Tick, Tick, Tick
Friday, January 2nd, 2009
Wake up every day at 6 a.m. Deliver a report at a staff meeting at 10 a.m. Eat lunch at 12:15 p.m. Surf the Web for tomorrow’s weather at 3 p.m. Take a 4-mile run at 5:45 p.m. Eat dinner at 7 p.m. Go to sleep at 9 p.m.
Why do we choose to do what we do when we do it? Or are we actually really “choosing” at all?
In her book “Sex Sleep Eat Drink Dream: A Day in the Life of Your Body” (Houghton Mifflin, 2007), science writer Jennifer Ackerman takes the reader on a 24-hour day-trip into the human body as it goes through the motions of work, play, refueling and rest.
From the arousal of the senses in the morning to the reverie of sleep and dreams, Ackerman uncovers the latest findings about the cause and effect of everyday experiences, from stress, fear and fatigue, to sex, exercise and learning. The better we understand our bodies and what’s going on inside them, she attests, the easier it is to maximize the mental and physical potential of each day.
“Most of us are aware of the obvious 24-hour rhythm in our sleep and wake patterns, but we also have daily rhythms in body temperature, heart rate, blood pressure, levels of stress hormones and sex hormones, alertness and even in the workings of the individual cells of our liver, heart, lungs and blood,” Ackerman says. “These rhythms are produced by our internal circadian clocks, little oscillating timekeepers in our bodies.”
In fact, says J. David Glass, Ph.D., a professor of biological sciences at Kent State University, Kent, Ohio, the human body actually has thousands of these small circadian clocks “ticking” away within the endocrine system. Each one functions independently to produce a desired result (digestion, exertion, cell renewal, etc.), but they also are synchronized among themselves for optimal efficiency, output and health. For instance, hunger usually hits at a time when your temperature is higher and therefore more capable of metabolizing food. It’s not simply a matter of being more focused or less weak – there really are, as Ackerman points out, better and worse times of day for certain activities such as eating a big meal, napping, proofreading a manuscript, exercising, going to the dentist, taking medication for your rheumatoid arthritis or even making important decisions.
At the helm of this intricately choreographed ballet is a special part of the brain called the supra-chiasmatic nucleus (SCN); although one could argue that the real master of ceremonies is the sun.
According to the National Sleep Foundation, Washington, D.C., exposure to light stimulates a nerve pathway from the retina in the eye to the SCN in the brain. It sets off a regulated pattern of activities such as raising body temperature and releasing stimulating hormones like cortisol, while also stemming the release of other hormones like melatonin, which is associated with sleep onset, until many hours later when darkness arrives.
One of the interesting aspects of this daily journey, Ackerman points out, is that the body usually experiences a dip in energy during the afternoon, usually between 1 and 3 p.m.
“This is what I call the ‘Doldrums,’” Ackerman says. “When the fog of sleepiness drifts into cloud thinking and you function about as well as if you had quaffed a couple of beers.”
Contrary to what you might think, this drowsiness is not related to what you ate for lunch. No one knows exactly why we experience this afternoon trough, says Ackerman, but some scientists suspect it arises from two opposing processes that reach equilibrium about this time – the homeostatic sleep mechanism, which registers increasing sleep debt, and the circadian alerting mechanism, which has been growing in strength from its low at 3 or 4 a.m.
“Throughout the day, there’s this push-pull process going on – the need for sleep versus the drive for wakefulness,” Ackerman explains. “Around midday, the accumulating pressure for sleep is powerful and the wake signal hasn’t achieved adequate strength to offset sleepiness, so we feel this mountain of drowsiness.”
This natural ebb in energy means the early afternoon is not the best time to, say, give a lecture. Ackerman actually recommends taking an afternoon nap if at all possible – a common occurrence in Spain and other Latin cultures. Research shows that even 15 or 20 minutes of sleep in the afternoon boosts alertness, mood and productivity later in the day.
Once you make it through these hours, your energy starts to rise again, and it is then, in the later afternoon or evening, that you are most likely to maximize your athletic performance. The circadian alerting system is strong, your body temperature is at its highest, your muscles are powerful, your joints are flexible, you breathe your easiest and your heart pumps more efficiently. It’s also when your perception of your own exertion is lowest, so your workout doesn’t feel as difficult.
But keep in mind that this schedule is heavily dependent on normal sleep patterns and proper exposure to light. Without regular light exposure at the right times, the SCN can literally lose its way, making it harder for your body to renew itself mentally and physically.
According to Glass, people who upset their circadian rhythms by working night shifts, such as nurses or factory workers, often suffer from more physical ailments, have more family problems, are more likely to have unhealthy diets, are more prone to alcoholism and have significantly higher rates of morbidity.
“When night shift workers walk out to their cars after work, they experience real sunlight, which confuses their clocks and can make it hard for them to get proper rest,” Glass says. “To make matters worse, they want to socialize with their families during normal hours on weekends and then return to work on Monday night, which is very hard to do because their bodies can’t adjust to the new schedule fast enough. Getting off-track makes them less productive, and more prone to accidents.”
The real crux of the matter is that it is incredibly important to get enough sleep (seven to nine hours), and regularly. As long as plentiful, quality sleep is taken care of, individual circadian rhythms can actually differ.
“Some people are larks,” Ackerman explains, “happily up in the early morning, happily asleep by 8:30 or 9 p.m. – just as an owl is revving up for a long night of wakefulness.
There can be as much as six hours’ difference in the circadian cycles of extreme morning and extreme evening types.”
According to Ackerman, most people fall somewhere in between, with the majority of
Americans tending toward owlishness. (You can find out your own lark/owl chronotype by going to a link on Ackerman’s Web site: www.jenniferackerman.net.) Our circadian rhythms are shaped by small variations in the genes that run our clocks, as well as age and daily exposure to light, both natural and artificial. We may have more owls in our society because of our exposure to nighttime artificial light, which delays our body clocks. If you are looking to “reset” your SCN in order to perform at an optimal level in a nine-to-five world, accomplish more and be your healthiest, the experts agree that exposure to morning light can help advance your clock.
“A brisk walk in the morning can also be just as effective because it boosts Serotonin,” Glass says, “and some people find that taking Melatonin (3 mg tablets) is helpful because it can aid in a more restful sleep. On the other hand, studies have found that both alcohol and marijuana effectively ‘blind’ the body clock to light, thereby disrupting your rhythms, so avoid heavy intake.”
We can’t add more hours to the day, but if we do our best to listen to our bodies and synchronize our actions with our biological rhythms instead of forcing them to follow unnatural routines, when it comes to energy and health, maybe we can turn back the clock.
It may still be your arms, legs and lungs that are doing the work, but the new “intelligent” fitness machines on the market are like virtual personal trainers, taking all the guess work out of achieving optimal fitness and making boring, ineffectual workouts a think of the past.