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Circadian Rhythm

Why So Many People Hate Daylight Saving Time

Switching the clock back and forth is bad for the body’s circadian chronometer.

Key points

  • Biology dictates leaving the clock on standard time, not an hour ahead.
  • Our bodily clock synchronizes daily to the changing duration of light and dark, giving us our circadian rhythm.
  • Give yourself as much light as possible on awakening. The body sets its rhythm in response to natural short-wave light.

Over half the U.S. population hates setting the clock forward each spring. Well, not even spring, which doesn’t happen yet this year until Monday, March 20. By then, our brains will have spent only 125 days, merely one-third of a year, exposed to standard time: between November 6 and March 11.

Our bodily clock in the brain synchronizes itself daily to the changing duration of light and dark, giving us our circadian rhythm (from the Latin circa dies = “approximately one day”). Changing life’s mechanical clocks wreaks havoc with the biological timekeeper in our brains.

Yet the “Sunshine Protection Act” proposed by Senator Marco Rubio and colleagues aims to make daylight saving time permanent. They get it backward, however: Standard time, not daylight saving, is most in tune with human biology.

The Senators mistakenly base their preference on economics. They imagine an extra hour of evening sunlight year-round would be good for business. But daylight saving time doesn’t increase the amount of daylight. That would be physically impossible unless we could stop the earth from rotating. It merely time-shifts it, and for many people doing so causes nothing but stress and aggravation.

According to a University of Chicago poll, 75 percent of Americans would prefer to end the practice of switching the clocks twice a year. After changing to daylight saving time, the American Academy of Sleep Medicine found that nearly 60 percent of American adults feel drained and inefficient for a week or more. The Academy raises ample cause for concern: your body knows what time it’s supposed to be, and when government tampers with it, your health can suffer, sometimes in deadly ways.

Take the simple case of jet lag, which happens because our inborn circadian rhythm adapts sluggishly to a change in time zones. It takes the body’s clock about two days to adjust to the local dark-light cycle of your new destination. In the case of daylight saving time, however, mechanical clock time changes while the dark-light cycle does not, and the body may never adjust to it physically.

Standard time comports with natural time when the sun directly overhead equals noon, no matter where you are. Daylight saving essentially puts us in another time zone without changing the day-night cycle. This misalignment asks the circadian clock to change our physiological rhythms and to do things at times that are not biologically appropriate.

Individuals may lose up to 19 minutes of sleep per night until standard time returns, which is hardly the only untoward consequence. Multiple studies confirm increased physical injuries, car collisions, heart attacks, strokes, miscarriages, and depression.

Studies have found a 24 percent increase in the risk of having a heart attack the day after moving clocks forward and a 5 to 15 percent increase in the risk of having a heart attack in the week after shifting to daylight saving. The Academy calls it “a preventable cause of cardiac injury” and speculates that “the risk stays elevated throughout the months we stay on daylight-saving time.” The increased risk of having a stroke may last even longer.

Politicians shouldn’t be playing with our health for the sake of commerce.

The springtime clock change affects some people more than others. Night owls who habitually stay up late may have it the roughest, while even morning larks can turn grumpy, listless, and generally out of kilter for a week or two after pushing the clock forward. “Spring forward” fights our ingrained circadian rhythm, and its untoward effects are most noticeable in individuals who don’t get enough sleep, to begin with. Some individuals have a hard time concentrating and feel the need to nap.

The American Academy of Sleep Medicine recommends doing away with our current twice-yearly time changes “in favor of a fixed, national, year-round standard time.” #StandardTime is also endorsed by the American Academy of Neurology, the National Safety Council, school and parental associations, and authorities who study chronobiology. Failing that, the education arm of the Academy recommends arming yourself by getting at least seven hours a night for two to three days before and after the switchover.

Then, on Sunday morning, go outside and expose yourself to morning sunlight. This will help to reset your internal clock.

More from Richard E. Cytowic M.D.
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