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High-dose vitamin D taken once a year may increase falls and fractures in older women

May 11, 2010

By Patricia Nicholson

A study designed to test whether a single, annual high dose of vitamin D could reduce fractures and falls in older women found that this approach in fact increased falls and fractures.

After an average of 3.5 years in the study, women taking the high-dose annual vitamin D treatment had a 15 per cent higher fall rate and 26 per cent higher fracture rate compared to women who weren’t taking the supplement.

Studies on the effectiveness of vitamin D in preventing fractures have had inconsistent results in the past.

In this double-blind trial, Australian researchers randomly assigned 2,256 women over age 70 to receive either a single annual dose of 500,000 IU of vitamin D, taken orally, or a placebo for a period of three to five years. None of the women lived in a nursing home or assisted-living facility, and all were considered at high risk for fractures.

There were 171 fractures in the vitamin D group, compared to 135 in the placebo group. The vitamin D group experienced 2,892 falls, compared to 2,512 in the placebo group.

The researchers noted that women in the vitamin D group had significantly more falls during the first three months after their annual vitamin D dose, compared to the remaining nine months of the year.

The study used one of the largest reported annual doses of vitamin D studied, so the increased fall and fracture rates may be related to high dose. The researchers noted that other studies using a similar total amount of vitamin D, but administered by injection in four doses per year, did not find that vitamin D increased falls and fractures. This, as well as the increase in falls and fractures the researchers observed in the first three months after taking the single dose, supports the theory that increased fall and fracture risk may be related to the large single dose.

The study results underscore the need for further understanding of how dosage of vitamin D may affect its usefulness in fracture prevention. The study appears in the May 18, 2010 issue of JAMA.

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