Written by Susan Sweeny Johnson, PhD, Biochem.
Vitamin D plays a crucial role in dietary calcium absorption and maintenance of blood calcium levels, both of which have a direct effect on bone health. Recent studies show that vitamin D may help prevent colon cancer1 and diabetes2 among other things.
The Food and Nutrition Board’s (FMB’s) current upper limit of vitamin D3 of 50 ìg per day (2000 IU) was calculated based on 10-year old data. Researchers reviewed the most recent vitamin D studies to determine if the current upper limit should be raised in order to get the most benefit out of vitamin D supplementation.
In order to do this, they compared the results of more than 20 individual studies involving vitamin D3 supplementation. They gave preference to studies where the amount of vitamin D3 supplementation was correlated with 25-hydroxyvitamin D and calcium blood concentrations. Hypercalcemia, measured by elevated blood calcium, was selected as the measure of vitamin D toxicity. Hypercalcemia’s clinical manifestations include pain, conjunctivitis, anorexia, fever, chills, thirst, vomiting, and weight loss.
The researchers recommended raising the upper limit for vitamin D supplementation to 250ìg per day (10,000 IU). At this supplementation level, blood calcium is not elevated. In fact, over 1200ìg per day is necessary to achieve hypercalcemia. Sunlight exposure, which causes vitamin D to be made in the skin, and any dietary intake from food provide only about 125ìg per day and 10 ìg per day maximum, respectively. The researchers felt that further studies that included a diverse, large population and used a dose dependent vitamin D supplementation vs. 25-hydroxyvitamin D and calcium blood concentration protocol could raise this upper limit even higher.
It should be noted that the researchers concluded that other possible side effects of vitamin D supplementation, i.e. kidney stones and cardiovascular disease, were not a problem at this level.
Source: Hathcock, John N., et al. “Risk assessment for vitamin D.” The American journal of clinical nutrition 85.1 (2007): 6-18.
© 2007 American Society for Nutrition
Posted August 5, 2008.
References:
- Giovannucci E, Liu Y, Rimm EB, et al. Prospective study of predictors of vitamin D status and cancer incidence and mortality in men. J Natl Cancer Inst 2006;98:451–9.
- Liu S, Song Y, Ford ES, Manson JE, Buring JE, Ridker PM. Dietary calcium, vitamin D, and the prevalence of metabolic syndrome in middle-aged and older U.S. women. Diabetes Care 2005;28:2926 –32.
- Holick MF. High prevalence of vitaminD inadequacy and implications for health. Mayo Clin Proc 2006;81:353–73.
