Kim Painter

Special for USA TODAY

Medications widely used for anxiety and insomnia are linked to an increased risk of Alzheimer's in a new study.

The study, published Tuesday in the medical journal BMJ, does not prove a cause-and-effect relationship between benzodiazepines – drugs such as Xanax, Ativan and Valium – and dementia. But it does show Alzheimer's was 51% more common in older adults who took the drugs in the past.

The risk started to show up with three months of use and rose from there. It was greatest in patients who took long-acting versions.

"It is not surprising that benzodiazepines are associated with adverse cognitive effects," says an editorial written by Kristine Yaffe of the University of California, San Francisco, and Malaz Boustani of the Indiana University Center for Aging Research.

The question, those experts say, is whether the effects, including diminished memory and thinking skills, are passing or potentially permanent. The new study is rigorous enough to raise concerns about irreversible effects in long-term users, they say.

For the study, researchers in Canada and France reviewed health records of 1,796 people diagnosed with Alzheimer's and 7,184 other adults over age 66, all from Quebec. The link with benzodiazepines was found in health records going back at least six years before the diagnoses.

One obvious reason for a link could be that people who go on to develop Alzheimer's first develop anxiety, depression and trouble sleeping – which they treat with pills. The researchers say they adjusted their results to account for earlier diagnoses of those conditions and still found what appears to be an independent link with Alzheimer's, but they said they cannot be sure that all previous health problems showed up in the records. They also cannot be sure that patients took all the pills they were prescribed.

The American Geriatrics Society already cautions doctors against routinely prescribing benzodiazepines to older adults. Studies link the drugs with car crashes, falls and hip fractures, the group says.

Despite such warnings, the medications are used by nearly half of older adults, the study's authors say.