Long daytime napping over 1 hour per day is associated with increased risk of diabetes

Abstract

Introduction: Daytime napping or siesta is a prevalent lifestyle practice in many populations. It is thought to be health-promoting, with beneficial effects to improve the working effectiveness, mental health and functioning in daytime. It is also regarded as a way to counteract the effects of sleep disorders (e.g. insomnia and sleep apnea). However, recently published meta-analyses suggested that daytime napping might be deleterious to health. In recent years, sleep pattern has been widely accepted as a modifiable risk factor for the development of diabetes mellitus (DM). Nevertheless, conflicting results were observed across different studies, especially in the association between short daytime napping (i.e. daytime napping less than 1 hour per day) and DM risk. Therefore, in this study, we aimed to perform a systematic review and meta-analysis to synthesize the association of daytime napping and its duration with risk of DM in both cross-sectional and cohort studies. Materials and methods: The electronic databases of Embase, Medline, Pubmed and Web of Science were searched. Relevant studies were extracted by two reviewers independently. The associations between daytime napping (irrespective of duration), long nap (≥1 hour/day) and short nap (< 1 hour/day), and risk of DM were assessed according to study types. Overall estimates were pooled using either fixed- or random-effect with inverse variance meta-analysis. Heterogeneity of included studies was assessed using the I2 test and possible cause of the heterogeneity was examined by meta-regression analyses. Results: Ten studies (4 cross-sectional and 6 longitudinal cohort) comprising a total of 304,885 individuals and 20,857 cases of DM were included in the systematic review, with an average napping prevalence of 47%. Nappers were found to have increased risk of DM in both cross-sectional and cohort studies. However, significant heterogeneity was present. Long nap (≥1 hour/day) was associated with both prevalent and incident DM; in particular, those with a daily nap over 1 hour had a 31% increased risk of developing DM during follow-up (95% confidence interval: 2-67%). Conversely, no such association was found in individuals with short naps (< 1 hour/day) in cohort studies. Conclusions: In conclusion, our study added fuel to the ongoing debate on the impact of daytime napping on DM risk. Although our findings suggested that daytime napping over 1 hour per day was associated with a 31% increased DM risk, the heterogeneity of included studies precluded us to make a definite conclusion. Since the nature of the association is not clear, further studies with objective assessment of daytime napping on DM risk, covering participants from more age groups and ethnicities, are needed to confirm the findings. Our study also supports that daytime napping-related measures should be included in sleep studies.