Contrary to earlier findings, taking common painkillers such as ibuprofen and naproxen may not prevent Alzheimer's disease, but may delay it, U.S. researchers said on Wednesday.

Earlier studies had suggested that drugs known as non-steroidal anti-inflammatories or NSAIDS, which also include aspirin, could protect people from dementia.

But a large study with older patients done by researchers at the University of Washington and the U.S. Department of Veterans Affairs in Seattle found the dementia risk was actually higher among heavy NSAID users.

The findings contradict the results of several studies that found drugs like ibuprofen — sold under many brand names, including Motrin and Advil — and naproxen, sold as Aleve, can prevent Alzheimer's disease.

Researchers are struggling to find ways to protect against Alzheimer's, a mind-robbing disease with no cure and few effective treatments.

Alzheimer's disease has been linked with inflammation, and researchers have assumed that anti-inflammatory drugs might help delay onset of the disease.

Dr. John Breitner and colleagues studied 2,736 members of a large health system who had an average age of 75 and no signs of dementia when they started.

Of the participants, 351 people had a history of heavy use of NSAIDs at the start of the study, and another 107 people became heavy NSAID users during the 12-year follow-up period.

During the study, 476 people developed Alzheimer's disease or dementia. The risk of developing dementia among heavy NSAID users was 66 percent higher than among people with little or no NSAID use.

Breitner and colleagues think age may help explain differences between their findings and other studies showing a prevention benefit.

"The results observed elsewhere may reflect delayed onset of Alzheimer dementia in non-steroidal anti-inflammatory drug users," they wrote in the journal Neurology.

"Conceivably, such delay could result in increased incidence of Alzheimer disease incidence in late old age."

Dr. David Bennett of Rush University Medical Center in Chicago and Rachel Whitmer, a research scientist at Kaiser Permanente in Oakland, California, said in a commentary that researchers will study younger patients over a longer period of time to understand whether the drugs prevent or delay Alzheimer's disease.

"Although dementia becomes clinically apparent in old age, it is a disease of a lifetime," they wrote, adding that neurologists will have to wait for an answer.

An estimated 26 million people have Alzheimer's disease, which is the most common form of dementia. The disease starts out with mild memory loss and confusion, but escalates into complete memory loss and an inability to care for oneself.