Healthy sleep includes several components, including the number of hours of sleep per night, how long it takes to fall asleep, how well you sleep during the day and your self-rated sleep satisfaction. Addressing these different dimensions of sleep can help reduce cardiometabolic health risks and associated risk factors, according to a new scientific statement from the American Heart Association published in Circulation: Cardiovascular Quality and Outcomes.
How Sleep and Various Cardiometabolic Health Factors are Related
The new scientific statement “Multidimensional Sleep Health: Definitions and Implications for Cardiometabolic Health” describes various components of sleep health, including sleep duration, continuity, timing, satisfaction, regularity and diurnal pattern. The scientific statement also provides an overview of the latest findings on the relationship between sleep and various cardiometabolic health factors, including body fat, blood glucose, cholesterol and blood pressure, as well as the positive effects of healthy sleep on physical health and mental well-being.
“Most adults need 7 to 9 hours of sleep per night. Insufficient sleep increases the risk for cardiovascular disease, as well as cognitive decline, depression, obesity, hypertension, high blood sugar and high cholesterol,” said Scientific Working Group Chair Marie-Pierre St-Onge, Ph.D., C.C. S.H., C.C.A., FAHA, Associate Professor of Nutritional Medicine in the Department of Medicine and Director of the Center of Excellence for Sleep & Circadian Research, both at Columbia University Irving Medical Center in New York City. “However, there is growing evidence that sleep health is more than just the number of hours you sleep each night.”
The Components of Sleep
According to the scientific statement, a person’s sleep quality cannot be fully measured by a single aspect, nor can their body’s individual response. The less discussed and less researched components of sleep quality are relevant to the experience of sleep and contribute to overall physical and mental health and well-being. The components of sleep include:
- Sleep duration is the number of hours per night (or per 24-hour period) that a person sleeps. It can be estimated from a person’s self-reported sleep duration using questionnaires and diaries or assessed objectively using actigraphy (wearing a device that records movement) or polysomnography (using sensors to monitor brain activity, breathing, heart rate, blood oxygen levels and eye movements that measure sleep). Recent evidence from several studies suggests that sleeping less than 7 hours per night increases the risk of atrial fibrillation, cardiometabolic syndrome (a group of conditions that increase the likelihood of type 2 diabetes, heart disease or stroke) and blood pressure that does not drop as much during sleep (blood pressure should be lower at night/sleep than during the day/wakefulness and activity). Sleeping too much or sleeping more than 9 hours per night is also associated with an increased risk of cardiometabolic syndrome, hardening of the arteries, stroke or death from heart disease or stroke.
- Sleep continuity is the proportion of time spent sleeping. It is calculated using factors that reflect sleep disturbances, such as time taken to fall asleep, number of nocturnal awakenings, time spent awake after falling asleep, unplanned early waking (after falling asleep) and obstructive sleep apnea. Sleep continuity disorders are associated with a higher risk of atrial fibrillation, heart attack, high blood pressure or increased insulin resistance.
- Sleep timing refers to the time at which a person usually falls asleep within a 24-hour period. Studies that examine sleep timing look at how cardiometabolic risk changes with a person’s usual bedtime and whether they are more likely to sleep at night or during the day. High-quality research on sleep timing is limited, but data suggest that suboptimal sleep timing is likely associated with an increased risk of cardiovascular disease. A reported bedtime of midnight or later is associated with a higher risk of overweight or obesity, insulin resistance and elevated blood pressure compared to a bedtime before midnight.
- Sleep satisfaction is a person’s own perception of their sleep quality. A combined analysis of recent research shows that lower sleep satisfaction is associated with higher blood pressure, stiffer and less flexible arteries, coronary heart disease and an increase in blood pressure at night.
- Sleep regularity is the stability of a person’s sleep duration/timing over several days (for example, if the number of hours of sleep changes between weekdays and weekends, this is called “social jet lag”). Social jet lag is associated with a 20% higher risk of overweight or obesity, and daily variations in sleep patterns are associated with a higher risk of cardiovascular disease, hypertension, inflammation, obesity and blood pressure that does not drop at night. In large-scale studies, greater regularity in the sleep-wake cycle has been associated with a 22% to 57% lower risk of cardiovascular death. In a large UK Biobank study, an irregular sleep pattern was associated with a higher risk of type 2 diabetes, even in people who had adequate sleep, with the highest risk in those with insufficient sleep and very irregular sleep patterns.
