CHICAGO, May 12 (Reuters) - Giving elderly people either Aleve or Celebrex, two anti-inflammatory painkilling drugs, did nothing to ward off the mental decline associated with the onset of Alzheimer's disease, researchers said on Monday.

Several studies have suggested that long-term use of certain painkillers in the class known as non-steroidal anti-inflammatory drugs, or NSAIDs, can lower the risk of developing the memory-wasting disease.

However, using NSAIDs for long periods can pose health risks such as stomach bleeding and kidney problems.

Barbara Martin of Johns Hopkins University in Baltimore and colleagues concluded there was no protective effect from the two commonly used drugs. They added that Aleve, known generically as naproxen, may have had a slightly negative impact.

Patients who took two daily doses of Aleve scored slightly lower on tests of mental functioning compared to the groups taking a placebo or celecoxib.

The nearly four-year study, published in the Archives of Neurology, divided 2,117 people aged 70 or older with a family history of Alzheimer's into three groups.

One group received naproxen twice daily in the form of Bayer's <BAYG.DE> Aleve, another Pfizer Inc's <PFE.N> Celebrex, known generically as celecoxib, and a third group took a placebo.

Each participant had a close relative with Alzheimer's, a known risk factor for the disease that has no cure and few effective treatments.

The researchers suggested that certain NSAIDs may protect against dementia only when given several years before mental functioning begins to decline.

Some doctors believe persistent inflammation may play a role in mental decline and Alzheimer's, a disease that affects more than 5 million Americans and is the most common form of dementia.

Another study by a different team and published last week in the journal Neurology concluded that taking ibuprofen, commonly sold as Advil or Motrin, for at least five years cut the risk of developing Alzheimer's by 40 percent.

Some other NSAIDs reduced the risk of developing the illness by 25 percent, though Celebrex did not, the team at Boston University School of Medicine said.

Celebrex is one of a class of painkillers that selectively block the COX-2 enzyme, which is linked to inflammation. Other NSAIDS such as aspirin and naproxen affect both COX-1 and COX-2, and the COX-2 drugs were designed to be more specific and thus safer.

Merck & Co. Inc <MRK.N> pulled its COX-2 inhibitor, Vioxx, from the market in 2004 after studies showed it raised the risk of heart attacks and strokes in long-term users. Pfizer withdrew a similar drug, Bextra, but has continued to market Celebrex.

The latest study was ended early because of the heart attack and stroke concerns about this class of drugs. (Reporting by Andrew Stern; Editing by Maggie Fox)

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