Women who work shift schedules or irregular hours are at significantly higher risk of developing rheumatoid arthritis (RA) than those who work regular daytime hours, according to a recent study presented at EULAR 2026.
“RA is a chronic inflammatory disease that is associated with both genetic factors and environmental exposures,” said the researchers. “Shift work, defined here as working outside regular day shifts, can cause circadian dysfunction and is considered a potential contributory factor to a range of pathological conditions, including chronic inflammation.”
Using data from the Malmö Diet and Cancer Study database, the researchers conducted a population-based health survey involving 30,447 participants to identify incident cases of RA. Of these, 305 participants (232 women and 73 men) who developed RA were identified and matched with 1,220 controls. Lifestyle factors, including shift work, smoking, and education, were collected using detailed questionnaires.
Among women, 32.9 percent of RA cases had a history of shift work compared with 26.3 percent of controls. However, in men, shift work was slightly less common among those with RA (29.5 percent) than among controls (34.1 percent). [EULAR 2026, abstract POS1309]
After adjusting for multiple variables, women who worked shifts had a 49-percent higher risk of developing RA than those working regular hours (odds ratio [OR], 1.49). Smoking (OR, 1.83) and a lower level of formal education (ORs, 2.94 [9–10 years] and 2.74 [≤8 years]) were also independent risk factors for RA in women.
In contrast, no significant associations were found between shift work, smoking, or education and risk of RA in men.
The difference in the effect of shift work between men and women was statistically significant (p=0.02).
Overall, this study provides evidence that shift work or inconvenient working hours were associated with an increased risk of developing RA in women, but not in men, compared with those with regular working hours.
“This may reflect effects on autoimmunity and inflammation of circadian rhythm dysregulation or other exposures related to irregular working hours in women,” the researchers noted.
This finding aligns with a previous study that found shift workers, especially among evening chronotypes, had a markedly higher risk of RA. This adds to the mounting evidence that circadian rhythms are a key factor in RA and adds strength to the idea that circadian misalignment, whether caused by shift work or an individual’s circadian preference through chronotype, may be crucial in RA development. [J Biol Rhythms 2023;38:510–518]