Sleep quality and the metabolic syndrome: the role of sleep duration and lifestyle.

Background: This study examined the association between sleep quality and the metabolic syndrome and whether if it is independent of sleep duration and if it can be explained by lifestyles linked to sleep quality.

Methods: Cross-sectional study conducted from 2008 to 2010 with 10 342 individuals representative of the population aged ≥18 years in Spain. Poor sleep quality was ascertained through self-reported difficulty falling asleep, difficulty maintaining sleep and sleeping pill consumption. Metabolic syndrome was defined according to the recent harmonized definition. Analyses were conducted with logistic regression and adjusted for the main confounders.

Results: Difficulty falling asleep was associated with higher frequency of metabolic syndrome after adjustment for sociodemographic variables, lifestyle and diagnosed morbidity [odds ratio (OR) = 1.25; 95% confidence interval (CI) = 1.06-1.47]. The association was slightly attenuated after further adjusting for sleep duration (OR = 1.23; 95% CI = 1.04-1.46) and held after additional adjustment for energy intake, adherence to a Mediterranean dietary pattern, energy spent in physical activity and time watching TV (OR = 1.20; 95% CI = 1.01-1.42). No associations were found between metabolic syndrome and other sleep quality indicators. Difficulty falling asleep was associated with high blood pressure in the fully adjusted analyses (OR = 1.17; 95% CI = 1.00-1.37) but not with the rest of components of metabolic syndrome.

Conclusions: Difficulty falling asleep is associated with metabolic syndrome and, in particular, with high blood pressure. This association is independent of sleep duration and is not due to lifestyles related to poor sleep. This finding should be replicated in prospective studies using objective sleep measures; also, the influence of antihypertensive and lipid-lowering drug treatment on this association should be further studied.