Circadian rhythms are powerful, but people can change their sleep-wake cycles

(Cathy Gendron)
By Carolyn Butler
Tuesday, June 29, 2010

No matter what I do, and despite the fact that my baby has arisen at the crack of dawn for well over a year now, I just can't seem to turn myself into a morning person.

My body simply refuses to shut down much before midnight, and so I work, pay bills and watch terrible reality-TV reruns until the wee hours, only to be dog-tired and disagreeable come 6 a.m., when my live little alarm clock begins wailing for me. Even when I force myself to go to bed on the early side or when my husband lets me sleep in on a Saturday, waking up always seems a chore.

My brother-in-law, on the other hand, is known for unabashedly yawning in people's faces starting right around 8:30 at night, whether he's at home, a family dinner or the theater. I ran into him bright and early the other morning on my way to Starbucks, when I was so beat that I could barely communicate -- and he was clear-eyed and chipper, heading off on a long run.

What makes one person greet the day with smiles and energy, and another hide under the covers until the last possible moment? It's a combination of genetics, the environment and our lifestyle choices, says sleep specialist Mark Wu, an assistant professor in neurology at Johns Hopkins Medicine. He explains that your body's natural circadian rhythms, which cycle up and down over an average 24.1 hours, control sleep and wakefulness and differ from person to person. How much sleep you've had lately also makes a difference, influencing how great your body's drive for more shut-eye is.

"We believe genetic factors are at play [in these issues], but it's complex; we can't pin it down to one gene right now for the average night owl or morning person," says Wu.

Circadian rhythms are influenced by your environment -- in particular, by light exposure, which adjusts your body clock and suppresses the release of melatonin, a natural hormone that signals to your body that it's time to sleep, says Charles Czeisler, director of the division of sleep medicine at Harvard Medical School. That's one reason a lot of folks find it easier to get up in the summer, when the sun rises at an earlier hour, he explains, and why ever-present artificial light, in the form of computers, televisions and the like, "has shifted our whole society three to four hours later, and made it much more difficult to go to bed earlier, for the average person." Then, says Wu, there are the lifestyle choices you make, including how much sleep you get overall, your caffeine intake and when in the 24-hour daily cycle you work, socialize and eat meals.

According to Helene Emsellem, director of the Center for Sleep and Wake Disorders in Chevy Chase, sleep patterns change as we age. She points out that most teenagers are naturally night owls, which scientists think is probably due to hormonal changes. (It's also a phenomenon that has been observed in adolescent rodents, rhesus monkeys and other animals.) But most of us start to rise earlier as we get older, due to our changing body clocks as well as work schedules, changing family needs and the like.

"There is clearly a shift in the timing of the sleep period to a later start time in association with puberty, which we see in at least two-thirds of adolescents," Emsellem explains. "It's a very real event; it's not just that teenagers are lazy or difficult. There's a strong biological tendency to wake up later and go to sleep later, just like there's a biological tendency for older people to advance their body clocks and wake up earlier, and then go to bed earlier." These natural tendencies are then reinforced by teenage rites of passage such as staying up late to chat with friends and partying till the wee hours.

Not the best argument for those early high school start times, huh?

Similar factors can also make it tough for many recent college graduates -- who are accustomed to all-nighters, parties that begin only when much of the rest of the world is heading to bed, and erratic, unregimented sleep schedules -- to readjust their systems and join the real world. "College students still have that biological tendency to go to bed later and wake up later and, like most Americans, are living with chronic sleep debt, which can make it really difficult to make it to a job by 8 or 9 in the morning," says Wu. "Because of that, they need to . . . really focus on sleep routine -- and regimen."

Indeed, he and other experts say it is possible for most of us to change our sleeping habits, with a little bit of concerted effort. Emsellem recommends a four-step plan because "when it comes to adjusting circadian rhythm, you really want to hit your system in every way it's operating." Her tips:

1. Set your wake-up time -- and then stick to it like glue. Ideally you should get up at the same time every morning, including -- gasp! -- those precious weekends. If you sleep more than 90 minutes later on a Saturday or Sunday, says Emsellem, you will affect your body clock, readjusting it to the later wake-up time just as you have to get up early again Monday morning.

2. Seek light. Immediately upon awakening, expose yourself to bright light for at least 20 minutes, either by walking or exercising outside or using a special light box or portable light visor around the house, with approximately 10,000 lux of light.

3. Try melatonin. It's important to discuss this first with you doctor, but for many people, taking this over-the-counter supplement -- a synthetic version of the natural hormone -- about six hours before you want to go to sleep can help regulate your body clock.

4. Put yourself in a position where you can sleep. Avoid eating, alcohol, caffeine and exercise, which rev up the body, for at least a few hours before bedtime, and then turn off the TV, power down the Internet and get off the phone, says Emsellem. Instead, turn to your MP3 player for some mellow music or a "boring" book on tape. That way you'll evade additional light exposure and be able to start winding down. "If you keep moving, keep doing things, you're going to override any sleep signals you want to be reinforcing," she explains.

It's not easy, but these things do make a difference for many people. I've been forcing myself to get up and get outside just after sunrise for a few weeks now, and while I still don't relish the hour, I am starting to appreciate things such as morning's lower heat and humidity and the manic chorus of birdsong. As an added bonus, I no longer snarl at my husband or any peppy passersby when they smile and say, "Good morning"; I just nod and try my best to agree.

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