Sleep as a determinant of health

When Robert Thomas, MD, started his training in sleep medicine in the 1990s, many physicians considered it a niche specialty with little influence on population health.

“The mentality was: ‘Sleep medicine? Who cares? It’s such a small thing,’” Thomas recalls. “It has evolved in interest and importance over the last 25 years.”

Though sleep is a basic human need finetuned over millions of years of evolution to enable almost all the body’s daily functioning, “modern life is pretty bad for sleep,” says Thomas, a professor of medicine at Harvard Medical School who co-directs the Sleep Disorders Center at Beth Israel Deaconess Medical Center in Boston.

Electricity, computers, smartphones, overnight and irregular shift work, and the ability to travel and communicate across time zones — as well as mental and physical health issues — have disrupted the natural course of sleep for an estimated 50-70 million people in the United States alone, according to the National Heart, Lung, and Blood Institute. And sleep deficiency is linked to chronic health problems, including heart disease, kidney disease, high blood pressure, diabetes, stroke, obesity, and depression. It is also linked to accidents that can result in injury or death.

Many people suffer from poor sleep routines and experience both short- and long-term health effects, but some people are even less likely to get adequate sleep, particularly Black and Latino people, people with low socioeconomic status, and people who work overnight or irregular shifts over long periods.

And while research and understanding of sleep and its importance for health is increasing, the medical field has not yet caught up to the needs for screening for, diagnosing, and treating sleep disorders, Thomas says.

“So far, sleep [disorders have] been considered something unusual to directly deal with in common general or specialized practice,” he says. “Patients are best served by sleep assessment being an integral, normalized part of most areas of medicine, such as neurology, cardiology, pulmonology, and psychiatry.”

The science of sleep

The human body and brain are wired to function on a 24-hour cycle, throughout which biological mechanisms known as circadian rhythms dictate fluctuations in wakefulness, body temperature, metabolism, release of hormones, gene expression, and more. These rhythms are highly influenced by light and darkness, which signal the brain when it’s time to be awake and when it’s time to wind down for sleep.

Sleep consists of cycling repeatedly through two phases: non-REM (rapid eye movement) sleep, during which the body’s temperature drops and heart rate, breathing, and brain waves show complex combinations of slow and fast patterns; and REM sleep, when the body is paralyzed as the brain waves, breathing, and heart rate quicken and when dreaming occurs. Adequate quantity, quality, and timing of both types of sleep have complementary roles for brain and body health, Thomas explains.

Researchers believe the brain may clear out toxins, parse through and store memories, and regulate immune processes, among other essential tasks, during sleep.

Scientists have also observed the effects of lack of sleep: diminished attention and cognitive processing, increased risk of motor vehicle crashes, high blood pressure, memory loss, increased risk of mental illness, and increased risk for several chronic conditions, including heart disease and diabetes.

“There is a lot of literature showing sleep is fundamental to biological and psychological and behavioral processes,” says Ze Wang, PhD, a professor at the University of Maryland School of Medicine in Baltimore.

Wang is leading a research team that is observing how insufficient sleep impacts mental and behavioral health in children and adolescents using data obtained over a 10-year period. After studying data collected from the children during a two-year period, the team found that insufficient sleep (less than 9 hours per night) is associated with less grey matter in the brain, worse cognition scores, and severe behavioral problems.

“Factors that can contribute to insufficient sleep can be environmental, familial [conflict], socioeconomic, social media [use], and [lack of] physical activity,” among others, Wang says.

He adds that school policies that require children to wake up early or stay up late doing homework, as well as the increase in smartphone use among children, can be major contributors to deficiencies.

Though he stresses the study is observational, it does suggest the far-reaching impact that sleep deficiency can have, starting early in life, and how powerful an impact a person’s environment can have on their well-being.

Sleep inequity

With growing recognition of the impact of social determinants of health on a person’s well-being, many in the medical field are familiar with how issues such as food insecurity, poor quality housing, and lack of access to education can interplay with a person’s ability to prevent and treat health problems. But fewer people think to include adequate sleep in the equation for social determinants of health.

When the National Institute on Minority Health and Health Disparities was formed in 2000, it was looking primarily at racial disparities in cancer, HIV, and heart disease incidence and outcomes, says Girardin Jean-Louis, PhD, a professor in the Departments of Psychiatry and Neurology at the Miller School of Medicine, University of Miami in Florida.

