Although the Centers for Disease Control and Prevention (CDC) recommend that adults ages 18 to 60 years should get at least 7 hours of sleep each night, only 65.2% of adults surveyed in United States in 2014 reported that they consistently meet this standard.1 These results are concerning, as inadequate sleep has been associated with a range of adverse health effects including diabetes, high blood pressure, mental distress, and an increased risk for accidents related to impaired cognitive performance.1

In addition, there is accumulating evidence supporting the notion that sleep duration may have an effect on cardiovascular health, with several studies linking both insufficient and excessive sleep duration to an increased risk for cardiovascular disease (CVD). A meta-analysis of 74 studies (n=3,340,684) by Chun Shing Kwok, MBBS, MSc, BSc, MRCP(UK), clinical lecturer in cardiology at Keele University in Staffordshire, United Kingdom, and colleagues, indicated that self-reported sleep duration exceeding 8 hours per night—but not sleep duration <7 hours—was associated with an increased risk for all-cause mortality and cardiovascular events.2 An association was also observed between subjective poor sleep quality and an increased risk for coronary heart disease.

In a cross-sectional study published in the American Journal of Cardiology, which Krittanawong, et al conducted to examine the connection between sleep duration and the prevalence of a set of measures of cardiovascular health,  the researchers analyzed self-reported data from 32,152 participants in the National Health and Nutrition Examination Survey (NHANES).3 After adjusting for age, sex, physical activity levels, depression, and other potentially confounding variables, short sleep duration (ie, <7 hours per night) was found to be associated with a greater prevalence of previous heart failure (odds ratio [OR], 1.65; 95% CI, 1.40-1.95), stroke (OR, 1.45; 95% CI, 1.23-1.70), diabetes mellitus (OR, 1.35; 95% CI, 1.23-1.49), and hyperlipidemia (OR, 1.12; 95% CI, 1.04-1.22).3 In addition, longer sleep duration (ie, >9 hours per night) was found to be associated with a greater prevalence of previous stroke (OR, 1.81; 95% CI, 1.37-2.34) and heart failure (OR, 1.47; 95% CI, 1.08-1.97).

Although more research is needed to elucidate underlying mechanisms, the authors of this study hypothesized that the increased cardiovascular risks associated with short and long sleep durations may be attributed to factors such as metabolic impairment and lifestyle behaviors including poor dietary and exercise patterns. They also noted that there is no recommendation regarding sleep duration in the current American College of Cardiology/American Heart Association guidelines for CVD prevention.4 “With further prospective studies, national guidelines may consider advocating for optimal sleep duration to reduce cardiovascular health risks,” they noted.3 


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In an article published in the American Journal of Cardiology, Saurab Aggarwal, MD, cardiologist and director of echocardiography at Unity Point Health in Des Moines, Iowa, and colleagues described similar results in their 2013 cross-sectional study using data from a smaller NHANES sample.5 In their study, short sleep duration (ie, <6 hours) was associated with an elevated prevalence of self-reported history of stroke (OR, 2.01; 95% CI, 1.43-2.81) and heart failure (OR, 1.67; 95% CI, 1.55-2.41), as well as myocardial infarction, which was not examined in the more recent study. Long sleep duration (ie, >8 hours) was associated with an increased prevalence of coronary artery disease (OR, 1.19; 95% CI, 1.07-3.42).5

According to the authors of this 2013 study, the lack of adjustment for self-reported history of sleep apnea represents one limitation of the study by Krittanawong, et al. Sleep apnea may be associated with longer sleep duration and has been linked to greater CVD risk across various studies. “Therefore, it would be important to know whether the results hold when adjusted for history of sleep apnea,” the authors noted. “This— along with difference in sleep duration categories—may explain some differences noted between our previous analysis and current results reported by the authors.”3

We further discussed these study results with Drs Kwok and Aggarwal.

What do your findings suggest about associations between sleep duration and CVD?

Dr Kwok: The recommended sleep duration is 7 to 8 hours each night for people ages ≥65 years, and the top finding from our study was that sleeping beyond 8 hours was associated with greater adverse outcomes compared with sleeping less than 7 hours.

Dr Aggarwal: There appears to be a J-shaped curve between sleep duration and CVD where both short and long sleep durations cause excess CVD. The ideal duration appears to be between 7 and 9 hours. 

What are the relevant clinical implications for CVD prevention and treatment?

Dr Kwok: Patients who sleep beyond the recommended hours should be assessed for cardiovascular risk factors or underlying illnesses such as obstructive sleep apnea, anemia, heart failure, or hypothyroidism that may increase their cardiovascular risk. Perhaps clinicians should consider abnormal sleep in terms of below or above recommended durations, and sleep quality as a symptom which may represent early disease before a formal diagnosis.

Dr Aggarwal: Sleep patterns should be evaluated in every patient, as this is too often overlooked. Sleep has inherent effects on the pathophysiology of many disorders by regulating body metabolism. Sleep duration, pattern, and sleep disorders should be an integral part of any diagnostic workup, especially a CVD workup. 

What are remaining research needs in this area?

Dr Kwok: Our study does not evaluate why we observed the increased risk for harm with prolonged compared with reduced duration of sleep [and there is a need for research identifying such mechanisms]. However, we can speculate as to reasons for these findings. Sleep is complex and influenced by many factors including work patterns, lifestyle, and responsibilities such as caregiving. People appear to have more control over having less sleep, but if an individual sleeps more than recommended, there may be underlying poor health that could be driving the need for more sleep.

Dr Aggarwal: The available data about sleep duration are all retrospective, limiting the derivation of causal relationship. Large prospective studies are needed to understand these associations. Randomized controlled trials of sleep interventions are needed to inform optimal recommendations for treatment and prevention. 

References

  1. Liu Y, Wheaton AG, Chapman DP, Cunningham TJ, Lu H, Croft JB. Prevalence of healthy sleep duration among adults–United States, 2014. MMWR Morb Mortal Wkly Rep. 2016;65(6):137-141.
  2. Kwok CS, Kontopantelis E, Kuligowski G, et al. Self-Reported sleep duration and quality and cardiovascular disease and mortality: a dose-response meta-analysis. J Am Heart Assoc. 2018;7(15):e008552.
  3. Krittanawong C, Kumar A, Wang Z, et al. Sleep duration and cardiovascular health in a representative community population (from NHANES, 2005 to 2016). Am J Cardiol. 2020;127:149-155.
  4. Arnett DK, Blumenthal RS, Albert MA, et al. 2019 ACC/AHA guideline on the primary prevention of cardiovascular disease: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. Circulation. 2019;140(11):e596-e646.
  5. Aggarwal S, Loomba RS, Arora RR, Molnar J. Associations between sleep duration and prevalence of cardiovascular events. Clin Cardiol. 2013;36(11):671-676.