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Time Change Science: Be Careful Tomorrow!

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Photo by didier burton via the LAist Featured Photos pool on Flickr


Photo by didier burton via the LAist Featured Photos pool on Flickr
Did you remember to move your clocks forward last night? If you live in the United States (as well as many other countries), you did. How will that affect you and other people?

Well, for one thing, you are more likely to suffer a heart attack tomorrow than on any other Monday of the year. Why?

Almost all biochemical, physiological and behavioral functions in any multicellular organism (including humans) fluctuate over the course of a day based on an internal, biological clock, called the circadian rhythm. In the early morning hours, heart rate and blood pressure slowly rise and reach a peak in the morning, at the time when we spontaneously wake up. Then, heart rate and blood pressure level off and slowly rise again throughout the day until reaching their peak in the late afternoon.

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But we don't wake up spontaneously every day; we use alarm clocks. By setting your alarm every day to exactly the same time including on weekends, your circadian system will shift to be in sync with the pattern you've set. The natural increase in heart rate and blood pressure will start earlier, and will prepare you for waking up with your alarm.

But most of us don't use alarm clocks on weekends. So we spend all week resetting our natural biological clocks, but then over the weekend they shift back. And when your alarm clocks goes off on Monday morning, your body won't be prepared anymore.

The alarm - which acts as a stressor - will cause your heart rate and blood pressure to shoot up right away. The sudden shock to the heart can, if it is already damaged, lead to a heart attack.

This explains two facts: (1) more heart attacks happen on Mondays than other day of the week, and (2) heart attacks are more likely to occur in the morning, at the time of waking up, than at any other time during the day.

So what's special about the spring-forward time change Monday?

Your circadian clock shifts about 20 minutes during the weekend. Add to that the fact that your alarm clock will go off an hour earlier than last week. So the natural increases in heart rate and blood pressure will be even further behind tomorrow than after any other weekend - in fact, it will be 80 minutes behind. So the stress of the alarm will be greater, and the immediate stress-related rise in blood pressure and heart rate will be even faster and bigger than any other weekend. So if your heart is already damaged in some way, you stand a greater chance of experiencing a heart attack on the Monday following the spring-forward time change than any other Monday of the year.

Is there good news? Well, sort of. We all have experience staying up all night cramming for an exam, or partying with friends, or taking care of a sick child, or what have you. And that doesn't make you more susceptible to a heart attack. That's because the occasional night or two of reduced sleep isn't a big deal - its part of the human condition and we have adapted to the day-to-day variations in sleep duration. Just don't make a habit of it!

And don't worry: in six months, fall-back time change Monday has the lowest number of heart attacks of any other Monday of the year!

Want to learn more about the internal biological clock and how the daylight savings time change affects your body?