“We were not thinking about sleep, necessarily,” he explains.

Over the past 23 years, however, research into the importance of sleep health, including his own research into racial and ethnic disparities in diagnosis and access to treatment of sleep disorders, has highlighted how intimately sleep plays into health equity.

“It used to be that the attitude [in the medical field] was that if you have a heart problem, you have to take care of that. If you have high blood pressure or diabetes, that must be treated, but if you say you couldn’t sleep, that’s not going to kill anybody. Well, that’s not really true.”

Girardin Jean-Louis, PhD
Miller School of Medicine, University of Miami

Black people and Hispanic people are more likely to report getting less than six hours of sleep each night — less than the seven to eight hours that is recommended — than White people, and Black people are less likely than White people to be diagnosed with and receive treatment for a sleep disorder, such as sleep apnea. One 2018 study found that, though sleep apnea (when a person stops and restarts breathing while sleeping) is far more prevalent in Black people than White people, as many as 95% of Black people with sleep apnea go undiagnosed.

Jean-Louis says that the reasons behind this underdiagnosis and treatment of sleep disorders in the Black community echo the same reasons they are undertreated for other health problems such as cancer.

People who face barriers to accessing health care, such as having experienced racism in a health care setting, lacking insurance coverage, being unable to get time off work, or lacking child care or transportation, are less likely to take the additional steps needed to seek help for a sleep disorder, he says.

When sleep clinics are based in hospitals, which some in minoritized communities distrust, or when they are staffed by mostly White people or people who cannot communicate effectively to a person coming into the clinic, they create barriers to diagnosis and treatment, Jean-Louis says.

The key, he says, is in making interventions accessible to the communities that need them most. This work is still in early stages, but some researchers are developing models to better engage underserved communities with sleep health education, implementing sleep screening for high-risk individuals during hospitalizations, using telemedicine, and empowering primary care and other health care providers to be well-educated on sleep health and sleep disorders.

“It used to be that the attitude [in the medical field] was that if you have a heart problem, you have to take care of that. If you have high blood pressure or diabetes, that must be treated, but if you say you couldn’t sleep, that’s not going to kill anybody. Well, that’s not really true,” Jean-Louis says. “More people are becoming aware now that sleep is important.”

Sleep in medical school curricula

Not only is raising awareness of the impact of sleep on health essential to improving health care for patients, it’s also an important focus for many physicians — particularly those in training — on both a professional and personal level.

Rachel Salas, MD, a sleep medicine specialist and assistant medical director of the Johns Hopkins Center for Sleep and Wellness in Baltimore, Maryland, says that part of the problem is that sleep medicine receives little attention during medical training. This reinforces the idea that sleep is unimportant and perpetuates poor sleeping habits for the medical trainees themselves, who are often on work schedules that make regular, good sleep difficult to maintain.

“A lot of people think they’re special and don’t need that much sleep,” Salas says.

She has worked to change this by creating a sleep medicine curriculum housed within the neurology department at Johns Hopkins University School of Medicine and giving guidance to other training programs on how to enhance their own curriculum. In recent years, she’s noticed an increase in attention to sleep health in the academic medical field.

“Ten years ago, medical students only got an average of 0–2 hours of education on sleep,” Salas says. “[Now], a lot of national education organizations are coming together to make sure to include sleep in training, whatever the specialty.”

She hopes that the additional education will not only help the next generation of doctors to better serve their patients, but will encourage physicians to take better care of their own sleep as well.

“Sleep is one of those things that crosses all fields. It’s a basic human need.”

Rachel Salas, MD
Johns Hopkins Center for Sleep and Wellness

Laura Barger, PhD, a part-time assistant professor of medicine at Harvard Medical School, is leading an ongoing study that has evaluated data for first-year medical residents during various periods over the past 20 years. She found that extended shifts are associated with an increase in significant medical errors and adverse events.

The study influenced a temporary change in regulation that limited first-year residents to 16-hour shifts, but that regulation has since been lifted, Barger says. Her team is currently analyzing data collected from 2020 through this year.

Salas says that today’s medical students are very interested in learning about sleep medicine because they’ve felt and witnessed the effects of poor sleep on themselves and their own communities.

“Sleep disorders are so common, they’ve seen them in their own mentees and learners, their families,” she says. “Sleep is one of those things that crosses all fields. It’s a basic human need.”