The caffeine found in less than two cups of coffee a day might be enough to dull the effects of the drug methotrexate in people with rheumatoid arthritis, a small study suggests.
Israeli researchers found that among 39 adults with rheumatoid arthritis, those with the highest caffeine intake--comparable to about one-and-a-half cups of coffee or more per day--showed a weaker response to methotrexate than did patients with the lowest caffeine intake.
According to the researchers, caffeine may interfere with methotrexate's ability to fight rheumatoid arthritis because caffeine acts on cell receptors called adenosine receptors. It's not yet clear why methotrexate helps rheumatoid arthritis, but one theory is that it increases adenosine production, which in turn reduces the inflammation that marks rheumatoid arthritis.
The investigators call for larger studies to look at the possible interaction between methotrexate and caffeine in people with rheumatoid arthritis. They have said that rheumatoid arthritis patients on methotrexate "might want to consider" easing up on caffeine.
Earlier research in animals had suggested a caffeine-methotrexate connection, and this latest study has "taken the next step" by finding a relationship in people with rheumatoid arthritis.
All of the study participants were recently diagnosed with rheumatoid arthritis and were started on 7.5 milligrams (mg) of methotrexate a week. Their symptoms and daily diets were followed for three months, and patients were analyzed in three groups based on their caffeine intake.
By the end of the study, participants with the highest caffeine consumption showed less improvement in morning stiffness and joint pain compared with the lowest-intake group.
According to the researchers, a daily intake of more than 180 mg of caffeine dulls the effects of methotrexate compared with caffeine doses of less than 120 mg per day. A typical cup of brewed coffee contains around 120 mg of caffeine.
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