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High dose of vitamin D may increase fracture risk in older women
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A single, annual high dose of vitamin D resulted in a higher rate of falls and fractures for women older than 70 years compared with those taking placebo, according to the results of a level 1 trial.
The study, conducted by Kerrie M. Sanders, PhD, of the University of Melbourne, Geelong, Australia and colleagues, was published in the Journal of the American Medical Association.
“This is the first study to demonstrate increased risk of falls associated with any vitamin D intervention, and the second study to demonstrate an increased fracture risk associated with annual high-dose vitamin D therapy in elderly women,” the researchers wrote, noting that the total annual dose of cholecalciferol 500,000 IU administered in their study was the largest of any single dose reported in the literature, which may have contributed to the adverse outcome.
Study design
The placebo-controlled, double blind trial included 2,256 community-dwelling women older than 70 years who were considered to be at high risk for fracture. The participants were randomly assigned to receive either a single dose of cholecalciferol 500,000 IU or placebo each year for three to five years. Cholecalciferol was administered annually to 1,131 study participants, while 1,125 received a placebo.
A total of 5,404 falls occurred among the trial participants during the study period, with 74% of 837 women in the vitamin D group and 68% of 769 women in the placebo group having at least one fall, according to a JAMA press release. Women in the annual high-dose vitamin D group experienced 15% more falls. Women in the vitamin D group had 171 fractures vs. 135 in the placebo group. In comparison with the placebo group, the vitamin D group had 26% more fractures and a 31% higher incidence of falls in the first three months following dosing.
Possible explanations
In addition to the large dose, the researchers suggested that the dosing regimen may have also played a role in the outcome. They cited two other studies that used the same annual dose, administered intramuscularly every 4 months, in which vitamin D was not associated with increased risk of falling or fracture.
“Thus, it is reasonable to speculate that high serum levels of vitamin D or metabolites resulting from the large annual dose, subsequent decrease in the levels, or both might be causal,” the researchers wrote, and called for further investigation into the safety of high doses of vitamin D.
Sanders KM. JAMA. 2010;303:1815-1822.