DARK AGE THINKING:

Daylight saving time isn't just a benign relic of the 1970s energy crisis. The latest research suggests the time change can be harmful to our health and cost us money.

The effects are most disruptive in the spring and fall, right after the time changes occur. Clocks in the U.S. will spring forward this year on Sunday. Most of Europe moves to daylight saving time two weeks later.

The suffering of the spring time change begins with the loss of an hour of sleep. That might not seem like a big deal, but researchers have found it can be dangerous to mess with sleep schedules. Car accidents, strokes, and heart attacks spike in the days after the March time change. It turns out that judges, sleep deprived by daylight saving, impose harsher sentences.

"Even mild changes to sleep patterns can affect human capital in significant ways," two Cornell University researchers, Lawrence Jin and Nicolas Ziebarth, wrote last year.

Some of the last defenders of daylight saving time have been a cluster of business groups who assume the change helps stimulate consumer spending. That's not true either, according to recent analysis of 380 million bank and credit-card transactions by the JPMorgan Chase Institute.

The study compared Los Angeles with Phoenix in the 30 days after the March and November time changes. Arizona is a natural test case since it's one of the two states, along with Hawaii, that doesn't do daylight saving. In the spring, according to the consumer transaction data, the additional hour of evening daylight in Los Angeles managed to slightly boost card spending per person, compared with that in Phoenix, although by less than 1 percent. That spending uptick is swamped by the negative impact of the November time change, which sees the darkened population of Los Angeles spend 3.5 percent less at local retailers.

After the autumn time change, shoppers made far fewer trips to the store, especially during the week. Grocery stores, discount stores, and other retailers bore the brunt, while restaurants and service businesses were mostly unaffected.

In other words, daylight turns out to be a surprisingly large factor in how often workers stop at stores on their way home from their jobs in the evening. "At the end of the day, it's either dark or light, and (people are) going to make an impulse decision at that point," Diana Farrell, president and chief executive of the JPMorgan Chase Institute.

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