by Craig Weatherby
There's no question that people need their sleep, with studies linking a lack of shut-eye to everything from weakened immunity and cognitive deficits to weight gain.
Americans average 8.6 hours of sleep a night, but parents only get about 7.6 hours. Since these figures are averages, it means that many people get less sleep.
And it now looks as though chronic sleep shortage could put you on a path toward cardiovascular disease.
A research team from the University of Chicago reports that getting one extra hour of sleep may reduce your risk of hardened arteries.
Hardened arteries—which doctors call “coronary artery calcification”—constitutes an early stage of cardiovascular disease.
And the new findings from Chicago suggest that getting more sleep could reduce your risk of cardiovascular disease as much as lowering your systolic blood pressure by 17 mm Hg.
Cardiovascular disease risk doubles for each added blood pressure increment of 20 mmHg. Thus, getting an extra hour of sleep could cut your risk of cardiovascular disease very dramatically.
Recent research results indicate that sleeping longer is linked to improvements in major risk factors for artery calcification, including blood sugar regulation, blood pressure, and body mass index.
Results point to benefits of serious sleep
The study involved 495 healthy volunteers in their 40s, about 12 percent of whom developed coronary artery calcification during five years of follow-up (King CR et al. 2008).
Alarmingly, calcified arteries were found in more than twice as many (27 percent) of those who slept less than five hours a night.
In contrast, only 11 percent of those who slept five to seven hours showed artery calcification, and calcification appeared in only six percent of those who averaged more than seven hours of sleep.
The benefits of sleep appeared to be greater for women, and did not vary according to ethnicity.
"The consistency and the magnitude of the difference came as a surprise“, said study director Diane Lauderdale, Ph.D. “It's also something of a mystery. We can only speculate about why those with shorter average sleep duration were more likely to develop calcification of the coronary arteries” (UCMC 2008).
Recent studies have suggested that chronic partial sleep deprivation may be a risk factor for an array of common medical problems, including weight gain, diabetes, and hypertension.
One study found that both long and short self-reported sleep durations were independently associated with a modestly increased risk of adverse coronary events (e.g. heart attacks and arrhythmias).
This is the first study to link sleep duration to a pre-clinical marker for heart disease.
Study authors probed arteries to find link to sleep
The research focused on participants in the Coronary Artery Risk Development in Young Adults (CARDIA) study, which is an ongoing project designed to assess the long-term impact of various factors on the development of coronary artery disease.
Participants underwent two computed tomography (CT) scans, designed to assess the buildup of calcium within the arteries that deliver blood to the heart muscle, five years apart.
They also filled out sleep questionnaires, kept a log of their hours in bed, and participated in six nights of sleep studies with a technique called wrist actigraphy that uses a motion sensor—worn like a watch—to estimate actual sleep duration.
This approach provides the most accurate measure of routine sleep behavior without subjecting the volunteers to the unfamiliarity of multiple sensors that determine sleep by monitoring brain activity.
In a previous study, professor Lauderdale and her colleagues used wrist actigraphy and nightly logs to study, on average, how long people spent in bed (7.5 hours), how long it took them to fall asleep (22 minutes), how long they slept (6.1 hours), and their total "sleep efficiency"—the time asleep divided by the time spent trying to sleep in bed (81 percent).
This time they looked at the connections between sleep duration and coronary artery calcification. They found more than they anticipated.
Previous studies have correlated decreased sleep times with established risk factors for calcification, including high blood pressure, excess weight, and poor glucose regulation.
But in this study, as the authors wrote, “…after adjusting for age, sex, race, education, smoking, and apnea risk, longer measured sleep duration was associated with reduced calcification incidence.”
The authors suggest three possible ways that shorter sleep could connect to calcification.
- There may be some factor not yet identified that can both reduce sleep duration and increase calcification.
- Although blood pressure measured during examinations did not seem to explain the association, blood pressure generally declines during sleep, so the 24-hour average blood pressure of those who sleep less may be higher, and that could lead to calcification.
- Stress or a stress hormone like cortisol, which has been tied to decreased sleep and increased calcification, may play a role (Cortisol measurements were not available for all study participants).
- King CR, Knutson KL, Rathouz PJ, Sidney S, Liu K, Lauderdale DS. Short Sleep Duration and Incident Coronary Artery Calcification. JAMA. 2008 Dec 24;300(24):2859-2866.
- University of Chicago Medical Center (UCMC). Skipping sleep may signal problems for coronary arteries. December 23, 2008. Accessed online December 27, 2008 at http://news.uchicago.edu/news.php?asset_id=1515