Circadian syndrome is inversely associated with lung function and cardiorespiratory fitness in the general population

Background A disruption of the circadian clock results in dysregulation of immune responses, inflammatory processes, and oxidative stress, which favors the development of chronic lung diseases and impairs cardiorespiratory fitness (CRF). Purpose We investigated the relationship between circadian syndrome (CircS) and lung health and CRF in a population-based setting. Methods For this study, we used data from the population-based "Study of Health in Pomerania" (SHIP-TREND-0) including n=2,496 (49.4% female; median age 59 years with CircS and 50 years without CircS). Lung function and CRF were assessed by pulmonary function testing and cardiopulmonary exercise testing (CPET), respectively. Lung disease was ascertained by self-report. CircS was determined based on high waist circumference ≥ 88 cm (female) and ≥ 102 cm (male); high triglycerides (≥ 1.7 mmol/l) or lipid therapy; low HDL-cholesterol (≤ 1.3 mmol/l); high blood pressure (≥ 130/80 mmHg) or antihypertensive therapy; HbA1c ≥ 5.7% or antidiabetic therapy; average sleep duration ≤ 6 h and PHQ-9 sum score ≥ 5. The cohort was divided into individuals with CircS (605) and those without (1,864). To evaluate the association between CircS and both lung health and CRF, linear regression models adjusted for age, smoking status, years of education, and alcohol consumption were used. Results The cohort with CircS was overall older, included more men, had a lower educational level and lower alcohol consumption, and higher BMI. A higher proportion of subjects with CircS reported lung disease. The presence of CircS was associated with a 4.17% (95% CI: -6.82 to-2.54) lower forced expiratory volume in the first second, a 6.41% (95% CI: -8.18 to -2.81) lower forced vital capacity, and a 4.62% (95% CI: -6.45 to -2.81) lower percent-predicted peak oxygen uptake. Conclusion Our population-based study showed an inverse association between CircS and lung health, as well as CRF. Given that CircS is defined in part by average sleep duration and the PHQ-9 score, these findings are consistent with the hypothesis that circadian rhythm disruption may be associated with reduced pulmonary and cardiorespiratory health.