Did you sleep well last night? If not, you’re in good company. About a third of American adults don’t get the recommended seven hours of sleep per night, according to the Centers for Disease Control and Prevention. Many people don’t get enough sleep or sleep poorly because of their jobs or hectic schedules — they work long shifts at night or have to rush to get their kids ready to catch a 6 a.m. school bus. Some 50 million to 70 million Americans have a chronic sleep disorder such as insomnia or sleep apnea, a condition in which breathing repeatedly stops and starts throughout the night.
Scientists still fiercely debate sleep’s fundamental biological purpose. In people, however, plentiful evidence suggests that sleep performs a range of vital functions, including restoring damaged tissues, boosting learning and memory, and flushing toxins from the brain. Sleeping too little can have serious long-term health consequences, increasing the risk of obesity, diabetes and cardiovascular disease.
A new study in Pediatrics highlights the importance of sleep for teenagers, who often struggle to get the recommended eight to nine hours per night of shut-eye. Out of the more than 800 adolescents in the study, only 2.2 percent got enough sleep, and less than half achieved desirable rates of “sleep efficiency” — the percentage of total time in bed actually spent asleep.
Teens short on sleep were more likely to be obese — a trend found in previous studies — and scored higher on several other risk factors for cardiovascular disease, such as high blood pressure and poor glucose metabolism. Those who slept longer and better tended to have less fat around their waists, lower systolic blood pressure and higher levels of “good” cholesterol — all signs of cardiovascular health.
Knowable Magazine called one of the study authors, physician Susan Redline of Brigham and Women’s Hospital, to discuss sleep’s powerful influence on our hearts and other body systems, a subject Redline also wrote about in the 2015 Annual Review of Public Health. To reduce our society’s high rates of chronic disease, she says, we need to ensure children get better sleep, as well as other sleep-deprived groups such as minorities and shift workers.
This discussion has been edited for clarity and length.
How did you become interested in studying the health impacts of sleep?
I was trained in pulmonary medicine in the mid-’80s, shortly after a new therapy for sleep apnea — the Continuous Positive Airway Pressure (CPAP) device — had been developed. Prior to CPAP, patients had to undergo surgery and have tracheostomies and lose the function of their voices. It was very exciting to see a therapy that, literally overnight, could change a person from being very sleepy and having poorly controlled hypertension and even heart failure to someone who was functional.
I sought out training in epidemiology and observed how little we understood about the population prevalence and risk factors for sleep apnea. That's when I started developing epidemiologic studies to address those questions. I also became interested in other aspects of sleep, such as the genetics of sleep apnea, insomnia, sleep and children, and the impact of sleep on heart disease.
How does poor sleep affect the heart and other aspects of health?
Having an adequate quantity of sleep as well as quality of sleep is important for maintaining numerous body systems. Compared with people who get seven or eight hours of sleep per night, for example, short sleepers have a 10 percent to 30 percent increased risk of cardiovascular disease.
Getting insufficient sleep — in general less than six hours a night for adults — may trigger the release of various proteins that cause inflammation in the blood and in the body, and cause dysregulation of the immune system. C-reactive protein, interleukin 6, and tumor necrosis factor are three commonly measured inflammatory markers that are increased in association with sleep problems. These inflammatory mediators may also make you less sensitive to insulin, which then will raise your blood sugar and can lead to diabetes.
A second problem is getting insufficient amounts of deep sleep, or restorative sleep. In one of the deepest stages, called slow-wave sleep, there is a drop in the level of catecholamine hormones that raise blood pressure, such as adrenaline. People with sleep disorders have what we call arousals — very brief periods of awakening. When you have fragmented sleep, high levels of these hormones can prevent blood pressure from going down. Over time, this can cause stiffening of the heart muscle.
Your recent study in Pediatrics showed that lack of sleep increases risk factors for heart disease in adolescents. Do children and teenagers need to sleep the same amount as adults?
Infants typically need more than 12 hours of sleep, then by the time you’re an adolescent those needs are closer to eight or nine hours. An average adult needs between seven and eight.
What was really interesting about this recent study was that we were able to show that both insufficient sleep and misaligned sleep — sleep that isn’t in sync with a person’s circadian rhythm — are associated with metabolic parameters associated with increased risk of diabetes and heart disease, such as higher central body fat.
This study adds to evidence that improving both children’s sleep duration and making their sleep patterns more regular may, over time, protect children from developing metabolic problems.
What are the most common sleep disorders? How can you tell if someone has a sleep disorder or is just staying up too late?
The two most common sleep disorders are sleep apnea and insomnia. Sleep apnea is when your throat closes during sleep for brief but repetitive periods of time, interfering with your ability to get oxygen into your body and to rid your body of waste products like carbon dioxide. Insomnia is a disorder where individuals have chronic problems falling asleep or maintaining their sleep. Another relatively common sleep disorder is called periodic limb movement disorder, where the individual has disrupted sleep because of involuntary kicking of their legs or arms that wakes them up.
Although there is a continuum of symptoms, usually a sign of a disorder is a persistent feeling of tiredness, sleepiness or unrefreshing sleep that isn't explained by another factor like being out all night at a party or working. It's the persistence of daytime symptoms without a clear explanation.
Are some racial or ethnic groups more at risk of chronic disease as a result of poor or inadequate sleep?
In the US, the prevalence of short sleep and poor sleep quality is much higher in ethnic minorities than in the white population. Blacks are as much as five times as likely to report short durations of sleep than whites, for example. That doesn't seem to be completely explained by known sleep disorders, so it suggests there may be multiple social and environmental factors that influence poor sleep quality, such as living in disadvantaged neighborhoods.
One of my interests is in sleep apnea in children. African-American children have much higher rates of sleep apnea than white children, and they actually appear to respond less well to the usual surgery that's done, tonsillectomy, than white children. I've postulated that having sleep apnea at an early age, and going years with untreated sleep apnea, may be one reason that we see much higher rates of hypertension and early-onset hypertension in African-American communities, which is a huge risk factor for stroke and heart disease.
So far, we have shown in two different studies that children who live in disadvantaged neighborhoods have higher rates of sleep apnea than other children. Right now we're doing a study in Boston where we are going into the homes of children from diverse neighborhoods in the city and looking to see if there are actually excessive exposures to various allergens, irritants or poor air quality that may be triggering chronic inflammation of the nasal passages and the tonsils that might be contributing to sleep apnea.
What are some things that can be done to improve sleep health?
Institutionally, we could work harder to ensure that we don't require students or workers to follow unhealthy sleep habits. We could delay school start times so that students don’t have to get up to catch a school bus at 6 a.m., for example. I also work with a group of patient advocates who have suggested that everybody who gets a driver’s license be educated on sleep disorders and the impact of drowsy driving — and to consider including screening for sleep disorders as a part of applying for a license.
What are the most compelling unanswered questions about sleep?
One question I’m interested in is the variation in susceptibility to sleep disorders — what factors may be inherited or otherwise. I think the question of why African-American children have much more severe sleep apnea than other children is really important, both as a mechanistic and a public health question.