Sleeping ≥9 hours at night or >90 minutes during the day increases risk of stroke
A large prospective Chinese cohort study has found long sleep duration (≥9 hours/night) and long mid-day napping (>90 minutes) to be significantly associated with a higher risk of ischaemic stroke.
Researchers analyzed data from 31,750 participants (female, n=17,754; average age, 61.7 years) from the Dongfeng-Tongji cohort. During an average 6.2 years of follow-up, 1,438 definite stroke cases were documented (1,151 ischaemic and 287 haemorrhagic). Nearly a quarter (23.9 percent) of study participants reported sleeping ≥9 hours/night and 7.6 percent reported mid-day napping of >90 minutes. [Neurology 2020;94:1-12]
Compared with sleeping for 7 to <8 hours/night, the multivariate-adjusted hazard ratios (maHRs) of total stroke were 1.10 (95 percent confidence interval [CI], 0.69 to 1.75) for sleeping <6 hours/night, 1.15 (95 percent CI, 0.93 to 1.43) for sleeping 6 to <7 hours/night, 1.03 (95 percent CI, 0.91 to 1.17) for sleeping 8 to <9 hours/night, and 1.23 (95 percent CI, 1.07 to 1.41) for sleeping ≥9 hours/night, respectively.
Participants who persistently reported sleeping ≥9 hours/night and those who switched from sleeping 7–9 hours to ≥9 hours/night showed a 1.35-fold (95 percent CI, 1.01 to 1.82) and 1.44-fold (95 percent CI, 1.12 to 1.86) higher risk of incident stroke vs those who reported sleeping 7–9 hours/night throughout the study.
Compared with participants napping 1–30 minutes per day, the maHRs of total stroke were 1.02 (95 percent CI, 0.87 to 1.20) for those reporting no napping, 1.09 (0.93 to 1.28) for 31- to 60-minute naps, 1.13 (95 percent CI, 0.94 to 1.37) for naps of 61–90 minutes, and 1.25 (95 percent CI, 1.03 to 1.53) for naps >90 minutes, respectively.
When stratified by stroke subtypes, long night-time sleep and long day-time naps were associated with ischaemic stroke, but not haemorrhagic stroke. “It is unknown why long sleep duration might be associated with different stroke subtypes,” wrote the researchers. “The null results in our study might be attributed to the relatively small number of haemorrhagic stroke cases [n=78] in the long sleep group, resulting in a limited statistical power,” they suggested.
“Notably, the risk of incident stroke with long sleep duration appeared to be more pronounced in individuals who were ≥65 years old, and those with hypertension, hyperlipidaemia, or diabetes, while the association between napping >90 minutes and stroke incidence seemed to be more evident among persons who were overweight,” wrote the researchers. “It is plausible that these traditional cardiovascular risk factors may amplify the detrimental effect of long sleep duration or napping on stroke incidence.”
Compared with participants with good sleep quality, the HRs for total, ischaemic and haemorrhagic stroke were 1.29 (95 percent CI, 1.09 to 1.52), 1.28 (95 percent CI, 1.05 to 1.55) and 1.56 (95 percent CI, 1.07 to 2.29), respectively, for those with poor sleep quality at night. “Poor sleep quality increased the incident risk of ischaemic and haemorrhagic stroke separately,” noted the researchers.
Significant joint effects of sleeping ≥9 hours/night and napping >90 minutes (HR, 1.85; 95 percent CI, 1.28 to 2.66), and sleeping ≥9 hours/night and poor sleep quality (HR, 1.82; 95 percent CI, to 1.33 to 2.48) were observed on the risk of total stroke.
“Our results highlight the importance of appropriate and stable sleep duration, moderate mid-day napping, and maintaining good sleep quality for stroke prevention, especially in middle-aged and older adults,” concluded the researchers.