Association between self-reported napping and risk of cardiovascular disease and all-cause mortality: A meta-analysis of cohort studies

The study investigates whether daytime napping, particularly its duration, is associated with risks of all-cause mortality and cardiovascular disease (CVD) in adults. While napping can mitigate risks from insufficient sleep and has benefits for attention, efficiency, and stress reduction, evidence also links napping to higher risks of certain cancers and obesity. Napping affects the autonomic and central nervous systems and may disrupt circadian rhythms, suggesting complex ties to mortality and CVD. Prior meta-analyses largely focused on nighttime sleep, and findings on daytime napping are inconclusive. Earlier syntheses indicated napping predicts overall mortality but not cardiovascular mortality, while more recent work suggests longer naps (>60 minutes) increase both risks. Given conflicting and new evidence, this meta-analysis aims to provide an updated, comprehensive assessment of adult nap duration and risks of all-cause mortality and CVD.

Previous meta-analyses have reported mixed findings. A 2015 meta-analysis of seven studies suggested that daytime napping predicts all-cause mortality but not cardiovascular mortality. A dose-response meta-analysis in 2020, spanning 13 studies, found that prolonged nap duration (>60 minutes) was significantly associated with increased risks of all-cause mortality and CVD. Several recent cohort studies (published 2016–2024) with varying conclusions were not included in earlier analyses, prompting the need for an updated synthesis. The current work integrates seven additional recent studies to refine understanding of nap duration effects and potential gender differences reported inconsistently across cohorts.

The meta-analysis followed PRISMA guidelines and was registered in PROSPERO (CRD42024547547). Database searches (PubMed, Cochrane Library, Embase, Web of Science) were conducted from inception to April 30, 2024, using MeSH and keywords related to napping and cardiovascular/mortality outcomes, without language restriction. Reference lists of eligible studies were screened. Eligibility criteria: population-based cohort studies of adults (≥18 years) that assessed daytime napping and reported all-cause or cause-specific mortality and/or CVD outcomes with HR/OR and 95% CI estimates. Exclusions: reports, reviews, conference abstracts, duplicates, and studies lacking effect estimates. Study selection involved independent screening by two reviewers (titles/abstracts, then full text), with disagreements resolved by a third reviewer. Data extraction was performed by two reviewers using a standardized table, capturing author, year, country, follow-up duration, sample size, cohort characteristics, age, napping assessment, subgroup analyses, confounder adjustments, and Newcastle-Ottawa Scale (NOS) scores; discrepancies were resolved by a third reviewer. Risk of bias was assessed via NOS across selection, comparability, and outcome domains (scores 0–9). Statistical analysis used DerSimonian–Laird random-effects models to pool HRs comparing nappers to non-nappers (reference). When multiple adjusted estimates were available, the most adjusted was selected. Subgroup analyses were conducted by gender. Sensitivity analyses (leave-one-out) assessed robustness. Publication bias was evaluated using funnel plots and Egger’s test. Analyses were conducted in Stata 14.0.

- Studies included: 21 cohort studies across 11 countries (publication years 1996–2024), total participants ≈374,306; follow-up 4–18 years; study quality moderate to high (mean NOS 7.52±0.87). - All-cause mortality: Nappers vs. non-nappers had higher mortality risk (HR 1.28, 95% CI 1.18–1.38; I²=38.8%; P<0.001). Nap duration effects: <1 hour showed no association (HR 1.00, 95% CI 0.90–1.11; I²=62.6%; P=0.971). ≥1 hour was associated with increased mortality (HR 1.22, 95% CI 1.12–1.33; I²=40.0%; P<0.001). - Cardiovascular disease (CVD) risk: Nappers vs. non-nappers had higher CVD risk (HR 1.18, 95% CI 1.02–1.38; I²=87.9%; P=0.031). Nap duration effects: <1 hour showed no significant association (HR 1.03, 95% CI 0.87–1.12; I²=86.4%; P=0.721). ≥1 hour was associated with increased CVD risk (HR 1.37, 95% CI 1.09–1.71; I²=68.3%; P=0.007). - Gender subgroup: No significant associations for men or women for all-cause mortality or cardiovascular mortality (men: all-cause HR 1.04, 95% CI 0.81–1.33; CVD HR 1.10, 95% CI 0.87–1.40. women: all-cause HR 1.07, 95% CI 0.83–1.38; CVD HR 1.08, 95% CI 0.76–1.54). - Sensitivity analyses: No single study reversed pooled effects; results robust. Publication bias: Funnel plots and Egger’s test indicated no significant bias.

Findings demonstrate that daytime napping is associated with increased risks of all-cause mortality and CVD, and that nap duration is critical: short naps (<1 hour) show no adverse association, whereas longer naps (≥1 hour) are linked to increased risks. These results update and expand prior evidence, reconciling conflicting conclusions by including recent cohort studies. Potential mechanisms include postural changes upon waking that may promote prothrombotic states, increased sympathetic activity and heart rate after naps, and links between daytime sleepiness and cardiometabolic diseases. Excessive napping has also been associated with diabetes, Alzheimer’s disease, cancer, and obesity, potentially via effects on brain structure, insulin sensitivity, and circadian disruption. While gender did not modify associations in pooled analyses, individual cohorts have reported gender- and age-specific effects, suggesting possible heterogeneity that warrants further study. The absence of risk elevations for naps <1 hour is consistent with some reports that short naps may be neutral or even beneficial; finer categorization of short nap durations could clarify dose-response effects.

Prolonged daytime napping (≥1 hour) is associated with increased risks of all-cause mortality and cardiovascular disease, whereas shorter naps (<1 hour) show no significant association. These findings underscore nap duration as an important consideration in evaluating mortality and cardiovascular risk. Future research should elucidate pathophysiological mechanisms through longitudinal and genetic studies, assess regional and racial differences, refine dose-response relationships for short naps, and conduct prospective studies to validate the predictive value of nap duration for adverse outcomes.

- Limited subgroup analyses by region and race due to insufficient data. - Inclusion restricted to cohort studies; lack of case-control and cross-sectional designs may limit methodological diversity. - Potential variability in lifestyle and sleep habits across countries may influence findings. - Meta-analysis did not perform covariate meta-regression; although individual cohorts adjusted for confounders, residual confounding is possible. - Nap duration assessed via questionnaires/interviews, introducing measurement error and recall bias. - High heterogeneity in some pooled analyses (particularly CVD outcomes and short nap duration subgroups).