Q: Is it true that we can tell time in our sleep?
A: Absolutely. This is why we sometimes wake up two or three minutes before the alarm goes off, an amazing feat when you think about it. However, the brain’s performance in the first half hour after waking is worse than it is if you’ve been up for 24 hours. And as for that morning cup of joe, the caffeine works not by exciting nerve cells but by foiling the process by which they are calmed.
Q: When is your brain at its peak performance?
A: For many of us, late morning is the optimal time for mental performance, though it varies depending on whether you’re a lark or an owl: Alertness and memory—the ability to think clearly and learn—can vary by as much as 30 percent over the course of the day. For morning types, concentration tends to peak between 10 a.m. and 12 p.m., along with logical reasoning and the ability to solve complex problems.
Q: You talk about the body being rhythmic. What do you mean?
A: Our bodies beat to the drum of a 24-hour circadian rhythm. We all carry within us little timekeeping circadian clocks that generate a 24-hour rhythm and keep the body running on this daily schedule—even if we’re locked up in a closet or sitting in a dark cave somewhere, with no cues, like light, from the environment. Thanks to these clocks, there really are better and worse times of day to study for an exam, take a nap, get a tooth pulled, or run a race.
Q: Just what are larks and owls?
A: Well, the world divides between those who shine at dawn and those who side with the night. I’m a confirmed lark, a real morning person, so I like to wake up just a few hours after an owl, an evening person, is going to bed. Everyone’s circadian rhythms are different, shaped by small genetic variations and also, by age and exposure to natural light. There can be six hours’ difference in the cycles of morning and evening people. Owls suffer a lot more in our 9-to-5 society than larks do. And though your bird type is probably shaped by your genes, you can do a thing or two to adjust your clock. There’s a great website run out of Columbia University where you can determine the nature of your own body clock and learn how to shift it: www.cet.org.
Q: I remember being in college, staying up all night and cramming for a test. How well does that really work?
A: Not well. In fact, new research shows that getting a good night’s sleep after learning something new is vital to the brain’s ability to organize the information and reinforce memory. Far better to listen to your mother and "sleep on it."
Q: Is it important to nap?
A: The Inuit may have 20 words for snow, but those champion nappers, the Pukapukan of New Zealand, have more than 35 words for dozing, depending on the soundness and the position or movement of the sleeper. Naps have achieved new status among researchers: study after study has demonstrated that naps enhance alertness, mood, vigilance, and productivity in the later hours of the day, especially for nightshift workers and those forced to work for long periods. The optimal time and length of a nap varies depending on your needs. But 15 to 30 minutes between 1 and 3 p.m. does wonders for most of us.
Q: Why not longer, and why at that time?
A: Actually, longer naps are great, too. According to Sara Mednick of the Salk Institute, a 90-minute nap can boost your energy, alertness, and creativity by providing you with both REM sleep and slow-wave sleep. But many people can’t build a long nap into their days. Also, you’re groggier when you wake up from a longer nap. The reason you crave sleep after lunch is not because of that big pasta salad you ate, but because your body experiences a natural dip in alertness in the afternoon—whether or not you ate lunch.You can either fight the dozing impulse with a cup of coffee or a brisk walk. Or you can give into it and steal a little snooze. I heartily endorse the nap route—you’ll wake up smarter, healthier, and safer.
Q: A lot of people believe the best time to exercise is in the morning, when you’re fresh. Is that right?
A: No. In fact, afternoon or early evening is best if you want to beat your time on a 5k or nab that freestyle medal. Late in the day is when your body temperature is highest, your muscles most powerful, and your joints most flexible. It’s when you breathe easiest and when your heart is pumping most efficiently. It’s also when your perception of your own exertion is lowest, so your workout doesn’t feel so beastly. But of course, the best time to exercise is when it’s most enjoyable and convenient for you. That way, you’ll stick with the program and make it a regular habit. If you want to burn calories, timing doesn’t matter. But body composition does. Muscles burn more calories than fat.
Q: This raises the question: What’s the best time to eat if you don’t want to put on the pounds?
A: Morning, definitely. A big breakfast is the way to go. Not only does the body empty breakfast from the stomach 50 percent faster than it empties dinner, but it seems to process calories more efficiently early in the day. Also, some studies suggest that morning meals satisfy our hunger better, so if we have a big breakfast, we don’t eat as much over the course of the day. This may be because the brain’s satiety mechanisms function best early in the day.
Q: And what about the best time to drink? Is there any biological advantage to the cocktail hour?
A: Yes, oddly enough, the time of day we choose to have our booze—evening—is coincidentally the time when our bodies best tolerate alcohol. Time of day influences how quickly alcohol is metabolized in the body, and how much it affects our organs and our faculties. A shot of vodka early in the day is more intoxicating than the same shot at twilight.
Q: And is there an ideal time for sex?
