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February 2013

Serum Vitamin D Levels May Vary After Supplementation

A recent study investigated how serum vitamin D levels change over time after supplementation.

The major biologic function of vitamin D is to maintain normal blood levels of calcium and phosphorus. Vitamin D has several different forms. Vitamin D2 (ergocalciferol ) and D3 (cholecalciferol) are two of the most common forms taken as supplements. The time for vitamin D levels to peak in the serum is variable, depending on the form.

Serum 25-hydroxyvitamin D [25(OH)D] is the currently accepted measure for vitamin D levels. Blood concentrations of greater than 50 nanomoles per liter are considered sufficient. Levels of higher than 125 nanomoles per liter may be associated with adverse effects.

In the recent study, 34 non-pregnant and 27 pregnant women received a single dose of Vitamin D3 (70,000 IU). Participants gave blood and urine samples for ten weeks after supplementation.

Analysis showed that serum 25-hydroxyvitamin D [25(OH)D] increased in the first week after supplementation. Generally, 25(OH)D peaked within the three weeks after the initial dose of vitamin D. However, there was substantial variability in participant 25(OH)D. While some women had a clear peak in 25(OH)D within the first week, other women had fluctuating 25(OH)D levels without a clear peak.

These results were similar in both the non-pregnant and pregnant women. A lack of adverse effects was observed from vitamin D supplementation.

For more information about vitamin D supplementation, please visit Natural Standard's Foods, Herbs & Supplements Database.


  1. Natural Standard: The Authority on Integrative Medicine. 
  2. Roth DE, Al Mahmud A, Raqib R et al. Pharmacokinetics of a single oral dose of vitamin D3 (70,000 IU) in pregnant and non-pregnant women. Nutr J. 2012 Dec 27;11:114. 

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