Who would have thought that popping a pill could help prevent falls in the elderly? According to a new report on fall prevention, published in Annals of Internal Medicine, vitamin D, of all things, may help adults age 65 and older stay steady and upright.

Falls are the leading cause of injury in adults 65 and older, and preventing them is much more effective than treating them. Thirty percent to 40 percent of the elderly fall at least once a year; many who had been living independently never regain their previous functioning, ending up in assisted living and nursing homes.

Taking vitamin D supplements daily is one of three major recommendations on fall prevention recently issued by the United States Preventive Services Task Force. "The exact mechanism is not known, but it seems to help muscle strength and balance," said Dr. Al Siu, vice chairman of the task force and chairman of the geriatrics and palliative medicine department at Mount Sinai School of Medicine.

And the help is significant. In a review of nine trials, the task force found that a daily dose of 800 international units (I.U.) reduced the risk of falling by about 17 percent, compared with those who did not take the vitamin.

The task force is the first major medical group to recommend vitamin D supplements for those who live at home (not in assisted living or nursing homes) and are at higher-than-normal risk of falling - that is, those over age 65 who have already fallen or who have had limitations in mobility within the last year.

That may come as a surprise, since in another recent draft report the task force also recommended against postmenopausal women taking vitamin D to prevent fractures.

According to Dr. Siu, the fractures report looked at a larger population: all men and women, not just those at high risk for falling. Second, it made negative recommendations only for lower doses of vitamin D - less than 400 I.U. daily.

"We do have evidence that low doses of vitamin D and calcium supplementation for postmenopausal women do not work," Dr. Siu said. "We don't know if higher doses work - the evidence is insufficient. So for the larger population of older men and women, we don't say 'Take it' or 'Don't take it.' "

But for those at increased risk of falling, Dr. Siu added, the task force decided that there was sufficient evidence that 800 I.U. of vitamin D taken daily can help prevent further tumbles.

Not all experts are so enthusiastic. The American Geriatrics Society and the British Geriatrics Society, in updated fall prevention guidelines issued last year, merely recommended that vitamin D supplements be "considered."

Those guidelines focused more on advising doctors to review medications used by patients that might increase falls. In another new recommendation on fall prevention, the preventive services panel took a different tack, saying that doctors should do a "multifactorial risk assessment with comprehensive management of identified risks."

Translation: Doctors should be asking their patients more questions than they typically do about a history of falls - and should observe their patients in action - to identify those at higher-than-average risk.

"It isn't standard practice for doctors to ask if you've fallen in the last 6 to 12 months or to observe patients walking and see if they can get up and walk at a normal pace or not," said Dr. Siu - but it should be.

The task force's last recommendation for fall prevention involves exercise. Though the new report is short on specifics (unlike those by the American and British geriatrics societies, which commend tai chi), Dr. Siu said the appropriate exercise should be any balance, strengthening and aerobic moves the patient likes enough to actually do regularly.

The physical therapy should be customized to correct uneven gaits and to keep patients mobile, helping them maintain or regain strength. "No one size fits all," said Dr. Siu.

So is that all the elderly and their caregivers need to know about preventing falls? Probably not. The task force reviews medical research to make unbiased recommendations about what works best to prevent illness and injury. The guidelines are based on whether the benefits of an intervention outweigh the harms, without considering the cost involved.

The task force did not address hazards around the house, which are implicated in more than one-third of falls among the elderly, according to Jon Pynoos, a gerontologist at the University of Southern California and a director of the Fall Prevention Center of Excellence in Los Angeles.

"Most people live in 'Peter Pan' housing, not designed for anyone who will grow up or grow old, so the home is an accident waiting to happen for older people," said Dr. Pynoos.

If you cannot wait for an occupational therapist to do an evaluation of your home, here are the prime places to start on your own.

Unsurprisingly, stairs are the most likely places to experience serious falls. Put up railings on both sides. Replace worn carpet, as it can be slippery. Install lighting at the top and bottom of the stairs. Mark the top and bottom steps clearly with a different color of carpeting (tape tends to need replacing too often). Stair glides are excellent, but expensive.

Bathrooms are the next big fall zone. Hard tiled surfaces are slippery when wet and unforgiving on fragile aging bones. Secure grab bars (not the suction-cup variety) into the walls at varying easy-to-grab angles in addition to vertically and horizontally. Place them not only where you enter the tub or shower but also in a second midway spot - for example, where the built-in soap holder usually is, and by the toilet.

A more costly solution: "I recommend walk-in showers - they have no lip," said Dr. Pynoos. Costs start at $1,000.

"Comfort-height" toilets, slightly higher than regular ones, can make getting down and up easier, with less chance of losing balance. Nonskid tiles are wise.

Good lighting throughout the home can be an easy and inexpensive safety improvement. Dr. Pynoos recommends extensive deployment of night lights with light and motion sensors.

Getting rid of clutter is critical but, as readers here know, easier said than done. "Some older people are hoarders - for me, it's books," Dr. Pynoos said. The key is to get the stuff - newspapers, magazines, books, whatever - off the floor.

Pets and their paraphernalia can also pose a hazard. Pet collars that glow at night or have bells can help reduce the chances that an elderly owner will trip over Fido. Still, it'll take a genius to figure out how to stash the water bowl both near the sink and completely out from underfoot. (If you've figured out a fix, let us know.)

"I did some of these things for my father-in-law's house," recalled Dr. Pynoos, "and he said to me: 'This is the best gift you could have given me - redesigning things so I can live independently.' "

This post has been revised to reflect the following correction:

Correction: July 13, 2012

An earlier version of this article misstated, in a quotation, the family member whom Jon Pynoos said he helped by taking measures to prevent falls in the home. Dr. Pynoos did this for his father-in-law, not his father.