Abstract
OBJECTIVES: Rheumatoid arthritis (RA) patients show an earlier circadian rhythm (i.e. serum melatonin peaks earlier during the night, indicating an earlier timing of the internal circadian pacemaker). In the current study, we examined whether the chronotype, which is influenced by the circadian rhythm, is also earlier. In addition, we explored whether chronotype is related to disease activity and patient-reported outcomes. METHODS: The chronotype (Munich Chronotype Questionnaire) of patients with RA (n = 121; mean age 60 years, 73% female) was compared with that of subjects from the general population (norm group; n = 1695) with a one-sample t test. In addition, we investigated chronotype in relation to disease activity (Disease Activity Score; DAS), reported morning stiffness, fatigue (Checklist Individual Strength), and health-related quality of life (RAND-36). RESULTS: The chronotype of patients with RA was, on average, 23 min (95% CI, 15 to 31 min) earlier than that of the norm group (t(115) = - 5.901, p < 0.001, d = 0.55). Chronotype was not related to disease activity or patient-reported outcomes (p > 0.05). CONCLUSION: As expected, chronotype was earlier in RA patients. However, in this correlational study, chronotype was not related to disease activity or patient-reported outcomes. An experimental study is needed to examine whether delaying the circadian rhythm has a positive influence on these outcomes. This insight could improve our understanding of the pathophysiology of RA and contribute to exploring new treatment possibilities. Key Points • This is the first study examining chronotype in patients with rheumatoid arthritis, and how chronotype relates to disease activity and patient-reported outcomes. • We found an earlier chronotype in patients with rheumatoid arthritis than in subjects from the general population. • In this correlational study, chronotype was not related to disease activity or patient-reported outcomes. An experimental study is needed to examine whether delaying the circadian rhythm positively influences these outcomes.