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Penn Medicine Researchers Take a Closer Look at Sleep and Heart Health

IheartsleepingWhen most people think about ways to improve their hearthealth, they consider eating a healthier diet, getting some additionalexercise, and possibly sipping a glass of red wine each night. But few peoplereally consider the complex role that sleep – yes, sleep – plays in theiroverall cardiovascular fitness.

Fresh off our HeartMonth blog series and straight into National Sleep Awareness Week, we’re takinga look at the major role that sleep plays in heart health.

“Obesity, heart disease, and diabetes are major diseasesfacing our population. As our knowledge about these conditions increases, weare learning that many aspects of our health, especially when it comes to ourhearts, are intertwined with how we sleep,” says Michael Grandner, PhD,Instructor in Psychiatry and member of the Center for Sleep and CircadianNeurobiology at Penn. “The connectionsare complex and we are just starting to scratch the surface.”

In recent years, sleep researchers have been able to showthat too little or too much sleep can have some bad effects on the heart. Astudy presented at the 2012 American College of Cardiologymeeting found that getting less than 6 hours of sleep each night was associatedwith an increased likelihood of having congestive heart failure and stroke,while sleeping more than 8 hours wasassociated with greater odds of having coronary artery disease and angina.Other research by Dr. Grandner and colleagues at Penn has shown that sleep disturbance on at least three nights out ofthe week was associated with obesity, diabetes, heart attack, coronary arterydisease, and stroke. 

In addition to these relatively new findings, Grandnerand colleagues at Penn Medicine have made two new important discoveries thatare helping to unravel the complicated relationship between sleep and hearthealth, specifically in the area of sleep duration.

In the first study, published in the December 2012 editionof the journal Sleep Medicine, Grandner and his colleagues investigatedthe relationship between sleep insufficiency and sleep duration, particularlyregarding adverse cardiometabolic health outcomes, such as diabetes,hypertension, and high cholesterol. To analyze this connection, they revieweddata from the 2009 Behavioral Risk Factor Surveillance System (BRFSS), theworld’s largest, on-going telephone health survey system that tracks healthconditions and risk behaviors in the United States. After looking at the datafrom over 30,000 participants they discovered that that both sleep durationand insufficiency are related to negative cardiometabolic health outcomes.

“What was particularly interesting about this study was thatwe looked at sleep two ways,” says Grandner. “First, we looked at how muchpeople were getting (without consideration of whether they felt that wasenough), and then we looked at whether people felt they weren’t getting enoughsleep (without consideration of how much they were getting). Both of those waysof looking at sleep seemed to tell a similar story. Then, we took it to thenext level by seeing which one drove the effects of the other. For most of theoutcomes, sleep duration explained most of the effects of insufficiency, butinsufficiency did seem to drive the relationship with high cholesterol. Bothcontributed to high blood pressure. So that tells us that it’s not just abouthow much you are sleeping and it’s not just about how you feel your sleep needs arebeing met.”

In the second study, online now pending print publication inthe May issue of the journal SLEEP, Grandner’s research teamexamined the association between sleep duration and C-reactive protein (CRP), asystemic marker of chronic, low-grade inflammation in the body. Previousresearch has shown that elevated levels of CRP are associated with athreefold increase in the risk of heart attack. In addition to CRP’s role incardiac risk, sleep scientists have also found that it might be partiallyregulated by sleep, with lab studies showing elevated CRP resulting from acutesleep deprivation. But population-level studies have not been able to teaseapart this relationship in the general population. So Grandner wanted tofind out exactly how CRP is related to sleep duration in the Americanpopulation. For this study, they turned to the 2007-2008 National Health andNutrition Examination Survey (NHANES) sponsored by the CDC. NHANES includes the demographic, socioeconomic,dietary, and health status of the U.S., using surveys, blood tests, andin-person exams. The sample for the survey is selected to represent the U.S.population of all ages and demographics.

Overall, they found a U-shaped relationship between CRP andsleep duration, meaning people who experienced very short or very long sleepduration were more likely to show elevated CRP levels.  When they drilled down deeper, they foundthat this U-shape is most prominent at the extremes of sleep duration (veryshort or very long sleep), and it is different for men and women. It also differsbetween ethnic and racial groups. This may explain why studies that includedsmaller or more restricted samples failed to find this relationship.

“This study revealed that extremes of sleep durationincrease pro-inflammatory risk,” says Grandner. “From this study, we believethat differences in CRP should be considered in future research onsleep-related disparities influencing cardiometabolic disease risk.”

In ongoing research, Dr. Grandner and colleagues at Penn areinvolved in the Cardiometabolic Health And Relationships To Sleep (CHARTS)study and the Sleep and Healthy Activity, Diet, Environment and Socialization(SHADES) study, which are both sponsored by the National Institutes of Health. CHARTS isa regional study of the relationship between habitual sleep duration and healthrisks. The study aims to take a broader view of health and sleep and examine anumber of factors that may increase risk of obesity, heart disease, diabetes,and other important, related diseases. The SHADES study is another regionalstudy that involves both a random survey of local residents and an in-depthstudy using state-of-the-art sleep and environmental measurements to measurehow, why, and when we sleep the way that we do in the real world, and how thismay impact other aspects of health.

Grandner says "When we think about our health – including heart health –we should be thinking about our sleep. Sleep is an essential part of life andthe more we study sleep and health, the more we find out how important it is toevery function of our bodies and minds.”

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