Does the weather really matter? A cohort study of influences of weather and solar conditions on daily variations of joint pain in patients with rheumatoid arthritis.

OBJECTIVE To explore how reported joint pain in patients with rheumatoid arthritis (RA) relates to weather and solar variables. METHODS A prospective cohort study was conducted in Norway on 36 patients with stable RA. Daily reports of pain in the morning on a visual analog scale for 84 consecutive days were correlated (using time-series methodology) with records of atmospheric and solar variables for the same days. RESULTS Pain was significantly associated with 3 or more external variables in 6 (17%) of the patients, with 1 or 2 external variables in 16 (44%) of the patients, and no associations were observed in 14 (39%) of the patients. The multivariate model explained between 19% and 64% of the variance in pain (R(2)) in the patients with associations to at least 3 weather/solar variables. The patients differed in the variables they responded to and in which direction, except for consistent negative associations between pain and ultraviolet light dose, and between pain and solar radio flux/sunspot count. The associations were mostly with same-day weather, but also lagged up to 3 days. We were not able to fit a statistically significant model at the group level. CONCLUSION Weather sensitivity seems to be a continuum and a highly individual phenomenon in patients with RA. In the present sample, pain was significantly associated with 3 or more weather variables in 1 out of 6 patients, for whom the magnitude of weather sensitivity might significantly influence pain reporting in clinical care and research.