The Battle of Daylight Saving Time Revisited

Daylight saving time is a mixed blessing. Springing Forward gives us an extra hour of sunlight, but Falling Back takes it away. And this twice-yearly time shift is pretty much universally unpopular. A recent Associated Press poll shows only 12 percent of American adults in favor. Their discontent isn’t just simple annoyance. It mirrors a real physical fact.

The human brain has a clock-like feature called the circadian rhythm that is set by exposure to sunlight and darkness. It follows a 24-hour cycle that determines when we become sleepy and when we’re more alert. Each day, morning light resets the rhythm. By evening, levels of the hormone melatonin begin to surge, triggering drowsiness. As a result—although most Americans would prefer longer light at night— even something as simple as the blue light on the computer or TV screen at bedtime pushes the cycle out of sync.

Because the circadian clock also influences heart rate, blood pressure, stress hormones, and metabolism, some health groups, including the American Medical Association and American Academy of Sleep Medicine, have long urged going back to standard time year-round. Data from Stanford University published last month in the Proceedings of the National Academy of Sciences agree.

The Stanford numbers show that switching twice a year is problematic and that choosing either DST or standard time and sticking with it appears scientifically better.

Even last week’s single-hour change can make hash of sleep schedules because, as the Stanford study notes, your workday still starts at the same time. For proof, the consequences of time switching can be tracked in an increased number of car crashes and heart attacks and, the Stanford study suggests, an estimated 300,000 strokes a year. For some, the problem is Seasonal Affective Disorder (SAD), a type of depression usually linked to the shorter days and less sunlight of fall.

America did try once, in the mid-1970s, to switch to permanent daylight saving time. It was supposed to be a two-year experiment but lasted less than a year because it was so unpopular. Unsurprisingly, standard time comes out ahead because it aligns more with the sun. As Jamie Zeitzer, co-director of the Center for Sleep and Circadian Sciences at Stanford, sums up: “The best way to think about it is as if the central clock were like a conductor of an orchestra and each of the organs were a different instrument. The more light you have earlier in the morning, the more robust your clock is.”

Lost Time Is Never Found Again

Historically speaking, the man who stirred up all this time trouble was Benjamin Franklin, who first proposed clock shifting back in 1784, based on the economic argument that prolonging daylight could reduce the need for pricey candles in the evening. Slightly more than a century later, during World War I, Germany tailored Franklin’s notion to its own needs, becoming the first country to adopt daylight saving in order to conserve fuel by reducing the need for artificial lighting. The United States did the same during World Wars I and II. In 1966, Congress clocked in with a law allowing individual states to decide for themselves. Today only Arizona and Hawaii remain on standard time year-round.

In the end, Chad Orzel, professor of physics and astronomy at Union College and author of A Brief History of Timekeeping, concludes that the change in daylight hours in different seasons is now part of our national culture. “People really like having the long evenings in the summer. The price we pay for that is we have to change the clocks twice a year.”