Opposing previous research, the new study found no link between benzodiazepine use and increased risk of dementia.
Study coauthor Shelly Gray, of the School of Pharmacy at the University of Washington, and colleagues publish their findings in The BMJ.
Benzodiazepines are a class of drugs that increase the level of the neurotransmitter gamma-aminobutyric acid (GABA) in the brain, producing sedative, anti-convulsant, anti-anxiety, hypnotic and muscle relaxant effects.
Benzodiazepines are most commonly used to treat anxiety and insomnia, though they are used for a number of other conditions, including alcohol withdrawal, panic disorders and seizures. Common types of benzodiazepines include diazepam, alprazolam and flurazepam.
In the US, benzodiazepine use is highest among older individuals; a 2014 study from the National Institutes of Health (NIH) found that around 8.7% of adults aged 65-80 received a benzodiazepine prescription in 2008, compared with 2.6% of those aged 18-35.
Numerous studies, however, have associated benzodiazepine use in seniors with increased risk of dementia. A 2012 study reported by Medical News Today, for example, suggested adults aged 65 and older are 50% more likely to develop dementia within 15 years of using benzodiazepines, while a more recent study suggested benzodiazepine use for at least 3 months increases older adults' risk of Alzheimer's disease by 51%.
However, Gray and colleagues note that research assessing benzodiazepine use in older adults has been conflicting, with some studies finding no link with dementia.
"Given the enormous public health implications, we need a better understanding of the potential cognitive risks of cumulative benzodiazepine use," say the authors.
No dementia link, but seniors should still avoid benzodiazepines
With this in mind, the team set out to determine whether higher cumulative use of benzodiazepines among older adults is associated with increased risk of dementia or faster cognitive decline.
To do so, the researchers analyzed the data of 3,434 adults aged 65 and older who were part of the Adult Changes in Thought study, conducted within Group Health - a non-profit health care system in Seattle, WA.
All participants were free of dementia at study baseline, and cognitive screening was conducted at enrollment and every 2 years thereafter. Subjects were followed-up for an average of 7 years.
Pharmacy data from Group Health was analyzed to assess participants' daily use of benzodiazepines over a 10-year period.
During follow-up, 797 of the participants developed dementia. Of these, 637 developed Alzheimer's disease. The median level of benzodiazepine use among participants was the equivalent to 1 year of daily use.
The researchers found that subjects with the highest benzodiazepine use were at no higher risk for dementia or Alzheimer's than those with lower benzodiazepine use, nor did they experience faster cognitive decline.
While the researchers did identify a small increased risk of dementia among participants with low or moderate benzodiazepine use - the equivalent of up to 1 month of use or 1-4 months use, respectively - they suggest this may "represent treatment of prodromal symptoms" of dementia.
"It is also possible that people with prodromal dementia, even years before diagnosis, could be more sensitive to benzodiazepine induced acute cognitive adverse events (for example, delirium), resulting in discontinuation of the drug and avoidance, in turn leading to low levels of use," they add.
Commenting on their findings, the researchers say:
"Overall, our pattern of findings does not support the theory that cumulative benzodiazepine use at the levels observed in our population is causally related to an increased risk for dementia or cognitive decline."
Still, the team says that considering the other adverse effects associated with benzodiazepine use and the fact that evidence remains mixed as to whether the drugs may raise the risk for dementia, health care providers "are still advised to avoid benzodiazepines in older adults to prevent important adverse health outcomes, withdrawal and dependence."
In June 2015, MNT reported on a study linking increased risk of homicide with benzodiazepine use.