You spend about a third of your life asleep because your body and brain depend on it to function properly. Just like food, water, and air, sleep fuels your survival.
Scientists are still uncovering exactly why we sleep, but what we know so far is powerful. Quality sleep supports nearly every system in your body. It helps your brain process information, strengthens our memory, balances hormones, repairs tissues, and strengthens your immune system.
When your sleep is disrupted, your health begins to feel the strain, and the impact extends far beyond tiredness. It can influence your blood pressure, immune strength, emotional balance, and even your risk for heart disease.
Let’s break down what happens when you sleep, and why maintaining healthy sleep cycles may be one of the most powerful ways to protect your long-term health.
Every night, your body follows a pattern called a sleep cycle. Each cycle includes stages of NREM (non–rapid eye movement) and REM (rapid eye movement) sleep, which together make up what we call sleep architecture.
Here’s how the 5 stages of sleep work:
A sleep cycle takes roughly 90 to 120 minutes, and you move through several cycles each night. The first half of your night focuses on deep sleep, while the latter half gives you more REM sleep. Both are equally important; one restores your body, the other restores your mind. When your sleep cycles are interrupted, the brain and body lose this rhythm, and the effects of that disrupted cycle can build up over time.
Inside the brain’s hypothalamus, there’s a small cluster of neurons that release a chemical called hypocretin, also known as orexin. This chemical helps regulate your sleep-wake cycle, alerting you during the day and allowing you to rest at night.
When hypocretin levels drop, the brain struggles to maintain stable sleep patterns. This is what happens in narcolepsy, a neurological condition that causes sudden sleep episodes and extreme daytime sleepiness. The loss of hypocretin also affects your reaction time, focus, and mood.
Healthy hypocretin levels, on the other hand, help the brain transition smoothly between wakefulness and rest. That’s why consistent, high-quality sleep supports sharp thinking, emotional balance, and steady energy throughout the day.
During REM sleep, the brain performs essential housekeeping tasks. The hippocampus sorts through memories and transfers them into long-term storage. The amygdala, which manages emotions, works with the prefrontal cortex (the part responsible for reasoning and judgment) to keep emotional responses in check.
If you’re not getting enough REM sleep, you might notice difficulty concentrating, mood swings, or problems with memory. Over time, poor REM quality can affect your mental health, increasing the risk of anxiety or depression.
In neuroscience research, REM sleep and brain function are closely linked to emotional resilience and cognitive performance. Without this stage, the brain can’t process stress or new information effectively.
While REM benefits your brain, deep sleep (also known as slow-wave sleep) is vital for your body. This is when your cells repair, your muscles recover, and your heart and blood vessels get a chance to rest.
During deep sleep, your blood pressure naturally lowers, giving your cardiovascular system a break. Your body also releases growth hormones that repair tissues and strengthen bones. This restorative process allows you to wake up feeling refreshed and physically stable.
When you consistently lose deep sleep, your body experiences more inflammation and hormonal imbalance. That imbalance affects everything from blood sugar control to appetite regulation, often leading to increased cravings and a higher risk for heart disease, high blood pressure, and diabetes.
That’s why the health benefits of a good night’s sleep go far beyond rest. Good sleep protects your heart, stabilizes your metabolism, and strengthens your immune system.
Sleep doesn’t just rest your body; it helps you fight off disease. During slow-wave sleep, your immune system releases proteins called cytokines, which act as messengers to regulate inflammation and immune response.
Your body also increases the production of T-cells, white blood cells that recognize and attack viruses and bacteria. Together, these immune functions peak when you’re in deep, uninterrupted sleep.
When you don’t sleep enough, cytokine production decreases, and T-cell function weakens. This makes you more vulnerable to infections and slows your recovery when you do get sick. Studies have shown that people who sleep fewer than seven hours a night are almost three times more likely to catch a cold than those who sleep eight hours or more.
This sleep and immune system connection becomes especially important during winter, when cold and flu viruses circulate more frequently. Adequate rest gives your immune system time to prepare and respond effectively.
Sleep and health influence each other in powerful ways. Poor sleep contributes to medical conditions like heart disease, high blood pressure, and diabetes, while those same conditions often make it harder to get quality rest.
For example, sleep apnea causes repeated pauses in breathing during the night, lowering oxygen levels and interrupting deep sleep. Over time, this increases strain on your heart and raises blood pressure.
Narcolepsy and idiopathic hypersomnia are neurological disorders that interfere with normal sleep cycles. In narcolepsy, low hypocretin levels disrupt REM transitions, leading to extreme narcoplesy symptoms like daytime sleepiness and fragmented nighttime rest. These changes also affect memory, mood, and overall reaction time.
Meanwhile, mental health conditions like depression or anxiety can alter REM sleep and brain function, making it harder to fall or stay asleep. Research suggests that improving sleep quality may reduce symptoms and even prevent some depressive episodes.
This constant back-and-forth between sleep and disease forms a feedback loop — poor sleep worsens health problems, and those health problems can negatively affect your sleep. Breaking that cycle begins with understanding its importance and seeking care when needed.
You can take steps to strengthen your sleep and protect your health. Here are practical, science-backed ways to improve your rest:
In recent years, neuroscience sleep studies have revealed just how deeply connected sleep is to every system in the body. Researchers are now focusing on how improving sleep quality might help prevent chronic disease and boost mental well-being.
At Science 37, studies are underway to better understand and treat sleep disorders like sleep apnea, narcolepsy, and idiopathic hypersomnia. These trials explore how disrupted sleep affects immune health, cognitive function, and overall recovery. Joining these studies contributes to groundbreaking research that may lead to better treatments and a deeper understanding of how sleep supports life itself.
If you care about your sleep health and want to make a difference, consider participating in a Science 37 clinical trial. Together, we can uncover how sleep cycles, the brain, and the immune system work in harmony to keep you healthy.
