People who take a group of drugs commonly used to treat anxiety and insomnia may have an increased risk of developing Alzheimer's disease, a study has found.

Benzodiazepines, also known as sedatives or tranquillisers, are a group of medications that help to regulate sleep, ease agitation and reduce anxiety. They include diazepam (Valium).

Dementia currently affects around 36 million people worldwide, including some 40,000 people in Ireland. Alzheimer's disease is the most common type of dementia, accounting for up to 80% of all cases.

While a link between dementia and users of benzodiazepines has been found, the nature of this link has remained unclear, so researchers in France and Canada decided to investigate further.

They looked at the development of Alzheimer's disease in a group of older people who had been prescribed benzodiazepines. Over a six-year period, almost 1,800 cases of Alzheimer's were detected and these were compared to over 7,000 people of similar age who did not have the disease.

The study found that those who had in the past used benzodiazepines for three months or more had an increased risk - up to 51% - of developing Alzheimer's disease. This link became stronger the longer they used the drugs.

The researchers noted that while the nature of the link is still not clearly understood, the strong association seen with longer exposure to these drugs ‘reinforces the suspicion of a possible direct association, even if benzodiazepine use might also be an early marker of a condition associated with an increased risk of dementia'.

They emphasised that these drugs are ‘indisputably valuable' when it comes to the treatment of anxiety and insomnia, but they warned that use of them ‘should be of short duration and not exceed three months'.

"The findings are of major importance for public health, especially considering the prevalence and chronicity of benzodiazepine use in elderly populations and the high and increasing incidence of dementia in developed countries. It is now crucial to encourage physicians to carefully balance the benefits and risks when initiating or renewing a treatment with benzodiazepines in elderly patients," the researchers concluded.

Details of these findings are published in the British Medical Journal.

For more information on Alzheimer's disease, see our Alzheimer's Clinic here