The risk is there even after taking into account things such as weight, age and the use of sleep medications, said Katie Stone and colleagues at the California Pacific Medical Center Research Institute in San Francisco.

"Sleep deprivation in younger adults leads to slower reaction times, and this may represent an unmeasured factor that could explain these findings," they wrote in a report published in the Archives of Internal Medicine.

The study involved nearly 3,000 women 70 and older who were followed for a number of years.

Women in the study who slept no more than five hours per night had a 50 percent higher risk of having two or more falls over the course of a year than those who slept more than seven hours, the researchers found.

For those who slept from five to seven hours, the risk was 40 percent higher than for the longest sleepers.

Stone said in an interview that while the study involved only women, preliminary results from research she is now doing indicate that the same can be said for elderly men.

"It's definitely a problem in both men and women," she said.

People who have trouble sleeping are often given benzodiazepines – anti-anxiety drugs that can help insomnia – but previous research had not determined whether it was poor sleep or the medications used to treat it that caused falls, the researchers said.

The use of those drugs and the increased risk of falls "may be in part explained by poor sleep," the researchers said.

The team said more comprehensive studies are needed to look at the relationship of falls to such things as sleep-fragmenting breathing disorders and the use of newer sleep drugs.