As the most common form of dementia, Alzheimer's disease affects almost 500,000 people in the UK.
Although the cause is currently unknown, there are many factors believed to increase the risk of developing the condition.
Most recently, popular sedative Benzodiazepines, which are widely prescribed to treat anxiety and insomnia, have been associated with a heightened risk of developing the condition, particularly for long-term users.
Researchers cautioned that unwarranted long-term use of the drugs should be considered a public health concern.
The study, published on thebmj.com, examined data from a health insurance database in Quebec.
French and Canadian researchers identified 1,700 elderly people with Alzheimer's disease and more than 7,000 healthy people for comparison.
They found that past use of benzodiazepines for three months or more was associated with an increased risk of developing Alzheimer's. The risk varied between 43% and 51%, they found.
The strength of association increased with the longer exposure, they found. It also increased if people used long-acting benzodiazepines rather than short-acting ones.
"Our study reinforces the suspicion of an increased risk of Alzheimer-type dementia among benzodiazepine users, particularly long-term users, and provides arguments for carefully evaluating the indications for use of this drug class," the authors wrote.
"Our findings are of major importance for public health, especially considering the prevalence and chronicity of benzodiazepine use in older people and the high and increasing incidence of dementia in developed countries."
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Commenting on the study, Dr Liz Coulthard, consultant senior lecturer in dementia neurology, University of Bristol, said: "This work provides yet another reason to avoid prescription of benzodiazepines for anything other than very short-term relief of insomnia or anxiety.
"In addition to short-term cognitive impairment, falls and car accidents already known to be associated with benzodiazepine use, there is a hint from this study that these drugs might in some way increase the risk of developing Alzheimer's disease."
Dr Eric Karran, director of research at the charity Alzheimer's Research UK, added: "This study shows an apparent link between the use of benzodiazepines and Alzheimer's disease, although it's hard to know the underlying reason behind the link.
"One limitation of this study is that benzodiazepines treat symptoms such as anxiety and sleep disturbance, which may also be early indicators of Alzheimer's disease.
"We know that the processes that lead to Alzheimer's could start more than a decade before any symptoms show.
"This study looks at benzodiazepine use five to 10 years before diagnosis, and so the disease is likely to have already been present in some people.
"Benzodiazepines have been shown to cause memory problems as part of their side effects and so it is difficult to tease out cause and effect in studies such as this.
"We need more long-term research to understand this proposed link and what the underlying reasons behind it may be."Suggest a correction