At more than four million person-years, the Nurses’ Health Study provides valuable information.
“My rheumatoid is due to something I’ve done, doctor?”
Some of us have been in practice for many years, and my usual response to this question was a resounding but reassuring, “No.”
There was data suggesting that smoking interacted with genetic factors and some professional associations (coal miners for example), but these seemed rare in my patients and the usual advice was to stay as active as possible, quit smoking if you are CCP positive (in particular) and perhaps eat less saturated fat. In general, I suggested that most of these (aside from quitting, according to the CORRONA RA database) wouldn’t do much good.
However, in recent years there have been multiple papers on this topic that I had a vague knowledge of.
The authors of the featured article have previously published individual articles on each of the five risk factors, doing the original salami-cutting exercise. Now, they decided to put them all together, which would have been the best thing to do in the first place, but academics will be academics (even if the last article would have made a big impact if it had been published first). This is a discussion I often have with my students: the first goal is to make a difference in a real sense, not just on your CV. To be fair, these studies are difficult to perform, since rheumatoid cohort studies require millions of patient-years of observation.
The study discussed here is from the Nurses Health Study, which is predominantly white US women with high levels of education. This may be a problem as RA has a socioeconomic gradient, however the study meets Rothman’s generalizability criteria.
The study is extensive, with more than four million person-years and more than 1,000 incident cases of RA. They can measure some things very accurately, such as BMI, smoking, and antibody status. Diet and physical activity are assessed using a questionnaire, which is rather murky and makes them prone to regression dilution bias (ie the actual association may actually be stronger than reported).
Building on previous articles, they identified five risk factors: BMI (healthy range), alcohol (one drink a day), activity (30 minutes a day), diet (better 40%!), and never smoking. These were all boiled down to binary measures, which seems a bit arbitrary to me, especially for diet, and lessens the impact.
However, the results were surprising because having all five was associated with a much lower risk of RA (75% for HIV-positive and 58% for HIV-negative).
There was also a dose-response association, and the calculated population attributable risk (PAR) was 34%. This is the amount that is potentially reversible if everyone did the right thing. BMI (harmful), alcohol (protective) and smoking were major contributors, with little independent effect of diet and activity (perhaps due to how they were measured).
These are the best data we will get on these topics, and I have changed my practice to include some conversations with my patients.
Hahn J, Malspeis S, Choi MY, Stevens E, Karlson EW, Lu B, Cui J, Yoshida K, Kubzansky L, Sparks JA, and Costenbader KH (2022). Association of healthy lifestyle behaviors and the risk of developing rheumatoid arthritis among women. Res. for arthritis care. doi.org/10.1002/acr.24862
Graeme Jones is professor of rheumatology and epidemiology at the Menzies Institute for Medical Research.
Source: news.google.com