Bone FractureElderlyVitamin D

Negative response to a single very high dose of vitamin D

Lots of research points to the need to increase our intake of cholecalciferol (vitamin D).

Here’s a study by researchers at the University of Melbourne, in Australia that cautions against giving too much at once.

First, the details.

  • 2256 community-dwelling elderly women at high risk of fracture were randomly assigned to a treatment group each autumn to winter for 3 to 5 years.
    • Cholecalciferol 500,000 IU
    • Placebo
  • Falls and fractures were recorded using monthly calendars and confirmed by telephone interview.
  • Fractures were radiologically confirmed.
  • 137 of these women were randomly selected to give blood samples for 25-hydroxycholecalciferol and parathyroid hormone levels.
  • Neither the patients nor researchers knew the treatment given — double blind.

And, the results.

  • Women in the vitamin D group were significantly more likely to fall and fracture their bones.
    • 83 vs 73 falls per 100 person-years with placebo
    • 171 vs 135 fractures with placebo
  • The relative risk for fracture was significantly greater in the vitamin D group.
    • 5 vs 4 fractures with placebo per 100 person-years
  • There was a significantly greater risk of falling earlier in the study vs later.
  • In the vitamin D group, vitamin D blood levels increased at 1 month after dosing to approximately 120 nmol/L, were approximately 90 nmol/L at 3 months, and remained higher than the placebo group 12 months after dosing.

The bottom line?

In an elderly group of people at risk of falling, a single high dose of vitamin D was associated with a greater risk of falling and fracture compared to placebo.

The authors concluded, “This is the largest total annual dose of vitamin D (500,000 IU) reported in any large randomized controlled trial, raising the possibility that the adverse outcome is dose-related.”

However, the authors also tell us that a flaw in the study design might have contributed to the findings. Specifically, the presence of existing vertebral fractures might have been higher than estimated at the start of the study, because participants were not evaluated at the study center, and there was no biochemical assessment of all participants.

5/13/10 16:07 JR

Hi, I’m JR

John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at, a complementary and alternative medicine website.