We’ve long known that circadian rhythm—the way our body functions line up with day and night—dictates our ideal sleep-wake schedule. Now, scientists are finding that almost every system runs on a 24-hour clock. That makes it possible to dial in on the ideal schedule for things like eating, exercise, and even taking medication. Time it right and it could mean the difference between skating by and working at maximum efficiency.
“Think of the master clock in your brain as an orchestra conductor and the clocks in the rest of your body as the different sections of that orchestra,” says Courtney Peterson, a researcher at the University of Alabama at Birmingham.
Experts have long suspected that humans are bound to an internal clock. It is something that they discovered, in part, by looking at the plethora of health issues that befall shift workers, long-haul truckers, and others who work through the night and sleep during the day. For instance, those workers have an increased risk of certain types of cancer, cardiovascular disease, obesity, and depression.
Here’s what happens: When morning light hits our eyes, it activates a certain protein, which, in turn, sends a signal to the brain’s hypothalamus that it’s time to get going. The brain releases hormones throughout the body that wake up all the systems. Body temperature rises, blood pressure goes up, and by midmorning you’re on high alert. The reverse happens when the sun goes down. For most, seven to nine hours of continuous sleep (going to bed between 10 p.m. and midnight and waking in the 6 a.m. to 8 a.m. range) is optimal.
So, now you’re awake, and it’s time to get going. It’s been a while since your last meal, and your body wants to get fueled up first thing in the morning, so if you’re a breakfast-skipper, you may want to rethink. It appears that our metabolic circadian rhythm is set up so that muscle cells are most sensitive to insulin—the hormone regulating blood sugar—earlier in the day. Breakfast will probably burn as energy, while a late dinner will store as fat.
In a small pilot study of prediabetic men, those who followed intermittent fasting—eating all three meals in a six-hour period (meaning dinner ended by 3 p.m.)—after five weeks had reduced their blood pressure by 11 points, on average, and increased their insulin sensitivity, which could help with weight loss.
It comes down to resource distribution. Your body devotes a lot of energy and attention to digestion, which is why you’d never go for a run right after eating a big meal. Putting more time between dinner and bedtime means your body can focus on restorative sleep and repairing tissue, says Satchin Panda, a biologist at the Salk Institute and author of The Circadian Code. Since eating dinner mid-day is impractical, Panda suggests keeping meals in a 12-hour window or less, if you can: breakfast at 7 a.m. and dinner by 7 p.m.
Get on the right schedule and your body puts those calories to good use. Peterson’s study in the journal Cell Metabolism suggests that eating per your circadian clock reduces the amount of metabolic “garbage” that builds up in cells, what biologists call oxidative stress. Too much oxidative stress can cause inflammation, which is a driver of disease.
As for exercise, late afternoon is ideal for circadian synchronicity. A review of research from the University of Bergen in Norway finds that performance usually peaks midday and later. For instance, swimmers are faster in the evening even if they’re used to hitting the pool first thing in the morning. And if you’re looking to PR a strength and power move, like a back squat or broad jump, you get better at those as the day goes on (though exercising at night can prevent some people from falling asleep easily, making this bit of intel a catch-22).
And scientists are only scratching the surface. For instance, animal and human studies reveal that even the immune system has a clock. It may help explain why people have more heart attacks in the morning, or why the achiness from arthritis decreases as the day goes on. And it might be why shift workers, whose sleep-wake schedules are constantly changing, have a greater risk of certain autoimmune diseases than the rest of the population.
Uncovering the immune system’s clock has exciting applications. It could mean that vaccines like the flu shot could be more effective by timing them. “The impact is underappreciated,” says Paul Frenette, M.D., a medicine and stem-cell researcher at the Albert Einstein College of Medicine in New York. “There could be significant benefits to chronotherapy— administering certain drugs and therapies, such as chemotherapy, at the right time of day.”
So go with the circadian flow. Get up with the sun or not too long after. And throw open the shades or go out for a run. Exposure to outdoor light boosts your mood, protects against depression, and sets you up for the early meal plan.
Obviously, a late dinner or tickets to a basketball game can get in the way of sticking to your optimal circadian schedule. To get a solid night’s sleep, below are a few scientifically backed methods for maximizing shut- eye—without a prescription.
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