DEAR DR. BLONZ: Coffee is a part of my morning routine, but I have read that there might be an association between coffee and rheumatoid arthritis. The thought of this is giving me a real headache. I usually have a cup in the morning and another with lunch. My parents both have osteoarthritis, and I certainly don't want to take steps down any road that might lead to that. -- K.D., San Diego
DEAR K.D.: Don't toss your coffee beans yet. There has been research reporting a potential connection between decaf coffee-drinking and the risk of rheumatoid arthritis -- a form of arthritis involving the immune system. This is not the same as osteoarthritis (see tinyurl.com/jga42vh for more on the different forms). The type of research you reacted to was epidemiological, often referred to as a "population study." Such research reports coincidences between the factors it measures, but not causation: It doesn't tell you what, if anything, is causing what.
In this case, the study, in the January 2002 issue of the journal Arthritis and Rheumatism, reported an increased risk of rheumatoid arthritis in women drinking more than four cups of decaffeinated coffee per day. It did not conclude that drinking decaf causes rheumatoid arthritis.
My favorite example of the limits of epidemiological research was a finding that physicians who eat meat and drink alcohol have a significantly lower risk of being killed in a plane crash. So, should all docs have a burger and a beer before every flight? Of course not. But if there is nothing going on, why would this relationship be found? It turns out to be one of the quirks of research involving large amounts of data, and it is the reason we need more than a mere statistical relationship before giving full credence to results.
With the coffee study, for example, there might be other factors that have yet to be considered. Next steps might be replication with other populations to see if the relationship held. If so, there could then be an examination of other variables, such as method of coffee preparation or other dietary and lifestyle factors, that might be at play.
That 2002 study was countered by a subsequent study in the November 2003 issue of the same journal. This one failed to support the relationship between coffee, tea and rheumatoid arthritis. A November 2014 study in the journal Clinical Rheumatology performed a meta-analysis on the relationship between coffee (or tea) consumption and the risk of rheumatoid arthritis. A meta-analysis is one in which multiple studies, all meeting specific criteria, are combined and their data viewed collectively. This study reported there was a relationship between a high coffee consumption (four or more cups per day), and the risk of rheumatoid arthritis -- but only with individuals having a positive blood test for rheumatoid arthritis. For those with a negative test, no relationship was found.
The bottom line is that there is no evidence that drinking coffee raises risk of osteoarthritis (the type your parents have). Coffee has also not been shown to cause rheumatoid arthritis, but for those who already have this condition, there may be a reason to limit consumption. It is certainly something best discussed with your physician or rheumatologist.
Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to firstname.lastname@example.org. Due to the volume of mail, personal replies cannot be provided.