Summary: An American Heart Association scientific statement emphasizes that cardiometabolic health is influenced by more than just sleep duration. The statement also calls for more diverse, interdisciplinary research to establish whether improving these aspects of sleep leads to better cardiometabolic outcomes.

Key takeaways:

• Cardiometabolic risks are associated not just with how long people sleep, but also how well, when, and how regularly they sleep.
• Components such as poor sleep continuity, late bedtimes, low sleep satisfaction, and irregular sleep timing correlate with higher risks of hypertension, obesity, type 2 diabetes, and cardiovascular disease.
• Racial and socioeconomic disparities in sleep health persist across the lifespan, with Black adults experiencing the worst outcomes.
• Clinical conversations about sleep should include qualitative questions about sleep experience, not just sleep hours.
• Current AHA metrics only measure sleep duration due to limited validated data on other components.

Americans frequently consider only sleep duration–how many hours of sleep per night—as a sleep health factor linked to outcomes such as cardiometabolic health, but a new American Heart Association (AHA) scientific statement acknowledges that less-discussed and less-studied components of sleep health are relevant too.

The scientific statement, “Multidimensional Sleep Health: Definitions and Implications for Cardiometabolic Health,” describes multiple components of sleep health, such as sleep continuity, timing, satisfaction, regularity, and daytime functioning. It also reviews the latest evidence on what is known about the relationship between sleep and various cardiometabolic health factors, including body fat, blood sugar, cholesterol, and blood pressure.

“There is increasing evidence that sleep health is about more than the number of hours you sleep each night,” says chair of the scientific statement writing group Marie-Pierre St-Onge, PhD, CCSH, FAHA, in a release.

Components of Sleep Health

According to the scientific statement, no single facet of sleep health fully captures people’s sleep experiences and how their individual body responds. The less-discussed and less-studied components of sleep health are relevant to the sleep experience and contribute to overall physical and mental health and well-being. 

Sleep components includ sleep duration, continuity, timing, satisfaction, regularity, daytime functioning, and architecture.

Sleep Duration

Sleep duration is the number of hours per night (or per 24-hour period) an individual sleeps. It can be estimated via a person’s self-reported number of hours spent sleeping using questionnaires and diaries, or assessed objectively via actigraphy or polysomnography. 

The latest evidence from multiple studies indicates that sleeping less than 7 hours a night increases the risk of atrial fibrillation, cardiometabolic syndrome (a group of conditions that increases the likelihood of type 2 diabetes, heart disease or stroke) and blood pressure that doesn’t decrease as much during sleep (blood pressure should be lower at night/when sleeping versus during the day/when awake and active). 

Too much sleep or sleeping more than 9 hours per night is also associated with an increased risk of cardiometabolic syndrome, stiff arteries, stroke or death from heart disease or stroke.

Sleep Continuity

Sleep continuity is the proportion of time spent sleeping. It is calculated based on factors that represent sleep difficulties, such as the time it takes to fall asleep, how many times a person wakes up during the night, the amount of time spent awake during the night, unplanned early awakening, and obstructive sleep apnea. 

Disturbance in sleep continuity has been associated with a higher risk of atrial fibrillation, heart attack, high blood pressure or more insulin resistance.

Sleep Timing

Sleep timing refers to the time a person typically goes to sleep during a 24-hour period. 

Studies evaluating sleep timing examine how cardiometabolic risk changes with a person’s usual bedtime and whether they are sleeping in the night versus daytime hours. 

High-quality research on sleep timing is limited. However, data indicate that suboptimal timing of sleep is likely to be associated with increased cardiovascular disease risk factors. A reported bedtime of midnight or later, compared to earlier than midnight, has been associated with higher risk of overweight or obesity, insulin resistance and elevated blood pressure.

Sleep Satisfaction

Sleep satisfaction is a person’s own perception of their sleep experience. 

A combined analysis of recent research indicates that lower satisfaction with sleep is associated with higher blood pressure, stiff and less flexible arteries, coronary heart disease and nighttime blood pressure that doesn’t decline.

