Fine-tune your sleep | UNC-Chapel Hill

graphic of alarm clock surrounded by sun, moon and stars, along with two individuals

With coming changes of colder weather, shorter days and longer nights, it’s a good time to look at our sleep habits and how we may inadvertently sabotage good sleep and our overall health.

Dr. Brad Vaughn, director of the UNC Sleep Disorders Center in the School of Medicine’s neurology department and professor of neurology, explains how and why we sleep and gives some surprising nuances to common sleep tips.

Why do we sleep?

“We sleep to get the best performance out of our brains,” Vaughn says.

Sleep is a function of the brain. Good sleep contributes to overall healthiness, improved cardiovascular health and reduced risk of stroke and dementia.

The human body, like most organisms, follows a coordinated internal process that regulates sleep and wakefulness in a 24-hour cycle. That cycle is called a circadian rhythm, based on the Latin words “circa” for “around” and “diem” for “day.”

‘Thousands of clocks’

During the cycle, every cell, tissue and organ of our bodies relies on its internal clock to govern its function. But the body needs a master clock.

“Your body is like a room filled with thousands of clocks that need to be set to the same time,” Vaughn says. The brain’s master clock, the suprachiasmatic nucleus, synchronizes all those clocks and controls our circadian rhythm.

Carolina researcher and Nobel-Prize winner Aziz Sancar and his lab found the final pieces to the circadian clock puzzle.

Our bodies learn a schedule through signals from our body’s clock. “It’s there for predictability and enabling the body to anticipate what’s coming up, like your stomach growling when it’s mealtime,” Vaughn says.

Dr. Brad Vaughn

A typical schedule might have a person waking around 6:30 or 7 a.m. and going to bed around 10 or 11 p.m. Based on their body clock, that person will experience deep sleep in recurring periods, especially in the night’s first half. The brain alternates between deep sleep, light sleep and rapid eye movement sleep, progressively increasing REM sleep. These cycles ready our brains for the next day. Our body clock then keeps us awake with noontime peak alertness, a dip shortly thereafter and another peak around 8 or 9 p.m.

During the cycle, your body clock takes cues from bright light, physical activity, food and social interaction. “When you deliver those during the period that you want to be awake, your body learns that time frame,” Vaughn says.

Because the cues can be strong, Vaughn recommends keeping a regular schedule so that the body clock operates robustly.

Sleep’s two drivers

Your circadian rhythm or body clock, which Vaughn describes as “a whole symphony of hormones and regulatory systems timed through the 24 hours of a day,” is one sleep driver. It includes your endocrine system, your autonomic system and the quarter or so of your genes that oscillate, meaning the genes go through a daily process of DNA moving to RNA, from which proteins are created.

In that rhythm, the body signals sleep and wakefulness through a mix of hormones, including melatonin, and the autonomic nervous system, which regulates body processes that occur involuntarily, such as breathing, blood flow and digestion. For instance, a rise in your temperature and blood pressure in the hour and half before you wake prepares you to get up.

Homeostatic drive, a kind of internal pressure that builds during your waking hours, is the second driver. As daily activities fill your brain with waste products and spent energy stores, including a protein called beta-amyloid that is associated with Alzheimer’s disease, homeostatic drive pushes you toward sleep.

The brain craves sleep as a time to replenish energy stores, prune un-needed neuronal connections and flush away byproducts so we can begin the next day with a refreshed brain.

“It’s like cleaning and restocking the kitchen after a full day of cooking,” Vaughn says. “The more you do in that kitchen, the more stuff will build up that you have to clean. Cook less, and you won’t have as much, but your brain will do better if you have an active day.”

As the byproducts build up, the homeostatic drive will eventually overwhelm the body’s ability to stay awake and you’ll get sleepy. When the brain flushes to a low level, you wake up.

“If you wake up before the alarm goes off, guess what? You have not burned off the last bit of homeostatic drive,” Vaughn says. “You’ll start the day with a little higher homeostatic drive, which will build up through the day again, especially if you have a full day.”

