Sleep Essentials: What is Sleep and Why it Matters

Sleep is an active process that helps keep our brain and body healthy. It is closely connected to our circadian rhythm, the internal body clock that helps regulate when we sleep and wake up. Our bodies do not simply switch “on” during the day and “off” at night.

Throughout the day and night, our internal body clock helps regulate important functions, including hormone release, digestion, and body temperature. Sleep is an essential part of this daily pattern. When sleep or circadian rhythms are disrupted, it can affect how we feel and function throughout the day.

Thinking about sleep as part of our overall health, rather than just something that happens at night, can help us make positive changes. By understanding how our daily habits affect sleep and circadian health, we can take steps toward better health and wellbeing. This is what it means to own all 24 hours.

This page introduces the basics of sleep, including what happens while we sleep and why healthy sleep is so important. It also explores how sleep affects individuals and communities, with opportunities to learn more about each topic.

Sleep is a natural process during which we become less aware of our surroundings, while our brain and body continue to carry out essential functions.

Although sleep may look quiet from the outside, it is not passive. The sleeping brain remains active, and the body continues to regulate many processes that support health and function.

Sleep is shaped by at least two major systems:

• Sleep pressure: The longer we stay awake, the stronger our natural need for sleep becomes. A substance called adenosine builds up in the brain while we are awake and helps signal when it is time to sleep.
• Circadian timing: The body’s internal clock helps time sleep and wakefulness across the 24-hour day. Light, meals, activity, social schedules, and daily routines can all help shift or reinforce this timing system.

Healthy sleep is easier when our need for sleep and our internal body clock work together. When they are out of sync, we may struggle to fall asleep, stay asleep, or feel alert during the day.

During the night, we move through four stages of sleep, which are grouped into two main types: non-rapid eye movement (non-REM) sleep and rapid eye movement (REM) sleep.

Non-REM sleep includes three stages, from light sleep to deep sleep. As we move through these stages, our heart rate and breathing slow down, and our body becomes more relaxed. Deep sleep is particularly important for physical recovery and restoration.

REM sleep is the stage when most vivid dreaming occurs. During REM sleep, our brain becomes highly active, our eyes move rapidly beneath our eyelids, and most of our muscles temporarily relax to the point that we cannot move them. This stage is closely involved in memory and emotional processing.

We move through these stages several times each night, following cycles that typically last around 90 minutes. Each stage contributes to healthy sleep, supporting our brain and body in different ways.

Sleep is essential for our physical and mental health, just like healthy eating and regular exercise. Getting enough good-quality sleep helps us feel better, think clearly, and function throughout the day.

Healthy sleep supports many aspects of our health, including:

• Learning and memory
• Mood and mental health
• Daytime attention and safety
• Immune function
• Metabolism and hormones
• Heart and blood vessel health
• Growth, repair, and recovery

When we don’t get the sleep we need, these functions can be affected. Over time, regularly getting too little sleep or experiencing poor-quality sleep can increase the risk of certain health problems.

Sleep is influenced by these rhythms, but also by how long we have been awake. For healthy sleep, our need for sleep and our internal body clock need to work together.

This explains why getting enough hours of sleep is not always enough. When we sleep at times that do not match our internal body clock, we can still feel tired or have trouble sleeping. This can happen with shift work, jet lag, or irregular sleep schedules.

Understanding how sleep and circadian rhythms work together can help us make positive changes to our daily routines. By supporting our health throughout the day and night, we can take greater control of our wellbeing and own all 24 hours.

Sleep problems are common in the United States and around the world. Despite growing awareness of the importance of sleep, millions of people regularly struggle to get the sleep they need.

In the U.S., nearly one in three adults (30.5%) get fewer than the recommended seven hours of sleep per day. According to a 2024 national survey, only about 55% of adults wake up feeling well-rested most days. These findings show that both the amount and quality of sleep remain widespread concerns.

Sleep problems are also a global health challenge. A 2025 scientific review estimated that 16% of adults worldwide, or approximately 850 million people, experience chronic insomnia. This means they regularly struggle to fall asleep or stay asleep, with effects on their daytime wellbeing.

These figures show why healthy sleep deserves greater attention as a public health priority. Improving sleep health means not only helping individuals develop healthy habits, but also addressing the conditions that make good sleep difficult for many people.

Everyone deserves the opportunity to get healthy sleep. But not everyone has the same ability to do so. While healthy sleep habits are important, the conditions in which we live and work can make it difficult to get the sleep we need.

For example, people working night shifts or multiple jobs often have less control over their sleep schedules. Others live in noisy neighborhoods or crowded housing where getting restful sleep is difficult. Financial stress and caregiving responsibilities can also interfere with sleep.

These challenges can have lasting effects. When people regularly struggle to get enough sleep, their risk of developing health problems can increase. Limited access to healthcare can make it even harder to recognize and treat sleep disorders, allowing problems to continue without proper support.

Sleep equity means that everyone should have a fair opportunity to get healthy sleep, regardless of their income or living circumstances. Achieving this requires more than encouraging better sleep habits. It also means creating healthier living environments, improving access to sleep healthcare, and supporting workplace and community policies that protect sleep.

By recognizing these challenges, we can work toward a society where healthy sleep is possible for everyone.