Are you a morning lark or a night owl? Do you struggle to get out of bed? Is your sleep cycle erratic? Why are teenagers so hard to wake up?

It’s all about rhythm.

“Virtually everything your body does, from the timing of hormones being released to your blood pressure rate, is based on circadian rhythms,” said Theresa Lee, dean of the UT College of Arts and Sciences and professor of psychology.

A circadian rhythm is any biological process driven by the body’s internal daily “clock,” which makes it possible for most living organisms to coordinate their biology with the twenty-four-hour environment.

Lee first discovered the importance of circadian rhythms while studying ground squirrels in the late 1980s. Because the squirrels were in a laboratory, they could not go into deep hibernation. However, Lee observed changes in the timing and amount of daily activity.

“Their behavior got me interested in the circadian rhythms of humans,” Lee explained. “Turns out, there’s a corollary with humans.”

In the Beginning

The first mammals emerged during the time of the dinosaurs. They were primarily nocturnal, which allowed them to avoid predators during the day. Since they were active at night, the various light-sensing organs of their reptile relatives gradually disappeared through evolution—except their eyes.

Humans, like all other organisms, have biological clocks that are not exactly twenty-four hours long. We synchronize to our planet’s light-dark cycles. These cycles reset a “master clock” in the brain, which in turn synchronizes the rhythms of organs, skin, blood cells, etc.

At birth, our circadian rhythm is not yet functional. Newborns usually sleep and eat on continuous two- to four-hour cycles. As their internal clock matures, their daily sleeping patterns develop and they sleep through the night. However, sleep patterns change drastically when children reach adolescence.

“The working theory was that the internal circadian clock got longer than the twenty-four-hour circadian cycle during adolescence or that social behavior was driving late hours,” Lee said. “It turns out that neither is the case. What’s really going on is that the clock begins changing at the onset of puberty and never really stops.”

There is a stable period of circadian control and sleep time between ages four and twelve. “But during adolescence, just when more sleep is needed because of rapid growth, teens find it very difficult to get enough sleep,” Lee explained.

The Teenage Years

Why do adolescents have trouble getting enough sleep? One word: hormones. “Actually, it’s the interaction of the changes in the circadian system caused by hormones conflicting with societal expectations,” Lee said.

Anyone who interacts with a teenager knows that hormonal changes occur rapidly during those years of development. The complicated mechanism of synchronizing the master internal clock becomes even more complex when you throw hormones into the mix. The result is delayed rhythms.

Whether you are now a night owl or a morning person, your sleep cycle became delayed in your teen and early adult years. According to Lee, animal studies demonstrate that it’s not exclusively a human phenomenon. And it occurs in societies around the globe, even those without phones, TVs, or other modern entertainment that can make one want to stay awake.

Teenagers are most alert and learn best in the afternoon and function better when the rest of us are fading. “But because this circadian delay makes it hard to go to sleep at night, they need to sleep later into the morning to get enough sleep,” Lee said.

Sure, they can set alarms and make it to school and work on time, but teens are more likely to oversleep or be late. Some may even become sleep-deprived because of the schedule society requires (particularly early start times at school).

“The amount of sleep we need is pretty stable after we finish growing,” Lee said. “The notion of how much sleep we need and when we need it is probably correct from age twenty to twenty-four to about fifty-five to sixty.”

During that thirty-year span, the average person needs seven to nine hours of sleep at around the same time each night to remain mentally and physically healthy. However, the time of night we prefer to sleep is likely to shift gradually as we age. Everyone recognizes that grandparents typically get up much earlier than younger adults, for example.

Staying Alive

Sleep is an active, complex, and highly regulated process measured in five basic variations in brain activity: stages one and two (light sleep), stages three and four (deep sleep), and REM (sleep characterized by rapid eye movement and dreaming). While we sleep, the body is at its lowest temperature, the immune system is active, and melatonin and growth hormones are released. It is also when the brain removes the debris from a long day of activity, allowing us to awaken renewed.

Lee notes that people who get less than seven hours of sleep are usually the ones who are late or fall asleep at the movies. They take micronaps during the day to make up for lost sleep. They also tend to be moody and unmotivated, and their ability to learn is compromised. “There are lots of negative impacts when we deprive our bodies of sleep,” she added. Our bodies start to break down, and many people with too little sleep or erratic sleep patterns become overweight or show signs of Type 2 diabetes.

“One of the fascinating things researchers report is that when you get older, you tend to lose the deep sleep,” Lee said. “There seems to be a very good correlation between the amount of deep sleep we get as we age and our health.”

Growth hormones released during the deepest part of sleep are necessary for maintenance and repair of the body throughout life. As most folks with elderly parents or grandparents know, sometimes aches and pains can cause older people to wake more often during the night and disrupt deep sleep.

“There’s really no way around the fact that we need a proper amount of sleep and we need to sleep at approximately the same time every day, whether we are young or old,” Lee said.

So if you find yourself having trouble focusing or keeping your eyes open throughout the day, think about your sleeping pattern. Do you get the recommended seven to nine hours a night? Do you go to bed at about the same time each night? If not, a little change could be the natural answer to regaining your rhythm.

Published online, Quest, November 18, 2014