Relationship between sleep characteristics and markers of inflammation in Swedish women from the general population

Systemic inflammation is thought to mediate the link between sleep and cardiovascular outcomes, but previous studies on sleep habits and inflammation markers have found inconsistent results. This study investigated the relationship between sleep characteristics and C-reactive protein (CRP), interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF alpha). A representative sample of 319 Swedish women was randomly selected from the general population for in-home polysomnography, sleep questionnaire and blood samples. As variables were highly correlated, principal component analysis was used to reduce the number of original variables. Linear regression with log-transformation of the outcomes (lnCRP, lnIL-6 and lnTNF alpha) and quantile regression were fitted to estimate cross-sectional relationships. Multivariable linear regression models suggested a significant association of insomnia symptoms (self-reported) with higher lnCRP levels (beta = 0.11; 95% confidence interval [CI] = 0.02; 0.21), but not with lnIL-6 and lnTNF alpha. From quantile regression analysis we found that a high non-restorative index (subjective) and insomnia symptoms (self-reported) were associated with higher values of CRP, especially in the highest quantiles of the CRP distribution (90th percentile: beta = 0.71; 95% CI = 0.17; 1.24. beta = 1.23; 95% CI = 0.44; 2.02, respectively). Additionally, higher amounts of rapid eye movement (REM) sleep were associated with lower CRP values (90th percentile: beta = -0.80; 95% CI = -0.14; -1.46). In conclusion, sleep disturbances (self-reported), specifically difficulties maintaining sleep and early morning awakenings, but not sleep duration (neither subjective nor objective), were associated with higher CRP levels. No association was found with IL-6 or TNF alpha. Elevated REM sleep was associated with lower CRP levels. The results suggest that inflammation might be an intermediate mechanism linking sleep and health in women.