Caffeine doesn't weaken arthritis drug's effects

NEW YORK (Reuters Health) - Caffeine does not appear to impair the effectiveness of methotrexate for treating rheumatoid arthritis (RA), Boston researchers report.

Methotrexate is the most commonly prescribed drug for slowing the progression of RA. It may exert some of its anti-inflammatory effects by boosting tissue levels of a protein called adenosine. Given that caffeine can block the cell receptors that adenosine acts on, it is possible that it could also blunt methotrexate's effects.

Studies in rats have indeed found that high doses of caffeine weakened methotrexate's actions, while some human studies have suggested it could have a similar effect in people.

To investigate, Dr. Elizabeth Benito-Garcia and colleagues from Brigham and Women's Hospital and Harvard Medical School divided 264 patients with RA who were taking methotrexate into three roughly equal groups based on their caffeine consumption.

Their intake averaged about 212 milligrams daily, or just over 1.5 cups of coffee. People in the highest caffeine consumption group took in 422 mg of caffeine a day, or a bit more than the amount contained in three cups of coffee.

People in the moderate to high caffeine consumption groups did show higher disease activity scores and physician assessment scores, as well as more swollen joints, on average, but these differences were not statistically significant.

Caffeine intake in the study participants may not have been high enough to impact methotrexate's effectiveness, Benito-Garcia and her colleagues note in an article in the Journal of Rheumatology. They think additional large studies looking at the impact of caffeine on methotrexate would be worthwhile.

SOURCE: Journal of Rheumatology, July 2006.