Sleeping more than 9 hours per night, taking long naps during the day, and poor sleep quality are all independently linked to an increased stroke risk, particularly ischemic events, new research suggests.
Results of a large, prospective cohort study show individuals who slept 9 or more hours per night had a 23% increased risk of stroke compared to those who slept from 7 hours to less than 8 hours. In addition, individuals who took mid-day naps lasting 90 minutes or more had a 25% increased stroke risk.
“We wish physicians suggest people, especially middle-aged and older adults, pay more attention to their time spent in bed…and to maintain good sleep quality,” senior author Xiaomin Zhang, MD, PhD, Tongji Medical College, Huazhong University of Science and Technology in Wuhan, China.
Appropriate duration of sleep and napping, as well as good sleep quality, may complement other behavioral interventions for stroke prevention, Zhang added.
The study, which was funded by the National Natural Scientific Foundation and National Key Research and Development Program of China, was published online December 11 in Neurology.
Stroke Risk by Subtype
These latest findings add to a growing body of evidence showing a J- or U-shaped curve tied to sleep and stroke risk in which those who report the longest and shortest sleep duration are at highest risk for stroke.
However, the researchers note that these findings remain controversial.
Up until now most previous research has examined the association between sleep duration and stroke regardless of mid-day napping. In addition, the investigators note that few studies have examined the potential link between sleep duration and stroke subtypes.
Previous research from Zhang and colleagues showed a 33% increased risk of coronary heart disease and a 25% increased likelihood for incident stroke in individuals who slept 10 hours or more or napped 90 minutes or longer.
“The similar finding suggests the importance of moderate napping and sleeping duration and maintaining good sleep quality not only to prevent coronary heart disease but also to prevent stroke,” Zhang said.
To learn more, the investigators analyzed data on 31,750 participants who were an average age of 61.7 years. All were retired employees from Dongfeng Motor Corporation.
Participants completed questionnaires about sleep duration, sleep quality, and daytime napping in the previous 6 months. Researchers also checked subsequent ICD-10 codes for a first incident stroke.
Over the 6-year follow-up, there were 1438 confirmed strokes. These diagnoses were based on clinical symptoms and CT or MRI scans. Another 119 strokes were deemed “probable” because medical records were unavailable to confirm insurance records or information provided by telephone.
Participants who reported sleeping 9 hours or more per night or napping 90 minutes or longer were more likely to be men, less educated, current smokers and drinkers, and to be physically inactive compared with the shortest sleepers.
Table. Nighttime Sleep and Total Stroke Risk
| Sleep duration | Adjusted Hazard Ratio | 95% CI |
|---|---|---|
| < 6 hours | 1.10 | 0.69 – 1.75 |
| 6 to < 7 hours | 1.15 | 0.93 – 1.43 |
| 7 to < 8 hours | (reference) | (reference) |
| 8 to < 9 hours | 1.03 | 0.91 – 1.17 |
| ≥ 9 hours | 1.23 | 1.07 – 1.41 |
A total of 1151 definite strokes were ischemic and another 287 events were hemorrhagic.
Sleep quality also modified the association with stroke risk. Compared with participants who reported good sleep quality, those with poor sleep quality at night had an elevated risk for total stroke (hazard ratio [HR], 1.29; 95% CI, 1.09 – 1.52), ischemic stroke (HR, 1.28; 95% CI, 1.05 – 1.55), and hemorrhagic stroke (HR, 1.56; 95% CI, 1.07 – 2.29).
Because the study was prospective, researchers were able to assess sleep duration changes over time. They found that participants who consistently slept 9 or more hours per night, as well as those who switched from 7 to 9 hours to 9 hours or more had a 36% to 44% higher risk of incident stroke.
Table. Daytime Napping and Total Stroke Risk
| Napping Duration | Adjusted Hazard Ratio | 95% CI |
|---|---|---|
| No napping | 1.02 | 0.87 – 1.20 |
| 1-30 minutes | (reference) | (reference) |
| 31-60 minutes | 1.09 | 0.93 – 1.28 |
| 61-90 minutes | 1.13 | 0.94 – 1.37 |
| > 90 minutes | 1.25 | 1.03 – 1.53 |
Long sleep duration, long midday napping, and poor sleep quality were independently and jointly associated with a higher risk of incident stroke, the researchers note.
Participants age 65 and older and those with hypertension, hyperlipidemia, or diabetes had a “more pronounced” risk of incident stroke associated with longer sleep duration. In addition, overweight individuals had a more notable risk for stroke when they reported daytime napping longer than 90 minutes.
“It is plausible to suppose that these traditional cardiovascular risk factors may amplify the detrimental effect of long sleep duration or napping on stroke incidence,” the researchers write.
Additional studies are needed to replicate the findings, the researchers note.
Going forward, Zhang said her team wants to explore the potential link between sleep, genetic status, and risk of cardiovascular disease. Such research could lead to specific gene-targeted guidelines for healthy sleep durations in specific subpopulations, she said.
Kudos, Caveats
Commenting on the findings Logan Schneider, MD, clinical instructor at the Stanford Center for Sleep Science and Medicine in California, said the findings strengthen the well-known association between sleep and health.
“Most reassuringly, the results are consistent with the awareness that sleep duration may be an indicator of increased health risks,” said Schneider, a fellow of the American Academy of Neurology.
Although the study looked at associations and not causality, relied on subjective reports of sleep duration, and assessed a relatively selective population, “it still did a great job of accounting for a lot of aspects that could confound the findings, and did so in a very large population.”
“Ultimately, they identified that excessive sleep of any kind — napping too much and/or sleeping too much at night — seems to be associated with a higher risk of stroke,” Schneider said.
The finding of increased stroke risk when individuals transitioned over time from average to longer sleepers “is particularly interesting because the normal trend in sleep duration is slightly lower as we age, so going in the opposite direction is particularly telling,” he said.
“I want to emphasize that the message is not that you should avoid sleeping longer because it increases your risk of stroke. You need to sleep as much as is necessary to wake refreshed and remain alert throughout the day,” Schneider said.
“When sleep need is unusually long,” he added, “people should wonder if there is an underlying problem of sleep or another medical condition that may be causing an increased need for sleep.”
Neurology. Published online December 11, 2019.
