Daylight Saving Time 2012: Why and When Does It End? (3)

Daylight Saving Time: Healthy or Harmful?

For decades advocates of daylight savings have argued that, energy savings or no, daylight saving time boosts health by encouraging active lifestyles—a claim Wolff and colleagues are putting to the test.

"In a nationwide American time-use study, we're clearly seeing that, at the time of daylight saving time extension in the spring, television watching is substantially reduced, and outdoor behaviors like jogging, walking, or going to the park are substantially increased," Wolff said. "That's remarkable, because of course the total amount of daylight in a given day is the same."

But others warn of ill effects.

Till Roenneberg, a chronobiologist at Ludwig-Maximilians University in Munich, Germany, said his studies show that our circadian body clocks—set by light and darkness—never adjust to gaining an "extra" hour of sunlight at the end of the day during daylight saving time.
"The consequence of that is that the majority of the population has drastically decreased productivity, decreased quality of life, increasing susceptibility to illness, and is just plain tired," Roenneberg said.

One reason so many people in the developed world are chronically overtired, he said, is that they suffer from "social jet lag." In other words, their optimal circadian sleep periods are out of whack with their actual sleep schedules.

Shifting daylight from morning to evening only increases this lag, he said.

"Light doesn't do the same things to the body in the morning and the evening. More light in the morning would advance the body clock, and that would be good. But more light in the evening would even further delay the body clock."

Other research hints at even more serious health risks.

A 2008 study in the New England Journal of Medicine concluded that, at least in Sweden, heart attack risks go up in the days just after the spring time change. "The most likely explanation to our findings are disturbed sleep and disruption of biological rhythms," lead author Imre Janszky, of the Karolinska Institute's Department of Public Health Sciences in Stockholm, told National Geographic News via email.

advocate - 拥护者，拥护
substantially - 大体上 
ill effect - 弊害
chronobiologist - 寿命学家   chronobiology 时间生物学，寿命学
Munich - 慕尼黑
circadian - 约24小时周期的  circadian clock 生物钟
adjust to - 习惯
drastically - 彻底地，强烈地
productivity - 生产力
susceptibility - 易感染
plain tired - totally tired
jet lag - 时差    recover from jet lag
optimal - 最适的
whack - 分配，殴打
hint at - 暗讽