Effect of vitamin D supplementation and ultraviolet B exposure on serum 25-hydroxyvitamin D concentrations in healthy volunteers: a randomized, crossover clinical trial

Br J Dermatol. 2013 Aug;169(2):434-40. doi: 10.1111/bjd.12349.


Background: Solar ultraviolet (UV) radiation during the summer and vitamin D supplementation are two major sources of vitamin D for humans at northern latitudes. However, little is known about the relative efficiency of these two vitamin D sources.

Objectives: The main goal was to compare the efficiency of high-dose oral vitamin D3 supplementation (2000 IU per day for 30 days) with a simulated summer UV exposure [10 sunbed sessions to a total dose of 23·8 standard erythema doses (SED)] to improve vitamin D status.

Methods: Healthy volunteers were randomized into two groups: group 1 received vitamin D supplementation followed by 10 whole-body sunbed exposures; group 2 started with 10 sunbed exposures followed by vitamin D supplementation.

Results: The oral supplementation with vitamin D3 resulted in a mean (SEM) serum 25-hydroxyvitamin D [25(OH)D] increase of 25·3 (5·4) nmol L(-1) . A similar increase, 19·8 (5·4) nmol L(-1) , was observed after simulated summer UV exposure. At the end of the study, serum 25(OH)D concentrations were similar in both groups.

Conclusions: Twice-weekly whole-body sunbed exposure to a dose of 4·8 SED is equal to 2000 IU daily of oral vitamin D supplementation for 30 days and enough to achieve and maintain serum 25(OH)D concentrations > 75 nmol L(-1) in ~55% of cases. Based on our calculations, this dose corresponds to a cumulative weekly whole-body exposure of 3·4 SED (~ 40 min around midday during the summer at the latitude of Oslo).

Publication types

  • Comparative Study
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Administration, Oral
  • Adult
  • Cross-Over Studies
  • Dietary Supplements
  • Dose-Response Relationship, Drug
  • Dose-Response Relationship, Radiation
  • Female
  • Healthy Volunteers
  • Humans
  • Male
  • Middle Aged
  • Seasons
  • Sunlight
  • Ultraviolet Rays*
  • Vitamin D / administration & dosage*
  • Vitamin D / analogs & derivatives*
  • Vitamin D / metabolism
  • Vitamins / administration & dosage*
  • Young Adult


  • Vitamins
  • Vitamin D
  • 25-hydroxyvitamin D