Older people taking a class of drugs for anxiety or sleep issues may be facing increased risks of eventually developing Alzheimer's disease, research suggests.

Benzodiazepine drugs -- marketed under names such as Valium, Xanax, Klonopin and Ativan -- are widely prescribed as a treatment for insomnia, anxiety and agitation, all considered early warning signs of possible Alzheimer's in elderly patients.

Although widely used in treating such symptoms thought to be early signs of dementia onset, a study by French and Canadian researchers has raised the possibility the drugs may in fact allow, cause or accelerate the onset of the dementia involved in Alzheimer's.

The study, involving elderly Canadian adults, revealed that those in the study who had taken benzodiazepine for 3 months or more at some point in the past showed an increase in the risk, up as much as 51 percent, of developing dementia.

Most medical guidelines suggest benzodiazepine class drugs should be administered for no more than 8 to 12 weeks.

While a link between the drugs and dementia is not definitive, the study is a strong indication such drug treatments should last more than 3 months, the researchers wrote in the journal BMJ.

"Benzodiazepine use is associated with an increased risk of Alzheimer's disease," lead researcher Sophie Billioti de Gage of the University of Bordeaux, France, and colleagues said.

"Unwarranted long-term use of these drugs should be considered as a public health concern," they said.

The study looked at 2,000 cases of Alzheimer's in adults in Quebec age 66 and older, all of whom had been given benzodiazepines.

That population was compared with a control group of 7,000 healthy Quebec residents in the same age bracket who had taken none of the drugs.

The researchers found that at the end of a 5-year period after an initial use of benzodiazepines, there was a steadily mounting of risk of Alzheimer's.

Although an increased risk was clearly associated with the drugs, the exact nature of the link is unclear at this time, the researchers acknowledged.

Still, there has been previous research showing regular or frequent use of benzodiazepines can degrade memory and lower mental performance.

Other studies have yielded evidence that regular intake of the drugs can cause reduced activity in the receptors they bind to.

A decrease in such receptor activity has previously been linked to a decline in cognitive performance.

"In view of the evidence, it is now crucial to encourage physicians to carefully balance the risks and benefits when initiating or renewing a treatment with benzodiazepines and related products in older patients," the researchers wrote.