Excessive daytime sleepiness: an emerging marker of cardiovascular risk

Abstract

Excessive daytime sleepiness (EDS) is classically viewed as a consequence of insufficient sleep or a symptom of sleep disorders. Epidemiological and clinical evidence have shown that patients reporting EDS in tandem with sleep disorders (e.g., obstructive sleep apnoea) are at greater cardiovascular risk than non-sleepy patients. While this may simply be attributable to EDS being present in patients with a more severe condition, treatment of sleep disorders does not consistently alleviate EDS, indicating potential aetiological differences. Moreover, not all patients with sleep disorders report EDS, and daytime sleepiness may be present even in the absence of any identifiable sleep disorder; thus, EDS could represent an independent pathophysiology. The purpose of this review is twofold: first, to highlight evidence that EDS increases cardiovascular risk in the presence of sleep disorders such as obstructive sleep apnoea, narcolepsy and idiopathic hypersomnia and second, to propose the notion that EDS may also increase cardiovascular risk in the absence of known sleep disorders, as supported by some epidemiological and observational data. We further highlight preliminary evidence suggesting systemic inflammation, which could be attributable to dysfunction of the gut microbiome and adipose tissue, as well as deleterious epigenetic changes, may promote EDS while also increasing cardiovascular risk; however, these pathways may be reciprocal and/or circumstantial. Additionally, gaps within the literature are noted followed by directions for future research.

Keywords: hypertension; inflammation; obesity.

Figure 1.

Cox hazard functions for cardiovascular mortality by daytime sleepiness adjusted for comorbidities (e.g., type 2 diabetes), cardiovascular risk factors (e.g., body mass index), socioeconomic factors (e.g., income), and sleep duration as well as sleep disorders. Sleepiness was quantified by the frequency individuals felt overly sleepy within a month; >1 (no excessive daytime sleepiness, EDS), 1-4 (mild EDS), or 5-30 (EDS). HR, hazard ratio; CI, confidence interval. Reprinted with permission from Li et al.

Figure 2.

Theoretical framework of mechanisms promoting excessive daytime sleepiness which likely contribute to the increased cardiovascular risk of individuals reporting sleepiness. Grey lines indicate mechanisms that may be bidirectional.