Nature's biological clock - It's not just for women

The biological clock I’m talking about isn’t the one that we hear about in romantic movies, where the thirty-something woman is getting nervous about being single and childless. It’s a far more fundamental mechanism that regulates our sleep-wake cycle.

Animals have this biological clock built in, and they’ve never even read a book about it. Rats will get on their little exercise wheel at the same time every day, and they don’t even have clocks! I know personally that I experience a little drop in energy around 4:00 p.m. and then a rise again around 6:00 p.m., and that seems to be fairly independent of what I do, eat, or drink, though it can certainly be made worse and much more dramatic by the wrong choices.

The rhythm of this internal biological clock is called a circadian rhythm. People who are at odds with it, such as night-shift workers, suffer serious health consequences, not the least of which has to do with their energy and performance.

The circadian rhythm is cycle of roughly twenty-four hours (some say twenty-five) that is in the physiology of almost all living beings, from fungi to people. It was originally coined by a researcher at the University of Minnesota named Franz Halberg, and it comes from the Latin words circa (meaning “around”) and diem (meaning “day”). A circadian rhythm, then, can be thought of as the ebb and flow of different metabolic and biological processes over the course of about a day.

It’s pretty clear, though, that sleep is necessary for our survival, and equally clear that it’s directly, unambiguously, stunningly connected to our daytime energy levels and mood.

Circadian rhythms seem to be generated internally – what scientists call endogenously – even though they can be affected or modified by outside cues such as light. But they are clearly observed in animals such as monkeys, even in the complete absence of external cues. They’re more or less hardwired into our DNA.

So our biological clock, this circadian rhythm, regulated our cycle of sleep and wakefulness. Stanford researchers postulate that this clock has an active alerting function that keeps us up during the day, and then lets us sleep at night by simply turning the alerting function off, or at least that would be what would happen in the best of all possible worlds.

They also theorize that the daytime clock-dependent alerting occurs in two distinct waves-one in the morning when you first wake up, and the other late in the day (which totally accounts for my increased energy around 6:00 p.m.). Finally, they postulate that the second wave of alerting that takes place in the early evening is stronger than the first early morning wave, which makes total sense because by the we will have accumulated more sleep debt and will need a stronger alerting stimulus to overcome it and stay awake into the evening.

Now here’s the good part, and it will blow your mind. In between those two peaks of what the Stanford group calls heightened clock-dependent alerting, the clock operator slacks off and takes, forgive the pun, a nap. Right in the middle of the day, right during the matinee, before it kicks up again for the evening show.

What happens to us around mid-afternoon? We feel tired. Our energy drops. According to the Standford group, most people incorrectly assume that this is the result of eating lunch. Indeed, it can be made way worse by eating the wrong foods for lunch, and it frequently is. But it’s not caused by eating lunch. In reality, says Dement, author of The Promise of Sleep, people are only feeling their accumulated sleep debt, but this time there’s no surge in clock-dependent alerting to mask that feeling.

People who are not sleep deprived at all have accumulated virtually no sleep debt – their credit card bills are paid off. Therefore, when the alerting mechanism takes a nap in mid-afternoon and exposes them to the big bad sleep loan shark who comes to collect, they owe nothing. If on top of that, they also eat right and keep their bodies fit, their mid-afternoon energy slump should be……. Let’s see now ……….. roughly zero.