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HOW COME? Daylight saving time and its effect

Does switching to daylight saving time have any effect on the body? asks Anneliese Tham Magrograssi, a reader in Gussago, Italy.

Next Sunday, it's that time again. The time we'll all be "springing forward" -- in the middle of the night.

Much of the world fiddles with clocks and wristwatches in spring and fall, but every country does it on their own schedule. Which adds an extra level of circadian confusion to travelers, already jet-lagged by jumping time zones.

What's the point of moving clocks ahead an hour in spring, only to set them back to "real" time in the fall? From spring to fall, when daylight hours are longer than in winter, daylight saving time shifts an hour of daylight from the morning to the evening. Research shows a drop in sedentary TV watching and an uptick in exercise when daylight extends an hour in the evening. We use less electricity, and statistics show that some crimes drop.

But not all the effects of daylight saving time are positive. Many people suddenly find themselves getting up in darkness to go to work or school. And then there's the sleep disruption, which sometimes extends for many days. Several studies have shown a spike in heart attacks in the first days of DST in the spring, with a similar drop after clocks are set back in the fall.

If DST does have some unhealthy consequences, scientists say it's not surprising. As we orbit the sun on our tilted planet, the sun's position in the sky changes over the seasons. And as we observe the shifting light, our body clock resets itself, day by day. When we add the hour change to the seasonal changes our internal clocks undergo in spring and fall, researchers say the effect can be "drastic."

One German scientist compared it to abruptly moving the population of Germany to sunny Morocco in the spring, and whisking them back in the fall. His research found that people adjusted their sleep and activity most easily during the fall transition. In spring, more people -- especially night owls -- had a hard time adjusting to the change.

Scientists say that keeping our built-in clock attuned to nature's has an impact on health. Studies show that when our normal circadian rhythms are altered -- say, by shift work -- our risk of cardiovascular disease, cancer, diabetes and mood changes, including depression, may rise.

So whether we are operating on standard time or DST, researchers say we should try to get more sunlight, especially in the morning, "entraining" our body clock to the changing light.

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