Taking vitamin D supplements, at a dose of 700-1,000 international units per day, may make falling 19% less likely for people aged 65 and older.

That news comes from a research review published online in BMJ, formerly called the British Medical Journal.

The review is based on eight studies of people aged 65 and older who took vitamin D supplements or placebos. Doses of vitamin D differed among the studies. Participants lived in nursing homes or in their own homes.

The reduction in fall risk was only seen in people who took at least 700 international units (IU) per day of vitamin D. Taking smaller doses didn't appear to help.

The reviewers -- who included Heike Bischoff-Ferrari, MD, MPH, director of the Centre on Aging and Mobility at Switzerland's University Hospital Zurich -- also noticed that the reduction in fall risk was only seen in people who achieved a vitamin D blood level of at least 60 nanomoles per liter.

Vitamin D affects muscle strength, and stronger muscles could mean less likelihood of falling, note Bischoff-Ferrari and colleagues.

The reviewers aren't ruling out the possibility that higher doses of vitamin D supplementation might be even more effective at preventing falls. But the studies they reviewed didn't include doses higher than 1,000 IU per day.

Taking too much vitamin D can cause nausea, constipation, confusion, abnormal heart rhythm, and kidney stones.

In the U.S., the Institute of Medicine (IOM) considers 200 IU of vitamin D to be an "adequate" daily intake for people up to 50 years old, an intake of 400 IU for people aged 51-70, and an intake of 600 IU for people aged 71 and older. The IOM also considers the tolerable upper limit for vitamin D intake to be 2,000 IU per day (1,000 IU per day in the first year of life).

However, many experts argue that the adequate daily intake for vitamin D should be higher. The IOM is reviewing its vitamin D recommendations and is expected to announce the results of that review next year.