People over the age of 65 who take certain sleeping pills or anti-anxiety medications may face a higher risk of developing dementia within 15 years compared with those who never took the pills, a study suggests.

Benzodiazepines are used to treat anxiety and insomnia. It’s estimated that between 22 per cent and 27 per cent of Canadians over the age of 65 use the drugs regularly, a rate that rises to more than 30 per cent among those over age 85, according to a 2010 study in the Canadian Pharmacists Journal.

Benzodiazepines are meant to be taken for up to six weeks to treat insomnia. (Reuters)

Benzodiazepines are meant to be taken for up to six weeks to treat insomnia and Health Canada recommends taking them for anxiety for no more than two months.

But in Thursday's online issue of the British Medical Journal, researchers from France found 1.55 times higher odds of dementia among benzodiazepine users than non-users living in southwest France over 15 years of followup.

Chronic use raises public health concern

"In this large, prospective, population based study of people who were free of dementia and did not use benzodiazepines until at least the third year of followup, new use of benzodiazepines was associated with a significant, approximately 50 per cent increase, in the risk of dementia," Bernard Bégaud of the University of Bordeaux and his co-authors concluded.

"Our data add to the accumulating evidence that use of benzodiazepines is associated with increased risk of dementia, which, given the high and often chronic consumption of these drugs in many countries, would constitute a substantial public health concern."

Researchers said they started looking for dementia after three years to adjust for factors associated with starting to use benzodiazepines. Insomnia, depression and anxiety are the main indications for prescribing benzodiazepines. Since the same symptoms can also occur early in dementia, it can be difficult for investigators to sort out cause and effect.

They noted that benzodiazepines remain useful for treating acute anxiety and insomnia.

Drawbacks of the study included a limited number of new users of the drugs when the study began, and an inability to adjust for anxiety and sleep disorders separately.

The benzodiazepines included in the study were alprazolam, bromazepam, chlordiazepoxide, clobazam, clonazepam, clorazepate, clotiazepam, diazepam, estazolam, flunitrazepam, loflazepate, loprazolam, lormetazepam, nitrazepam, nordazepam, prazepam, oxazepam, temazepam, tetrazepam, tofizopam, triazolam, zolpidem, and zopiclone.

The study was funded by academic research grants.