Papers of the Week

Evening chronotype individuals experience pain more often than morning chronotypes, but relationships with pain sensitivity have rarely been studied. We examined whether chronotype is associated with pressure pain sensitivity, with special reference to mental health disorders, insomnia, and chronic musculoskeletal (MSK) pain as potential moderating factors. The study sample consisted of members of the Northern Finland Birth Cohort 1966 (NFBC1966) aged 46. Pressure pain threshold and tolerance were measured via the standardized protocol, categorized as lowest quartile vs others. Chronotype (morning [M; the reference], intermediate [I], and evening [E]) was defined using the short Morningness-Eveningness questionnaire. Sex-stratified binary logistic regression models were separately adjusted for education, body mass index, long-term diseases (fully adjusted model) and for mental health disorders, insomnia, and chronic MSK pain (a residual confounding analysis). Interaction terms (chronotype⁎mental health/insomnia/chronic MSK pain) were tested. The study had 2132 males and 2830 females. The E-type males had 1.5-fold odds of having a low pain threshold (fully adjusted OR 1.45, 95% CI 1.05-2.00) and pressure pain tolerance (fully adjusted OR 1.47, 1.07-2.02), in comparison to M-types. Having a mental health disorder intensified the association with low pain threshold fourfold (4.06, 1.56-10.6). Being an E-type female was also associated with a low pain threshold, but the association was statistically non-significant (fully adjusted OR 1.18, 0.90-1.53). No statistically significant interactions were found among females. These results emphasize the role of chronotype in pain sensitivity and add understanding of pain experience in a light of innate circadian types. PERSPECTIVE: Male evening chronotypes are more sensitive to pain than morning chronotypes. Diagnosed mental health disorders in particular indicate a low pain threshold for evening chronotype males.