Sleep 101: Why sleep is so important to your health

A woman sleeps in her bedroom.

By Erica Jansen

Assistant Professor of Nutritional Sciences

March 6, 2026

Editor's Note: This Q&A was updated in March 2026 to include new research findings and expanded guidance on diet, adolescent sleep, and circadian health since its original publication in 2020.

What is sleep exactly, and how does it help us stay healthy?

We all sleep every night and yet when you actually think about how to define sleep, it’s challenging. Usually we’re lying down, but not always. Usually our eyes are closed, but not always. And we might be tempted to say our brains are turned off, but again- not true! In fact, during the REM stage of sleep, our brain activity looks very similar to our wake periods. Regardless of how exactly we define sleep, we do know that it’s essential for keeping us healthy and well in our everyday lives and over the longer term. It is essential for virtually every aspect of our health, from immunity and metabolic health to cognition and mental health. As a mom to young children (who often like to wake me up at night!), I especially notice how clearly sleep is connected to well-being and emotional regulation.

Sleep is an altered state of consciousness where we have limited interactions with our surroundings and are relatively quiet and still (depending on the stage of sleep). Contrary to our quiet physical state, the brain is very active during sleep, carrying out many important functions. Sleep is essential to every process in the body, affecting our physical and mental functioning the next day, our ability to fight disease and develop immunity, and our metabolism and chronic disease risk. Sleep is truly interdisciplinary because it touches every aspect of health.

Sleep is essential to every process in the body, affecting our physical and mental functioning the next day, our ability to fight disease and develop immunity, and our metabolism and chronic disease risk.

How does what we eat impact our sleep?

Over the past 7 years or so, I have been really interested in how individual foods and our overall diets might affect how we sleep. The most consistent finding at this point, including the research conducted by me and my team, is that overall healthier dietary patterns are associated with better sleep quality. Specifically, it is now recognized that diets high in fruits, vegetables, fiber, healthy proteins (like fish and nuts), and dairy may be especially helpful for sleep. It is important to point out that it’s not just what you eat in the hours leading up to bedtime that make a difference- it’s how you eat all day. Although of course, how you eat or drink before sleep is also relevant; the key “bad actors” for our sleep include caffeine, alcohol, and large “late-night” meals consumed in the 1-2 hours before bed, and potentially even longer, depending on the substance, the individual’s tolerance, and metabolism. And while there is a lot of hype about the benefits of certain drinks or sleep-promoting supplements consumed at bedtime (e.g., “Sleepy-Girl Mocktail”), any true effect is likely pretty minimal and rigorous studies on most of these “sleep remedies” are lacking.

It is well-known that certain substances, such as caffeine, can affect the onset of sleep in a negative way. On the other hand, evidence is growing that shows how other foods like tart cherries, kiwi, fatty fish (like salmon and tuna), and malted milk may have beneficial effects on sleep. More recently, studies have shown that healthy dietary patterns overall—not just specific foods—could be associated with longer sleep duration and shorter time to fall asleep.

Why is sleep so important for young children, and what are some of the common negative effects of poor sleep?

Sleep is important for every part of the body, and it is especially important for young children as their bodies and minds develop. In young children, lack of sleep or poor quality sleep can be associated with difficult behaviors, lower capacity to learn and retain information, and a propensity for poor eating patterns and weight gain.

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What sleep needs do adolescents have, and what does this mean for the current conversations we're having around school-day start times?

Adolescents need around 8-10 hours of sleep per night, but a high proportion do not get that amount. For example, the CDC estimates suggest that 60 percent of middle schoolers and 70 percent of high schoolers don’t get adequate sleep on school nights. This figure is even higher for Michigan high schoolers, which is at 80 percent. One of the main reasons adolescents are so sleep-deprived is that biological changes in their brain affect when they feel sleepy. So even if they are sleep-deprived, they often can’t go to bed early because their brain is not yet prepared to sleep. The problem with these delayed bedtimes is that school or before-school activities often start very early,
so adolescents often end up chronically sleep deprived.

In school districts that have enacted later school start times, students get more sleep and as a result have fewer motor vehicle accidents, better grades, and improved mental health.

In school districts that have enacted later school start times, research is consistently showing that students get more sleep and as a result have fewer motor vehicle accidents, better grades, and improved mental health.

Every spring and fall we change our clocks by an hour. What health impacts does this change have on individuals and on the public’s health?

There are many calls from the sleep-research community to eliminate daylight savings time. When our clocks are pushed forward, people lose one hour of sleep. This one-hour sleep loss is associated with significantly more motor vehicle accidents as well as cardiac events. When our
clocks move backward, we might think that an extra hour helps us if we’re usually sleep-deprived. However, there is another factor to consider that is related to our circadian clocks. Any abrupt change in the clock (e.g., like that experienced when you travel across time zones) creates a mismatch between our new sleep and wake times and our internal circadian rhythms, which are still aligned with the daylight savings time. This mismatch is called circadian misalignment, and it is now known to negatively affect health, separately from the effects of insufficient sleep alone. In general, these universal time changes create a significant and negative burden on the public’s health.

How important is sleep for our mental health?

Sleep and mental health go hand-in-hand. Good sleep is essential for maintaining our baseline mental health, as one night of sleep deprivation can dramatically affect mood the next day. Chronic exposure to poor sleep quality is associated with depression, anxiety, and other conditions. There are also bidirectional associations—meaning that experiencing anxiety and depression very often affects sleep, which then impacts our ability to cope with the anxiety and depression, and so on.

How does alcohol impact sleep?

Although alcohol may help a person fall asleep quickly, it hinders sleep quality, often causing fragmented (interrupted) sleep. When consuming alcohol, it is recommended to do so several hours before bedtime so that the alcohol is completely out of the system before sleep.

Does screen time really affect our sleep?

There is evidence to show that screen use right before bed could impact sleep. One reason is that the blue light emitted from these devices can affect the secretion of melatonin, the hormone that helps signal to the body that it is time to fall asleep. Other reasons include the content of what is on the screen. If you watch a scary movie, read an emotionally-driven article, or consume any other anxiety-producing content on your screen, it can affect your ability to fall asleep. Sleep clinicians recommend putting away all screens at least one hour before bed and to instead do some light reading or other relaxing activity.

About the Author

Erica JansenErica Jansen is a nutritional epidemiologist who focuses on diet and sleep in relation to pediatric health. Her research covers how early nutritional environments affect childhood obesity and the timing of puberty, how various aspects of sleep—duration, timing, and quality—affect development of cardiometabolic risk, the bidirectional associations between sleep and diet, and epigenetic markers that underlie relationships between sleep and cardiometabolic health.

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