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DAYTIME NAPS MAY BE A RISK FACTOR FOR A STROKE

ARTICLE IN BRIEF

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People who dozed off most often had a greater than four-fold risk of having a stroke than people who stayed awake all day long.

NEW ORLEANS—Older people who tend to doze off during the daytime may be revealing signs that they are at risk of suffering a stroke.

“Sleep is an important modulator of cardiovascular function,” said Bernadette Boden-Albala, MPH, DrPH, assistant professor of neurology at Columbia University in New York City. “Some studies have suggested that poor quality and diminished quantity of sleep may be independently linked to cardiovascular events, although prospective studies are few and limited.”

In a new study, Dr. Boden-Albala and colleagues found that sleep disturbances marked by inappropriate dozing episodes seems to be linked to a marked increase in the risk of stroke. People who dozed off most often had a greater than four-fold risk of having a stroke than people who stayed awake all day long. The findings were based on an analysis of data involving volunteers in the Northern Manhattan Study, an ongoing study of risk factors for stroke among residents of the Washington Heights neighborhood in New York City.

Participants were asked to report whether they knew or had been told that they snore at night, choke, or stop breathing, and to assess the frequency of events (none, mild or moderate, or severe). And they were assessed for daytime sleepiness using the Epworth Sleep Scale (See “Questions Asked: The Epworth Sleep Scale”).

“The hazard ratio for stroke was 2.6 for all strokes and 2.1 for ischemic stroke among those who reported some dozing,” Dr. Boden-Albala said here in February at the American Stroke Association International Stroke Conference. “The hazard ratio for stroke was 4.5 for all strokes and 3.4 for ischemic strokes among individuals with self-reported significant dozing.”

“We have known for some time that sleep apnea is linked to stroke and other cardiovascular diseases, and dozing in the daytime can be caused by sleep apnea,” said Mark Alberts, MD, director of the Stroke Program at Northwestern Memorial Hospital, in Chicago. “However, because this study is based on self-reports we can't be sure that dozing in this age group is caused by sleep apnea or some other factor.”

Dr. Alberts added:“If a person has excessive daytime sleepiness, we recommend that the person should undergo a sleep evaluation.” But, he added, just because a person dozes in the daytime, he or she shouldn't assume a stroke is imminent. He said a proper evaluation could determine if the person is suffering from sleep apnea or has other form of sleeping problem.

“Cardiovascular disease and dozing may be part of the clinical picture of people with sleep apnea.”

STUDY PROTOCOLS

Dr. Boden-Albala and colleagues enrolled 3,298 people, age 55 or older, in a prospective trial. All were given a neurological exam and assessed for vascular risk profile, blood pressure, anthropometrics, and fasting blood levels. They were also given the Epworth Sleepiness Scale to assess daytime sleepiness, and were asked to report their snoring and choking episodes; all had annual follow-ups between 1993 and 2006.

During the 2.5-year mean follow-up, there were 40 strokes, 123 vascular events, and 156 deaths. About 63 percent (1,318) of participants knew or were told they snore; 6 percent (126) were told they choke or stop breathing during sleep; and 2 percent (42) had been diagnosed with sleep apnea. In the Epworth categories, 44 percent (921) reported no dozing; 47 percent (983) reported some dozing; 9 percent (188) reported significant dozing.

“While there were no significant differences among the groups in overall deaths, the participants who experienced mild sleepiness had a 1.4 hazard ratio for the risk of having ischemic vascular events compared with those who did not report daytime sleepiness,” Dr. Boden-Albala said. “Those who reported significant daytime sleepiness had a 2.6 hazard ratio for experiencing vascular events.”

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DR. MARK ALBERTS: “We have known for some time that sleep apnea is linked to stroke and other cardiovascular diseases, and dozing in the daytime can be caused by sleep apnea. However, because this study is based on self-reports we cant be sure that dozing in this age group is caused by sleep apnea or some other factor.”

Dr. Boden-Albala suggested that the study has limitations, a major one being that it was not certain whether doctors were actually studying sleep apnea or disturbed sleep. She admitted that self-reported episodes of snoring can be inaccurate. The results need to be validated with “gold-standard sleep studies,” she said.

“Findings from this prospective cohort study demonstrate that daytime sleepiness, as measured by the Epworth Sleepiness Scale, is an independent risk factor for stroke as well as for all vascular events,” Dr. Boden-Albala said. “Further, the increased risk in the highly prevalent ‘some dozing’ group suggests that the effect of this novel risk factor may be important, and further studies of the relationship between sleep and stroke are warranted.”

QUESTIONS ASKED: THE EPWORTH SLEEPINESS SCALE

The Epworth Sleepiness Scale asks participants to score — on a 0–3 scale

  • how often they doze while sitting:
  • and reading.
  • inactive in a public place.
  • as a passenger in a car, train, or bus.
  • and talking to someone.
  • quietly after lunch.
  • as a driver in a car stopped for traffic.

The score is obtained by adding the numbers: 0–9 indicates an average score, normal population; 10–24 indicates a sleep specialist is recommended for advice.