ORLANDO – Hypertensive persons who sleep 5 hours or less per night have a significantly higher all-cause mortality rate than those who get more shut-eye, according to an analysis from the Penn State Adult Cohort Study.
“We found that the odds of all-cause mortality associated with hypertension increased in a dose-response manner as a function of the degree of objective short sleep duration, even after adjusting for a multitude of factors,” Julio Fernandez-Mendoza, Ph.D., reported at the American Heart Association scientific sessions.
©Bruce Jancin/Frontline Medical News
Dr. Julio Fernandez-Mendoza
The Penn State Adult Cohort consists of a random, general population sample of 1,741 men and women who enrolled in the study back in the 1990s, at a mean age of 48.7 years. As part of their comprehensive evaluation they were studied in the overnight sleep laboratory. The cohort has been followed for 15.5 years, during which 20% of subjects died.
As expected, hypertension was associated with increased risk of all-cause mortality in the Penn State Adult Cohort. But Dr. Fernandez-Mendoza and coinvestigators further dissected this association by incorporating the subjects’ objective sleep lab data, something that hadn’t been done in other studies. They found that while as a group the roughly 35% of study participants with hypertension had an adjusted 2.54-fold increased risk of all-cause mortality, compared with normotensive subjects, those who slept 6 or more hours at night – placing them at or above the 50th percentile for sleep duration – had a 1.75-fold increased risk, which just barely reached statistical significance.
In contrast, those who slept 5-6 hours per night were at 2.36-fold increased risk of all-cause mortality, while hypertensives in the bottom quartile for sleep duration with 5 hours or less of sleep had an even more robust 4.04-fold increased risk. All risk figures were determined in a multivariate logistic regression analysis extensively adjusted for age, gender, race, diabetes, obesity, smoking, depression, insomnia, sleep apnea, and history of heart disease or stroke.
This finding of an inverse association between sleep duration and all-cause mortality was consistent with the investigators’ study hypothesis that short sleep duration in hypertensive patients may be a marker of the severity of autonomic dysfunction. After all, it is known that the autonomic nervous system not only controls cardiovascular function, it also regulates sleep, explained Dr. Fernandez-Mendoza, a behavioral psychologist at Pennsylvania State University in Hershey.
Other possible explanations for the findings are that short sleep duration in hypertensive patients might be genetically driven or behaviorally induced, but he considers these less plausible.
In an interview, Dr. Fernandez-Mendoza said he and his coinvestigators have found the same relationship between short sleep duration and increased all-cause mortality in Penn State Adult Cohort members with diabetes or dyslipidemia, although he didn’t present those data at the AHA meeting.
If indeed short sleep duration is a marker of autonomic dysfunction, it would have important clinical implications: “Objective sleep duration may allow for refinement of estimates of mortality risk. I predict that someday cardiovascular risk calculators will incorporate sleep duration,” he said.
The Penn State Adult Cohort findings bring a measure of clarity to what has been a somewhat cloudy area, Dr. Fernandez-Mendoza said. Most prior epidemiologic studies of sleep’s impact on health have relied upon self-reported sleep duration, which is considerably less reliable than objectively measured sleep lab data. And many studies have looked at sleep duration as an isolated variable in relation to morbidity and mortality risk. This, he said, has contributed to public misunderstanding.
“We have people coming into the sleep lab thinking, ‘If I don’t get 7 hours of sleep I’m going to die,’ ” according to the sleep scientist. “But the paradigm we’ve developed, tied to what we know about autonomic control, is that the cardiovascular system and the sleep system are connected to each other. It doesn’t mean that short sleep kills you, it’s that the combination of the traditional cardiometabolic risk factors and short sleep increases risk of morbidity and mortality.”
Dr. Fernandez-Mendoza’s study was funded by an AHA Scientist Development Grant. He reported having no financial conflicts of interest.