Short sleep duration aggravates mortality risk metabolic syndrome

Background

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.

Main results

• 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.

Conclusion

References

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