US researchers found that poor sleep quality, that is not getting a good night’s sleep or not enough sleep, is linked to higher levels of inflammation, a known risk factor for heart disease and stroke.
These were the findings of a community study that Dr Alanna Morris, a cardiology fellow at Emory University School of Medicine in Atlanta, Georgia, presented on Sunday at the American Heart Association (AHA) 2010 Scientific Sessions in Chicago.
The study is part of the Emory-Morehouse Partnership to Reduce CV Disparities (META-Health), a joint initiative between Emory and Morehouse School of Medicine, also in Atlanta. An abstract of the study is published in the 23 November issue of Circulation, an AHA journal.
Morris said other studies have already shown a link between acute lack of sleep and inflammation markers and changes in blood vessels, but there is not enough research information on the physiological effects of chronic lack of sleep.
“Most of the studies looking at the body’s response to lack of sleep have looked at subjects who have been acutely sleep deprived for more than 24 hours in experimental sleep laboratories,” said Morris.
“Nothing of this sort has been investigated in epidemiologic studies,” she added.
Morris and colleagues examined data on 525 middle-aged participants of the META-Health study who had filled in the Pittsburgh Sleep Quality Index (PSQI) questionnaire. 47 per cent of the participants were African American, and 61 per cent were female.
The PSQI asked the participants detailed questions about sleep duration and sleep quality.
The researchers defined poor sleep as a total PSQI score of six or more, based on the median score. They also analyzed data according to hours of sleep, in three groups: less than 6 hours per night, between 6 and 8.9, and 9 hours or more.
The participants’ levels of three inflammatory markers: fibrinogen, IL-6 and C-reactive protein (CRP), were also examined as continuous values.
C-reactive protein (CRP) is often used as a marker of inflammation and heart disease risk.
According to the AHA and the US Centers for Disease Control and Prevention (CDC), people whose CRP is above 3 mg per litre, that is the upper third of the US population, have around twice the risk of a heart attack compared to those with lower levels.
After adjusting the results to take into account potential demographic (age, gender, race) and health (smoking, diabetes, blood pressure, glucose, waist size, blood fat levels) confounders, the researchers found that:
- Participants with poor sleep quality had significantly higher levels of fibrinogen, IL-6, and CRP than participants with good sleep quality.
- Levels of the three inflammatory markers also differed across the three categories of sleep duration.
- Sleep duration of 6 to 8.9 hours was linked to significantly lower levels of mean fibrinogen, median IL-6 and CRP compared to sleep duration of under 6 hours.
- Comparisons between 6 to 8.9 and nine hours or more of sleep duration did not show any statistically significant effects.
The researchers concluded that “Poor sleep quality, and short sleep durations are associated with higher levels of inflammation.”
They suggested that improving sleep quality and duration may be an appropriate therapeutic target for reducing cardiovascular disease risks.
Morris said that although the increased levels of C-reactive protein seen in those participants who got little sleep were within the range that health authorities would describe as low to intermediate cardiovascular disease risk, this study looked at community-based participants, as opposed to hospital patients with known cardiovascular disease, “so they have overall lower risk and lower C-reactive protein levels than many of the high risk populations in other studies”.
Inflammation could be a route through which poor sleep quality increases the risk of heart disease and stroke, said Morris.
But she pointed out that it is still not clear whether short sleep duration contributes directly to cardiovascular mortality or whether it is a mediating factor.
Other studies have shown that having between 7 and 8 hours sleep a night is linked to living longer, and sleeping a lot less or a lot more than that is linked to shorter lifespan. Short and long sleep durations have also been associated with high blood pressure, obesity, diabetes and stress, all of which are known risk factors for heart disease and stroke, although in this study there was no significant result for longer sleep duration.
Morris and colleagues are also reporting to the conference the results of a separate study that looked at the difference between men and women in terms of links between sleep quality and artery hardening or stiffness, where lack of flexibility in the vessel wall causes high blood pressure and makes the heart work harder.
Those results showed that while poor sleep was linked to higher blood pressure in both men and women, the link between poor sleep quality and arterial stiffness was only significant for men.