Sleep Regularity

Sleep regularity is the stability of a person’s sleep duration/timing across days. 

Social jetlag has been associated with a 20% higher risk of having overweight or obesity, and day-to-day variability in sleep timing has been associated with a higher risk of cardiovascular disease, high blood pressure, inflammation, obesity and blood pressure that doesn’t decrease during the night. 

In large-scale studies, greater consistency in sleep-wake timing has been associated with a 22%-57% lower risk of cardiovascular death. In a large UK Biobank study, irregular sleep timing was linked to a higher risk of type 2 diabetes even in people who had sufficient sleep, with the highest risk among those who had too little sleep and very irregular sleep patterns.

Sleep-Related Daytime Functioning

Sleep-related daytime functioning is a person’s ability to remain alert and awake during the day. It can be estimated by participants’ self-reported information about how likely they are to doze off in certain situations (such as watching TV or riding in a car) or by evaluating a person’s cognitive alertness (such as testing reaction time to visual or auditory cues). 

Excessive daytime sleepiness is associated with cardiovascular disease, coronary heart disease, stroke, and death from both 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 sleepiness during the day.

Sleep Architecture

Sleep architecture refers to sleep stages that the body typically cycles through while asleep, assessed using electroencephalography to measure electrical activity in the brain. 

Disruptions in sleep continuity can interfere with sleep stages differently. One analysis of combined studies noted that interrupting non-REM sleep led to higher levels of insulin resistance compared to non-interrupted sleep.

Social and Environmental Factors

The statement also addresses differences in sleep health for people affected by adverse social drivers of health. 

A recent review of more than 300 studies found consistent associations 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 with non-Hispanic white people, individuals in historically underrepresented racial and ethnic groups sleep less and are more likely to experience worse sleep continuity, less satisfaction with sleep, later bedtimes, more irregular sleep, higher daytime sleepiness and a higher occurrence of sleep disorders. These differences are observed across the life span and persist over time, with Black adults having the worst sleep health among all people.

“It’s important to know that every individual has different sleep experiences, and these differences may contribute to other health inequities,” says St-Onge, an 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. “Including different components of sleep in discussions with patients provides essential information that can help health care professionals improve care.”

Asking questions such as:

• “How long does it typically take you to fall asleep each night?”
• “How many times do you wake up during the night?”
• and “How often do you feel exhausted during the day?”

can give patients the opportunity to share concerns about their sleep experience and quality of sleep. 

Documenting sleep details in the patient’s medical records will help the patient’s health care team to be informed about the patient’s sleep health and may prompt more in-depth evaluation or screening. This information is also helpful when considering how a patient’s health conditions and prescribed medication regimen may interfere with sleep health and need to be adjusted or changed.

“Some changes in sleep across the life course are natural, however, individuals should not accept poor or worsening sleep as a ‘fact of life’ or unavoidable consequence of the aging process. If they note new difficulties falling or staying asleep, or excessive daytime sleepiness, they should discuss this with their doctor for further evaluation and potential treatment,” says St-Onge.

More Research Needed to Optimize Sleep Health

Sleep is one of the health metrics noted in Life’s Essential 8, the AHA’s measures for optimal cardiovascular health. When incorporating sleep into the Life’s Essential 8 score, the only measure for sleep is its duration (number of hours per night) because there isn’t enough validated research yet confirming how to assess other sleep components.

According to some research studies, poor sleep health (such as short sleep duration and irregular sleep schedules) contributes to adverse cardiovascular outcomes. There is a need for evidence from clinical trials confirming that improving sleep health leads to better cardiometabolic health. This data could be useful in developing effective interventions to help people improve various components of their sleep, which, in turn, supports better cardiometabolic health.

Research studies on multidimensional sleep health would ideally include collaborative efforts across medical specialties, including sleep medicine, cardiology, endocrinology, gastroenterology, nephrology, pulmonology and neurology.

In addition, individuals from under-represented racial and ethnic groups should be included in studies to capture the various components of sleep health in diverse populations and communities. Broader understanding and validated research about the impact of sleep on physical health and mental well-being are key to advancing cardiovascular health for all.

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