What is healthy sleep, and who’s at risk of not getting it?

Around one in three adults don’t get enough sleep. And research shows sleep disparities persist across income and racial backgrounds. Getting little or poor sleep won’t just make you tired the next day — it can also increase your risk of heart attacks, early death, cognitive decline, dementia, diabetes, high blood pressure, obesity, depression, and other chronic health conditions.

Clearly, there is a lot on the line with getting good sleep. That’s why last year, the American Heart Association added sleep duration to its list of critical components for optimizing heart and brain health, known as Life’s Essential 8™.

Scientists are still examining how insufficient sleep affects heart health. However, Dr. Michael Grandner, director of the Sleep and Health Research Program at the University of Arizona College of Medicine, says there is robust research on other functions that occur during the major stages of sleep. "When your body doesn't have enough time to do the things it needs to do, it won't do them in an optimal way,” he says.

A healthy sleep cycle

Adults need seven to nine hours of sleep each night, and experts say shaving a couple of hours robs the brain of time it needs to perform vital functions. A healthy adult’s sleep cycle consists of roughly four to six cycles through various stages of sleep. Each stage lasts around 90 minutes.

During the first two stages, the body transitions from being awake to falling asleep. This is called light sleep. As these two stages unfold, your brain waves slow down, and your body temperature and heart rate decrease. Your muscles also start to relax during this stage, preparing you for deeper stages of sleep.

In stages three and four, the body enters deep sleep. During deep sleep, which is also called non-rapid eye movement (NREM) sleep, your brain waves slow down even further while your brain consolidates memories, strengthens neural connections, and repairs and regenerates tissues, muscles, and organs. The space between your neurons also widens, allowing the brain to flush any waste. "This is synaptic pruning, when the brain filters out the junk experiences of the day, the stuff you don't need to learn from long-term," Grandner says.

Growth hormones are also released during this stage, which is important for growth and development, as well as for repair and restoration. Deep sleep is crucial for physical and mental health and is associated with improved immune function, better memory and learning, increased creativity, and reduced stress and anxiety.

Finally, in the rapid eye movement (REM) sleep stage, your body's muscles become temporarily paralyzed, and brain activity increases to a level similar to when you are awake. REM sleep is lighter than NREM sleep and deeper than light sleep. It is also when you dream. REM sleep is crucial for regulating learning, memory, and mood. It is when mental and physical recovery and healing occur.

After REM sleep, the cycle repeats itself, with the body returning to stage one and continuing through the stages until the next REM stage. The body actually cycles through REM and non-REM cycles several times, with increasingly longer periods in REM sleep as the night goes on.

"If you cut your sleep hours short, most of what you've deprived yourself of is REM sleep," Grandner says. Studies show people who are deprived of REM sleep have trouble remembering things they learned before falling asleep. The last stage of sleep is when more mental recovery and healing occur. It's also when the body finishes the physical recovery work begun during deep sleep. “Waking up before the last stage of work cuts corners that can cause problems in the long-term health of the body and brain," he said.

The AHA recommends children ages 5 and younger get 10-16 hours of sleep each day; those 6 to 12 get between nine and 12 hours; and teens get eight to 10 hours. Children and adolescents require more sleep because they are still growing, and the body releases growth hormones during sleep.

Getting good sleep

There are plenty of steps you can take to get a better night's sleep. "Engaging in good sleep hygiene or sleep practices can help to improve sleep,” says Dayna Johnson, an assistant professor and sleep epidemiologist at Emory University's Rollins School of Public Health in Atlanta. “It is important to foster a good sleep environment."

Some helpful tips for good sleep include:

having a consistent bedtime and bedtime routine
sleeping in a dark, quiet room at a comfortable temperature
keeping electronic devices, such as televisions, phones and computers, out of the bedroom

However, some factors that can affect sleep are beyond a person's control, according to Johnson, who studies sleep health disparities.

People with lower incomes are at a greater risk of getting poor sleep. Lower-income neighborhoods tend to have more noise and light, which disrupts sleep. They also tend to have higher levels of air pollution, which can increase inflammation. That inflammation can cause sleep apnea, which makes a good night's rest a challenge.

In addition, people who work minimum-wage jobs often work multiple jobs, or jobs with rotating, inconsistent shifts. These things make it harder to develop a consistent sleep routine, Johnson says.

Structural racism plays a role in these disparities, as it has been shown to affect neighborhood environments, leading to problems such as poorer air quality and housing. Additionally, Black people with higher education, higher-paying jobs, and homes in higher-earning neighborhoods have been shown to have poorer sleep health than their white peers, Johnson says.

She led a 2019 review of an extensive body of research outlining racial and ethnic disparities in sleep duration and quality. The review found that Black, Hispanic and Chinese adults were disproportionately more likely to get under six hours of sleep each night. They were also more likely to report poor sleep quality.

"The determinants of sleep disparities are multifactorial, and the worse sleep among higher SES Black adults may be due to increased exposure to racism/stress from being a minority in the workplace or neighborhood," she said. "There are many reasons someone may have poor sleep."

Whatever your situation, it is crucial to understand which underlying causes of sleep disparities you are up against and do what you can to prioritize good quality sleep.