A: There are two popular times of day for sex: For most of us, it’s late at night, after 11 p.m., with early morning a distant second. This is ironic because testosterone levels peak in the early morning, which would seem to fire things up. But the truth is, our sexual activity is dictated by the clock on our nightstand, not the one inside our bodies. We tend to have sex at night due to work and family schedules, not circadian cycles in fertility or sexual desire.
Q: You write about the “hour of the wolf.” What is this?
A: It’s that stretch of time in the early, early morning, well before the sun rises, when body temperature hits a low point, along with the workings of both body and mind. Sometime between 3 and 4 a.m. is a peak hour for errors among people doing night work, for auto and truck crashes, for congestive heart failure, and for despair—for ruing that big mortgage you took on or those sharp words to a lover. Some 15 percent of the U.S. workforce labors through these early morning hours, and the schedule is hard on their bodies. Shift work can cause ailments ranging from high cholesterol and high blood pressure to mood disorders, memory lapses, and serious sleep troubles.
Q: What’s so good about sleep?
A: For one thing, it keeps you slender. Most people don’t have a clue how critical sleep is and the weird range of effects on the body when we get too little of it. I certainly didn’t. Depriving ourselves of sleep—getting only 6 hours a night as opposed to 7 or 8—sabotages how we listen, read, calculate, talk, operate machines, drive. Too many nights of lost sleep, and your body changes in ways that look a lot like premature aging. Sleep loss dampens our immune response; it impairs the body’s ability to regulate blood sugar and hormones. It reduces our supply of leptin, the hormone that signals satiety and regulates our energy balance. When we don’t sleep, we feel hungrier, especially for calorie-rich carbs like cake and bread, and eat more. The body treats the loss of a few hours’ sleep like a deficit of 1,000 calories it wants to make up—so it steps up appetite and slows metabolism.
Q: Why did you write this book?
A: I’m in awe of my body—of everyone’s body. I’m fascinated by its incredible complexity and exquisite efficiency, the way it runs itself without a thought from me. But like most people, I had been fairly clueless about the way it works. Then, some years ago, I was hit by a bad case of the flu. When I was recovering, I had this epiphany—it kind of struck me with a bang—that my whole existence was going to come and go in this one body. Wouldn’t it be a good idea to get to know it a little? I thought about going to medical school. But I quickly realized that the one thing I did know about my body is that it needs sleep—which doesn’t fit well with the round-the-clock schedule of doctors in our society. So I decided to tackle the topic as a writer. It’s a great time to do so. There’s a flood of wonderful new information about the body gleaned only in the last few years, thanks in part to new technology for imaging the body and understanding its genes and cells.
Q: What was the most surprising thing you learned about the body in writing this book?
A: There are so many surprising things: that just thinking about an exercise can increase muscle strength; that stress makes us fat; that laughter benefits our blood vessels nearly as much as aerobic activity; that the bacteria and other bugs in our guts help determine our body weight; that a man may be able to tell when a woman is ovulation just by looking at her face. That the body’s 24-hour rhythms profoundly affect the way we feel and how well we function over the course of a day. It’s hard to choose.
Q: What kind of research did you do for the book?
I talked with dozens of scientists and read hundreds of medical and scientific journals. I submitted myself to all kinds of tests and experiments, from tests of my metabolic rate to learn how many calories my body naturally burns in a day—a disappointingly low 1,000 or so—to formal experiments: a study of memory at the University of Virginia, and one at Harvard about how efficient your body is when it walks and runs. For that one, I was wired up with an uncomfortable hair-shirt of pressure sensors and muscle sensors and had silver foam balls glued to my joints (acted as infrared reflectors for three video cameras mapping in 3-D space the locations of my limbs) as I walked and ran on a treadmill.
Q: Where did the title come from?
A: I have my wonderful book designer, Martha Kennedy, to thank for this. It’s the title of a King Crimson song released in 1995. I love the title because it suggests the rhythms and cycles of daily life. But if I were to list the words in order of priority—apologies to my husband—it would have to be a toss-up between eating and sleeping.
Q: Did writing this book change the way you view your own body or the way you shape your days?
A: Yes, in many ways. I’m now far more conscious of my body’s cycles—the ups and downs of body temperature, stress hormones, alertness—and how these things affect the way I operate. I’m much more attuned to the importance of timing in my daily activities, from when I eat my biggest meal or when I take medications to when I schedule important meetings or presentations. I’m also far more respectful of my body’s needs, from regular exercise to frequent laughter. I know I need to get plenty of natural light every day to align my circadian clock with seasonal shifts in day-length. (I try to get outside in the early mornings and to spend at least an hour a day in natural sunlight.) I try to get exercise every day—especially outdoor exercise—because I know it’s good not only for my body but for my brain. Above all, I have new-found respect for the body’s need for sleep. Not for nothing do we spend a third of our hours in slumber. (I try for at least 7 hours/night and insist on 8 to 10 hours for my teenage girls.) We live in a world where people brag about how little sleep they need. Now I know it’s crazy to cheat your body of sleep, and even crazier to ask young doctors to make medical decisions while they’re sleep-deprived!