If you got enough sleep, your circadian rhythm will override the homeostatic drive to keep you awake in the morning. After lunch, the circadian rhythm slows enough that afternoon drowsiness may come around 2 or 2:30 p.m. In the evening, your body recognizes the wind-down routine.

A look at a night’s sleep

Our brain waves ebb and flow as sleep evolves during the night. Sleep dictates a cycle through deep, light and REM stages in a progression to help your brain be more efficient the next day. Slow waves during deeper sleep indicate that the homeostatic drive is clearing byproducts and re-establishing nutrients and neurotransmitters that our brains need.

We progress through cycles of lighter sleep to more REM sleep. “REM sleep, we think, helps us with associations in memory, such as visually remembering the orientation of something or getting a snapshot, but we still have lots to learn about REM sleep,” Vaughn says.

As the two main drivers — circadian rhythm and homeostatic drive — work, you wake up intermittently for a few seconds throughout the night. “That’s normal,” Vaughn adds. “Going through the process in its evolution is what really helps your brain prepare to be awake.”

Acute versus chronic sleep loss

Have one bad night, but you sleep well otherwise? That’s acute sleep loss. You may feel sleepy the next day, a little off your game or a bit irritable. That’s when a short-term strategy such as caffeine, a brief nap or the body’s stress hormones can help you stay awake.

Chronic sleep deprivation, however, can mess up your life. “If in the long term you constantly get six hours or less a night, after a couple of weeks you won’t perceive that you’re sleepy,” Vaughn says. “You’ll have lapses and be completely unaware of it. You will generally become more depressed and irritable, and your body starts to make changes that impact your health.” For example, you will tend to eat more and likely have issues with blood pressure and other metabolic processes.

To avoid those effects and to help you have the best sleep, consider these tips:

Find your ideal room temperature. Vaughn says that people typically sleep best in a range of 68 to 74 degrees. “Males tend to sleep a little better in the cooler end, and females tend to sleep better in the upper range.”

Get the right amount and kind of light. After waking, spend some time in the sunshine or bright light to help your body know it’s time to get on with the day. In the evening, keep lights low and avoid blue light emitted by LED lights, cell phones and tablets. “At some ages, we’re more vulnerable to blue light. Ten minutes of light from a cell phone in the evening, for instance, can delay a teenager’s body clock by 45 minutes.” Putting the devices away signals to the brain that it’s time to prepare to sleep. People who live in brightly lit neighborhoods sleep 30 to 40 minutes less per night than people in rural areas, Vaughn says.

Nap wisely, if at all. Whether to nap or not depends on your goal. If you are extremely tired and need to complete a task, a 10-minute power nap can help your performance over a short period. “That will push your productivity. The downside is that you may disturb your sleep that night,” Vaughn says. “It’s a short-term strategy, not a long-term solution.”

Limit caffeine. This one sounds tried and true, but there’s more to it. One morning cup can disrupt your sleep that night. “People love coffee, but it is loaded with caffeine. A normal cup of coffee has 50 to 75 milligrams of caffeine. A Starbucks venti has over 400 milligrams,” Vaughn says. “We think of caffeine as being the essence of life, but it’s a short-term strategy that will make you sleep lighter the next night.”

Caffeine blocks the effects of adenosine produced by your body to signal your homeostatic drive. After an initial boost delivered through your bloodstream, the effect weakens in a few hours.

The caffeine that arrives in the brain concerns the neurologist Vaughn. It remains in the brain longer than in blood. “Blood is like the highway, and the brain is the factory. I can measure how much product is out on the highway, but that’s not related much to the amount at my factory.”

A quick metabolizer might get rid of it by evening. “Some people may not metabolize caffeine quickly, and the caffeine will affect them throughout the night,” Vaughn says. “That means less homeostatic drive in a deep-sleep state for cleaning up the byproducts of the day’s activities.”

So don’t let the morning’s caffeine fuel-up keep your cranium factory running overtime.