Excessive daytime sleepiness linked with higher stroke risk

People who experience routine episode of dozing during the daytime may have a higher risk of stroke and other vascular events, according to a prospective, community-based cohort study of more than 2,000 people.

The risk of stroke also appeared to increase as the frequency of daytime dozing rose, suggesting a dose-response effect, reported at the International Stroke Conference 2008.

To investigate the relationship between daytime sleepiness (as a measure of underlying sleep disturbance) and stroke, associates used data from the multiethnic Northern Manhattan Study of 3,298 residents living in that part of the island. The study has been ongoing since 1993 and stopped enrollment in 2002, but the Epworth Sleepiness Scale (ESS) and other questions about sleep and sleep disorders were not collected until nearly 2004, said by the Departments of Neurology and Sociomedical Sciences at Columbia University, New York.

A total of 2,092 participants answered questions relating to sleep disturbance for the study. These people had an average of 73 years and a high school graduation rate of 45%. The study comprised 18% whites, 20% blacks, and 60% Hispanics (2% were other ethnicities).

The investigators asked all of the participants the following questions:

• Do you know or have you been told that you snore at night?

• Do you know or have you been told that you choke or stop breathing when you are sleeping and, if yes, does it occur less than 5 nights per week (mild to moderate) or more than 5 nights per week (severe)?

Some degree of snoring was reported by 63%, whereas only 6% reported choking or stopping breathing during sleep.

Each participant also answered eight questions on a modified version of the ESS, which asked about daytime sleepiness to document sleep disturbance. The scale asks, “How often would you say that you doze while you’re sitting and reading; watching television; sitting inactive in a public place; as a passenger in a car, train, or bus; sitting or talking to someone, sitting quietly after lunch; as a driver in a car; or in any other situation where you doze.

Overall, 44% reported no dozing, 47% reported some dozing and 9% reported a significant level of dozing, defined on the ESS as a score of 10 or higher.

During a mean follow-up period of 2.3 years, the participants have suffered 40 strokes (31 of which were ischemic), 123 vascular events (stroke, myocardial infarction, or vascular death), and 156 total deaths.

There was no significant association between snoring (at any level of severity) and vascular events, but there was a significant dose-response relationship between a person’s level of sleepiness and their risk for stroke. Patients who reported some dozing had more than twice the risk of both ischemic stroke and all types of stroke, compared with people who reported no dozing, whereas those with “significant dozing” had a more than threefold higher risk of ischemic stroke and a more than fourfold higher risk of all types of stroke. These analyses were adjusted for age, gender, race/ethnicity, education, systolic blood pressure, diabetes, physical activity, obesity, and coronary artery disease.

Compared with participants who reported no dozing, the risk of having a vascular event was 40% higher for those who reported some dozing and was more than two times higher for those who reported significant dozing.

The study is limited by an uncertainty of what truly is being measured. Is it measuring sleep apnea, disturbance, or deprivation, or is there an underlying process that is contributing to daytime sleepiness?

We need to validate all of this with gold-standard sleep studies, although the Epworth (Sleepiness) Scale has been tested and has been well validated.

The elevated risk in the highly prevalent ‘some dozing’ group (shows that) the impact of this novel risk factor may be quite important in further studies.

Prior to the current study, most studies in this area of research have focused on the associations between sleep (apnea and deprivation) and the development of vascular risk factors such as hypertension, obesity and diabetes, as well as the relationship between sleep apnea and stroke.