A Single Annual High Dose of Vitamin D Is the Reverse of Helpful

Sometimes a good idea in medical treatment can go very wrong.  This is bad news for a profession whose precept is “first, do no harm” (primum non nocere).  An example of this sort of result is reported by Australian researchers in the Journal of the American Medical Association.

Globally, there is widespread insufficiency and deficiency of vitamin D.  Older women, in particular, are likely to risk associated osteoporosis, leading to falls and fractures.  University of Melbourne researchers wanted to improve vitamin D status in older women, and studied whether a once-a-year dose of 500,000 International Units could be used effectively to overcome the problem of poor adherence to daily supplementation.  They did a double-blind, placebo-controlled trial of 2256 women aged 70+, who were randomly assigned to take cholecalciferol or placebo each fall to winter for 3 to 5 years.  Falls and fractures were ascertained by monthly calendars and/or phone calls.  A subset of 137 participants had serial blood sampling for 25-hydroxycholecalciferol and parathyroid hormone levels.

There were 171 fractures in the vitamin D group, vs. 135 in the placebo group.  And 837 women in the vitamin D group fell 2,892 times, while 769 women in the placebo group fell 2,512 times.  Overall, fractures were 1.26 times more frequent in the vitamin D group.  But this ‘relative risk’ in the vitamin D group was higher during the first 3 months after dosing; it was 1.31 in these months, and then 1.13 in the next 9 months.  The subset group blood analyses showed that the 25-hydroxycolecalciferol remained higher in the vitamin D than in the placebo group throughout the study – about 40% higher, on average.

This unexpected negative result has led to some head scratching.  One expert suggested that the women getting the supplement felt better in the first 3 months after treatment and were therefore more physically active, and thus exposed to a greater risk of falling.  At all events, the use of a single annual 500,000 dose seems to be unsuitable.  This doesn’t mean one should back off from treating vitamin D deficiency and insufficiency.  The latest recommendation from the International Osteoporosis Foundation is that the average requirement is 800 to 1,000 IU daily, increasing to 2,000 IU daily for individuals who are obese, have osteoporosis, limited sun exposure, or poor absorption from the intestines.