Excessive daytime drowsiness in older adults may predict a significantly increased risk of stroke, said researchers reporting data on Thursday at the International Stroke Conference in New Orleans.
Most people have, from time to time, unintentionally dozed off on the couch watching television or reading a book or even stopped in traffic while driving. But persistent drowsiness during the day usually signals a chronic sleep deficit, and bigger problems. The new study found that people who suffered from "significant dozing" — those who almost always fell asleep involuntarily during the day — were 4.5 times more likely to have a stroke than people in the "no dozing" group. The association between sleepiness and stroke was dose-dependent: the sleepier the person, the higher the risk of stroke. People in the "some dozing" group, who sometimes, but not always, fell asleep while watching TV or while sitting quietly after lunch, had a 2.6 higher risk of stroke than their more alert peers.
The study tracked 2,153 participants, average age 73, as part of the ongoing Northern Manhattan Study on stroke, led by Columbia University researchers. The participants were tracked for about two years — none had had a stroke when the study began — and their daytime drowsiness was assessed using a standard sleepiness scale. Of the group, 44% were never-dozers, 47% were sometimes-dozers and 9% were always-dozers. During the follow-up period, the group had 40 strokes and 127 other vascular events, such as heart attack. The data showed not only an increase in stroke risk with excessive daytime sleepiness, but also an increased risk of heart attack and vascular death: compared with well-rested people, moderately sleepy people had a 1.6 times higher risk; for severely sleepy people, the risk was 2.6 times greater.
Past studies have examined the link between sleep and stroke, but that research has focused mainly on people with sleep apnea, a disorder that causes interruptions in breathing or shallow breaths during sleep. In one study involving patients with severe sleep apnea (five or more episodes of apnea per hour), researchers found it was "significantly related to a two-fold increased risk of a stroke," says Bernadette Boden-Albala, lead author of the current study and assistant professor of neurology at Columbia University's College of Physicians and Surgeons.
"That study involved people who were already going to a clinic for sleep problems," says Boden-Albala, "[Our study is] an off-the-street, community-based, prospective cohort study. But one of the limitations of [our sleepiness scale] is that we're not really able to differentiate what type of sleep disturbances these people were having." While the scale indicates that people are sleepy during the day and therefore not resting well at night, it doesn't say why. In terms of stroke and other vascular risks, says Boden-Albala, "The question really is, Is it sleep apnea or is it the physiological consequence of not getting enough sleep?"
The preponderance of evidence would suggest that it's sleep apnea, which is known to cause severe blood-pressure variations. But, according to Boden-Albala, a growing body of research, including her own past work, suggests that sleep deprivation is linked to a variety of conditions, such as obesity, diabetes and hypertension, that may also contribute to vascular risk. "There's more to it than just sleep apnea but we need to figure out why," says Boden-Albala.
Only a small percentage of participants in Boden-Albala's study suffered from severe daytime sleepiness, but a full 47% reported moderate levels of uncontrollable dozing. "That's a public health problem," she says. "If you think you have a sleep problem, bring it up the next time you see your physician. And if you're falling asleep every single day watching television or when you try to read a book, that might be something serious."