“Obesity, heart disease, and diabetes are major diseases facing our population. As our knowledge about these conditions increases, we are learning that many aspects of our health, especially when it comes to our hearts, are intertwined with how we sleep,” says Michael Grandner, PhD, Instructor in Psychiatry and member of the Center for Sleep and Circadian Neurobiology at Penn. “The connections are complex and we are just starting to scratch the surface.”
In recent years, sleep researchers have been able to show that too little or too much sleep can have some bad effects on the heart. A study presented at the 2012 American College of Cardiology meeting found that getting less than 6 hours of sleep each night was associated with an increased likelihood of having congestive heart failure and stroke, while sleeping more than 8 hours was associated 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 of the week was associated with obesity, diabetes, heart attack, coronary artery disease, and stroke.
In addition to these relatively new findings, Grandner and colleagues at Penn Medicine have made two new important discoveries that are helping to unravel the complicated relationship between sleep and heart health, specifically in the area of sleep duration.
In the first study, published in the December 2012 edition of the journal Sleep Medicine, Grandner and his colleagues investigated the relationship between sleep insufficiency and sleep duration, particularly regarding adverse cardiometabolic health outcomes, such as diabetes, hypertension, and high cholesterol. To analyze this connection, they reviewed data from the 2009 Behavioral Risk Factor Surveillance System (BRFSS), the world’s largest, on-going telephone health survey system that tracks health conditions and risk behaviors in the United States. After looking at the data from over 30,000 participants they discovered that that both sleep duration and insufficiency are related to negative cardiometabolic health outcomes.
“What was particularly interesting about this study was that we looked at sleep two ways,” says Grandner. “First, we looked at how much people were getting (without consideration of whether they felt that was enough), and then we looked at whether people felt they weren’t getting enough sleep (without consideration of how much they were getting). Both of those ways of looking at sleep seemed to tell a similar story. Then, we took it to the next level by seeing which one drove the effects of the other. For most of the outcomes, sleep duration explained most of the effects of insufficiency, but insufficiency did seem to drive the relationship with high cholesterol. Both contributed to high blood pressure. So that tells us that it’s not just about how much you are sleeping and it’s not just about how you feel your sleep needs are being met.”
In the second study, online now pending print publication in the May issue of the journal SLEEP, Grandner’s research team examined the association between sleep duration and C-reactive protein (CRP), a systemic marker of chronic, low-grade inflammation in the body. Previous research has shown that elevated levels of CRP are associated with a threefold increase in the risk of heart attack. In addition to CRP’s role in cardiac risk, sleep scientists have also found that it might be partially regulated by sleep, with lab studies showing elevated CRP resulting from acute sleep deprivation. But population-level studies have not been able to tease apart this relationship in the general population. So Grandner wanted to find out exactly how CRP is related to sleep duration in the American population. For this study, they turned to the 2007-2008 National Health and Nutrition Examination Survey (NHANES) sponsored by the CDC. NHANES includes the demographic, socioeconomic, dietary, and health status of the U.S., using surveys, blood tests, and in-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 and sleep duration, meaning people who experienced very short or very long sleep duration were more likely to show elevated CRP levels. When they drilled down deeper, they found that this U-shape is most prominent at the extremes of sleep duration (very short or very long sleep), and it is different for men and women. It also differs between ethnic and racial groups. This may explain why studies that included smaller or more restricted samples failed to find this relationship.
“This study revealed that extremes of sleep duration increase pro-inflammatory risk,” says Grandner. “From this study, we believe that differences in CRP should be considered in future research on sleep-related disparities influencing cardiometabolic disease risk.”
In ongoing research, Dr. Grandner and colleagues at Penn are involved 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 is a regional study of the relationship between habitual sleep duration and health risks. The study aims to take a broader view of health and sleep and examine a number of factors that may increase risk of obesity, heart disease, diabetes, and other important, related diseases. The SHADES study is another regional study that involves both a random survey of local residents and an in-depth study using state-of-the-art sleep and environmental measurements to measure how, why, and when we sleep the way that we do in the real world, and how this may 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 and the more we study sleep and health, the more we find out how important it is to every function of our bodies and minds.”