LONDON (AP) - A new study raises the possibility that people who drink a lot of coffee might be more likely to develop the debilitating immune system disease rheumatoid arthritis.

The Finnish study, published this week in the British Medical Association journal Annals of the Rheumatic Diseases, found that people who drank more than four cups a day had twice the chance of getting the disease as those who drank fewer.

While the study does not prove drinking coffee causes rheumatoid arthritis, it is the first to produce evidence of a possible link. Some experts said it was worth investigating further, while others questioned whether the findings could be true.

Scientists do not know what causes rheumatoid arthritis - which afflicts about 1 percent of people and is incurable - but recent studies have raised suspicions about smoking and obesity.

This is not the type of arthritis common in the elderly because of the wear-and-tear of aging. Rheumatoid arthritis occurs when the immune system goes awry and attacks the joints, causing severe inflammation, pain and stiffness.

The new study followed the coffee drinking habits of 19,000 Finnish people over 15 years. None had rheumatoid arthritis when the study began in the 1970s.

By 1989, 0.5 percent of those who drank more than three cups of coffee developed rheumatoid arthritis. About 0.2 percent of the people who drank three cups of coffee a day or less got the disease.

The study hypothesized that some unidentified ingredient in coffee may trigger the production of rheumatoid factor, an antibody that can be detected in the blood years before the onset of arthritis.

Because the Finns are heavy coffee drinkers, there weren't enough non-drinkers to make a comparison that might show how important a role coffee drinking might be, said one of the study's authors, Dr. Kimmo Aho, a professor of immunology at the National Public Health Institute in Helsinki.

But Dr. David Isenberg, director of the Center for Rheumatology at University College, London University, said he was skeptical of the study's conclusions.

"If Finland has a high rate of coffee drinking, why doesn't it have a higher prevalence of rheumatoid arthritis than other countries?" he said.

About 1 percent of Finns get the disease - a similar rate to other nationalities.

Isenberg also said he was suspicious of the findings because the study did not adjust the results well enough to eliminate the influence of other factors that may have played a role in the development of the disease

"There's a chance that you will find something that randomly correlates - which means it might be a fluke," he said.

Dr. Paul Bacon, professor of rheumatology at the University of Birmingham in England, said the findings were worthy of further study.

"You want to know what's going on in other countries to see if there really is an effect or if there is something else at work related both to coffee drinking and rheumatoid arthritis, or if it has something to do with the way they drink coffee in Finland," he said.

Aho said it was impossible to tell whether one type of coffee could be worse than another, but that the effect might be linked to the way the Finns prepared the coffee.

He noted that boiled coffee was popular in Scandinavia until filtered coffee became dominant in the 1980s. Instant coffee is not drunk by many people there, he said.

Boiled coffee, which is left on a warm stove all day, dissolves many of the substances in ground coffee that don't make it through paper filters, and gets more concentrated as the day wears on.

Aho said he believed that if the effect is real, much of it might be because the coffee was boiled. He said he suspected espresso coffee may produce a similar effect because it also is concentrated.

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