A recent study shows that at least 2,000 International Units (IU) of vitamin D3 are required to ensure adequate serum 25-hydroxyvitamin D (25(OH)D) levels of this vitamin in the blood.
Researchers from the Winthrop University Hospital, Mineola, New York carried out a three-year experiment with 208 healthy post-menopausal African-American women. Half of the women were randomly assigned to consume a daily placebo and the other half took 20 ìg/d of vitamin D (800 IU) for two years, followed by 50 ìg /d (2,000 IU) for another year.
Vitamin D3 is produced in the skin when exposed to sunlight. However, dark skin reduces the effect of UVB radiation and that in turn would make darker-skinned people more at risk of vitamin D deficiency.
As much as 4000 IU per day may be required for individuals who are already deficient in the vitamin. The current recommended daily allowance of Vitamin D is 10 to 15 μg (400-600 IU).
Source: MedPage Today, December 07, 2007; Sonia T et al “Dose response to vitamin D supplementation among postmenopausal African American women” American Journal of Clinical Nutrition (December 2007) 86(6):1657-1662
Chapter: Vitamins :: 4 January 2008