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Does Daylight Saving Time Cause Heart Attacks?


Updated October 27, 2011

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Now that we're about to say goodbye to daylight saving time (DST) for another six months, perhaps (according to researchers reporting in the New England Journal of Medicine), we'd be better off saying goodbye forever.

These investigators reported an association between heart attacks (also called myocardial infarction) and switching to DST in the spring. Their report indicates that heart attacks among Swedish men and women increase by 5% during the first few weekdays after the clocks are advanced one hour in the spring for DST. This effect is partially reversed in the fall, when the incidence of heart attacks drops slightly after clocks are set back to standard time.

Does this mean that DST time is a public menace and should be abandoned? No. (As an Ohio farmer once explained to me, his corn crop really appreciates the extra hour of sunlight provided by DST - and it's hard to argue with logic like that.)

What this report actually means is that there is a link between sleep deprivation and cardiovascular problems. We've known about this link for a long time. But typically, sleep deprivation - an extremely common and almost "normal" phenomenon in modern society - occurs randomly among the population. In contrast, when we begin DST in the spring, we are systematically coordinating a night of sleep deprivation (and a few days of sleep-cycle readjustment) for a few billion people around the world simultaneously, which gives us an opportunity to observe and measure the effects of sleep deprivation across a large number of people. When we do so, we can see that sleep deprivation, in general, poses health risks.

So this study doesn't so much indicate that DST is a bad idea, but rather, points out that even a relatively minor sleep-disruptive event such as this one can have health consequences. What this study really means is that we should all pay more attention to our sleep cycles, do our best to get enough sleep, and try to avoid unnecessary disruptions in our sleep patterns.

But for the sake of our corn crops, we should probably leave DST alone.


Janszky I, Ljung R. Shifts to and from daylight saving time and incidence of myocardial infarction. N Engl J Med 2008; 359:1966-1967.

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