Shelby Harris is the director of the Behavioral Sleep Medicine Program of the Sleep-Wake Disorders Center at Montefiore Medical Center and an assistant professor of neurology and psychiatry at the Albert Einstein College of Medicine.

The human circadian clock is supposed to gradually adjust over the course of a season, with sleep and wake times slowly changing in response to the changing length and intensity of sunlight. But each year daylight saving time begins, we lose one hour of sleep – shifting our internal clocks faster than nature intended. One hour may not seem extreme, but we can’t reset our circadian rhythms as easily as we change the time on the microwave.

The human body does not readily or easily adapt to jarring changes in the alarm clock.

Scientists have connected a number of health consequences with the start of daylight saving time. Swedish researchers reported a 5 percent greater risk of heart attack in the three days immediately after the spring time change. Risk of heart attack is generally highest in the early morning year-round, but “springing forward” causes a sharp increase in early morning heart attack rates because of the earlier-than-usual wake times when the body’s cardiovascular state is least steady and more vulnerable to stress. When daylight saving time ends in the fall and we gain an hour of sleep, incidence of heart attack briefly falls below normal.

Even one hour of lost sleep affects many areas of functioning – decreasing motor function, memory and mood. After the spring time change, traffic accidents are more frequent and workplace injuries are more common. In the first few weeks after the “fall back,” suicide rates sharply increase. However, fewer vehicular accidents occur during daylight saving time, when the daylight hours are extended.

Considering productivity, energy use and many other societal factors, the pros and cons of daylight saving time are many and varied. But it’s clear that the human body does not readily or easily adapt to jarring changes in the alarm clock. We could keep daylight saving time or not, but if health and safety are the deciding factors, we should stop switching back and forth.



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