013:1-7.
  8.  Zwart SR, Mehta SK, Ploutz-Snyder R, et al. Response to vitamin D supplementation during Antarctic winter is related to BMI, and supplementation can mitigate Epstein-Barr virus reactivation. J Nutr 2011;141:692-7.
  9. Institute of Medicine. Dietary reference intakes for calcium and vitamin D. Washington, DC: National Academies Press, 2011.



Two studies conducted in Antarctica, 1 vitamin D dosing study completed at JSC, and in-flight data from the Nutrition SMO have contributed to a body of evidence that shows 800 IU vitamin D3/day during a 6-month spaceflight is adequate to maintain vitamin D status.
Target for Closure
No Target for Closure available.
Risk Risk of Performance Decrement and Crew Illness Due to Inadequate Food and Nutrition
You are here! Gap N2: What is the adequate dose range of vitamin D supplementation? (This Gap is now Closed)

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