- Sleep-related daytime functioning is a person’s ability to stay awake and alert during the day (including their level of sleepiness or drowsiness). It can be assessed by participants’ self-reports of how likely they are to fall asleep in certain situations (e.g. while watching TV or driving) or by assessing a person’s cognitive alertness (e.g. by testing reaction time to visual or auditory stimuli). Excessive daytime sleepiness is associated with cardiovascular disease, coronary heart disease, stroke and death from cardiovascular disease and all causes. Certain cardiovascular risks, including obesity, type 2 diabetes, depression, smoking and obstructive sleep apnea, were associated with a higher risk of daytime sleepiness, while weight loss appeared to reduce excessive daytime sleepiness.
- Sleep architecture refers to the stages of sleep that the body normally goes through during sleep and is assessed using electroencephalography (EEG) to measure electrical activity in the brain. Sleep is divided into two categories: Non-Rapid Eye Movement (N-REM) sleep, which includes the stages of light and deep sleep, and Rapid Eye Movement (REM) sleep, the deepest stage of sleep. Sleep continuity disorders can affect the sleep stages in different ways. An analysis of combined studies found that disruption of NREM sleep, also known as slow-wave sleep, led to higher insulin resistance than uninterrupted sleep.
Differences in Sleep Health
The statement also looks at differences in sleep health among people affected by negative social determinants of health. A recent review of more than 300 studies found a consistent association between lower socioeconomic status and suboptimal sleep health. Social and environmental factors, including home and neighborhood characteristics such as light, air and noise pollution and safety, also contribute to differences in one or more components of sleep health. Compared to non-Hispanic whites, members of historically underrepresented ethnic groups sleep less and are more likely to suffer from poorer sleep continuity, less satisfaction with sleep, later bedtimes, more irregular sleep, higher daytime sleepiness, and more frequent occurrence of sleep disorders. These differences can be observed across the lifespan and persist over time, with black adults having the poorest sleep health of any population group.
“It’s important to realize that everyone has different sleep habits and that these differences may contribute to other health disparities,” St-Onge said. Including different sleep components in conversations with patients provides important information that can help healthcare professionals improve care. Questions such as “How long does it usually take you to fall asleep?”, “How often do you wake up at night?” and “How often do you feel exhausted during the day?” give patients the opportunity to express their concerns about their sleep habits and sleep quality. Documenting sleep details in patients’ medical records helps the healthcare team learn about patients’ sleep health and may lead to a more in-depth examination or screening. This information is also helpful in assessing the extent to which a patient’s health condition and prescribed medications are affecting sleep health and need to be adjusted or changed.
Awareness of the importance of sleep is growing, but more research is needed on the various dimensions of sleep health so that doctors can support their patients with interventions to promote healthy sleep and improve their health. While there are numerous smartwatches and other personal devices that can be used to track sleep duration per night, progress is needed in assessing other dimensions of sleep. Using data from self-reported and objective measurements can help ensure that sleep health advice is based on reliable and comprehensive information.
Improving Cardiovascular Health
Sleep is one of the health indicators listed in the Life’s Essential 8, the American Heart Association’s measures of optimal cardiovascular health. When including sleep in the Life’s Essential 8 score, the only measure of sleep is its duration (number of hours per night), as there is not yet sufficient validated research to confirm how to assess other sleep components. According to some research studies, poor sleep health (e.g. short sleep duration and irregular sleep times) contributes to negative cardiovascular outcomes. Clinical studies are needed to demonstrate that improving sleep health leads to better cardiometabolic health.
These data could help in the development of effective interventions to improve various sleep components, which in turn promotes better cardiometabolic health. Research studies on multidimensional sleep health should ideally involve the collaboration of different medical specialties, including sleep medicine, cardiology, endocrinology, gastroenterology, nephrology, pulmonology and neurology. In addition, individuals from underrepresented ethnic groups should be included in the studies to capture the various components of sleep health in different populations and communities. A broader understanding and validated research findings on the effects of sleep on physical health and mental well-being are key to improving cardiovascular health for all people.