Although daylight-saving time was sold politically as an energy-conservation measure, it does no such thing. Studies conducted in Indiana prior to 2006, when that state operated under three different time regimes, show either no difference in energy consumption or a small increase in power usage during the months after clocks were moved one hour ahead.

The annual ritual of springing forward and falling back thus possibly produces no energy savings and may be counterproductive. It also requires those who live in places where daylight-saving time is observed to waste time twice a year adjusting their clocks and watches.

Yet the costs of switching between daylight-saving and standard time go far beyond the hassles of “losing” an hour in the springtime and “gaining” it back in the fall.

I am not a doctor and I do not play one on TV, but the medical profession — as Dr. Osvaldo Bustos of George Washington University's School of Medicine pointed out to me recently — has known for years that shifting time forward or backward has negative, and possibly deadly, health consequences.

A Swedish study published in The New England Journal of Medicine on Oct. 30, 2008, reports increases in the incidence of myocardial infarction (heart attack) after the beginning of daylight-saving time and the subsequent return to standard time. Depending on whether the shift occurred in the fall or spring, men and women were found to vary in the extent to which their heart attack risks were increased, but the study's authors concluded from the clinical evidence that time change triggered more myocardial infarctions in the two groups overall than they would have suffered otherwise.

The underlying causal mechanism has to do with how the hypothalamus regulates humankind's circadian rhythms. When the “clock” that governs those rhythms is abruptly shifted one hour forward or backward, it struggles to adjust the body's internal physical, chemical, electrical, hormonal and immunological environment to the new conditions.

Most people, fortunately, are made aware of the hypothalamus' attempts to cope by having to put up with feeling groggy and being less productive at work or at home for a few days only. Others, however, apparently experience more serious effects, including having a heart attack, from which, it is to be hoped, most recover.

It would be cold comfort were only a small fraction of the population subject to the untoward health consequences of time shifting. That is because, as the Swedish study notes, more than 1.5 billion people around the globe are exposed to the transitions demanded of them at the beginning and ending of daylight-saving time. Many of the companies located overseas that provide technical support or other services to U.S. businesses operate on New York time. Workers in Manila, Mumbai and elsewhere therefore must adjust their clocks twice a year even if their own nations have not officially adopted the institution of what in some places is called summer time.

When a small elevated risk of heart attack per person is multiplied by the 1.5 billion people exposed to that risk, you realize that many men and women suffer debilitating heart attacks and death every time we spring forward and fall back.

Adding to the bill, some students of daylight-saving time suggest that accidents involving pedestrians spike immediately after the return to standard time as well, because drivers have not yet adjusted to commuting home in the dark.

There are few, if any, measurable benefits from switching to daylight-saving time in the spring and back to standard time at the end of October. But time shifting imposes some very real costs.

Those costs, we now suspect, are not limited to feeling out of sorts temporarily or investing effort in adjusting clocks rather than doing something more enjoyable or productive. The twice-a-year ritual of time travel actually kills.

Shughart is the F.A.P. Barnard Distinguished Professor of Economics at the University of Mississippi and a senior fellow at The Independent Institute in Oakland, Calif.