Short sleep duration aggravates mortality risk metabolic syndrome
Impact of the Metabolic Syndrome on Mortality is Modified by Objective Short Sleep Duration
The metabolic syndrome (MetS) is associated with high healthcare costs, increased risk of all-cause mortality and sleep disordered breathing (SDB), while its association with sleep duration is less clear [1-3]. Objective short sleep duration may play a role as an effect modifier in increasing cardio-metabolic morbidity and mortality through various mechanisms, including increased cortisol, catecholaminergic activity and impaired heart rate variability [4-6]. However, studies examining this in relation to MetS have reported modest and inconsistent effects [7,8]. The subjectivity of measures of sleep is an important limitation in these studies.
In this study, the effect modification of objective sleep duration on the increased risk of all-cause and cardiovascular/cerebrovascular (CVD/CBV) mortality associated with MetS was evaluated in a random, general population sample (Penn State Adult Cohort, final n=1344, follow-up 16.6 yrs). Five cardio-metabolic components were evaluated: obesity, hypercholesterolemia, hypertriglyceridemia, glucose dysregulation and high blood pressure. For this study, a first phase was conducted by telephone interviews and in the second phase, individuals were randomly selected and studied in a sleep laboratory.
- Individuals with MetS had a significantly higher crude mortality rate compared with those without MetS (32.7% vs. 15.1%; P<0.01).
- Objective short sleep duration was associated with all 5 cardio-metabolic components (all P<0.05).
- The multivariable-adjusted risk of all-cause mortality associated with elevated fasting glucose (HR 1.38, 95% CI 1.10–1.76) and elevated blood pressure (HR 1.43, 95% CI 1.12–1.84, both P<0.01).
- When at least 3 of cardio-metabolic components were present, all-cause mortality reached significance (HR 1.75, 95% CI 1.18–2.61, P<0.01), with graded increase in effect size for subjects with 4 or 5 cardio-metabolic components (HR 1.79, 95% CI 1.01–3.20, P=0.04 and HR 2.24, 95% CI 1.32–3.79, P<0.01 respectively).
- After adjusting for all covariates, individuals with MetS showed a 2-fold higher risk of all-cause mortality (HR 1.73, 95% CI 1.40–2.14, P<0.01) and CVD/CBV mortality (HR 1.92, 95% CI 1.35–2.74, P<0.01) compared with those without MetS.
- The multivariable-adjusted risk stratified by objective short sleep duration, showed that the HRs of all-cause mortality associated with MetS were 1.29 (95% CI 0.89–1.87) and 1.99 (95% CI 1.53–2.59) for subjects who slept ≥6 and <6 hours, respectively.
- The risk of CVD/CBV mortality associated with MetS as a function of objective short sleep duration was 1.49 (95% CI 0.75–2.97) and 2.10 (95% CI 1.39–3.16) for subjects who slept ≥6 and <6 hours, respectively.
- The survival functions for participants who slept ≥6 with and without MetS were similar (P=0.19 and P=0.25, for all-cause and CVD/CBV mortality, respectively), but the survival functions were significantly worse in those with MetS among participants who slept <6 hours (both P<0.01).
- Participants with MetS who only had obesity, hypercholesterolemia and hypertriglyceridemia (n=34) were not at significant increased risk of mortality as compared to those without MetS (HR 0.40, 95% CI 0.02–6.19) and thus were merged into 1 reference group. The risk of all-cause mortality was significantly increased in those participants with MetS clusters of (1) elevated blood pressure and 2 or 3 other components, but without elevated fasting glucose (HR=1.75; 95% CI=1.16–2.64), (2) elevated fasting glucose and BP with 1 or 2 other components (HR=1.46; 95% CI=0.96–2.32), and (3) with both fasting glucose and BP elevated (HR=1.76; 95% CI=1.40–2.22).
- The multivariable-adjusted HRs of all-cause mortality associated with the MetS cluster 2 were 1.50 (95% CI 0.99–2.38) and 1.93 (95% CI 1.45–2.54) for subjects who slept ≥6 and <6 hours, respectively.
- The risk of CVD/CBV mortality associated with MetS cluster 2 were 1.93 (95% CI 0.86–4.32) and 2.10 (95% CI 1.36–3.24) for subjects who slept ≥6 and <6 hours, respectively.
The risk of mortality associated with MetS was found to be significantly higher in individuals with objective short sleep duration. The risk was highest in those with high blood pressure and elevated fasting glucose. These findings suggest that lengthening of sleep may improve the prognosis of individuals with MetS.