Is Daylight Saving Time Responsible for Heart Attacks?

Last updated: November 18, 2019

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About 25 countries observe Daylight Saving Time (DST) – moving the clock one hour forward in summer and one hour back in the fall so that we make use of the daylight in summer months. As much as you may be happy for the extra hour in fall, you’ll be regretting it in spring when it’s taken away from you. Many of us don’t know that DST doesn’t only make you feel miserable; it also makes your body miserable and the most drastic example of this is the increased incidence of heart attacks in the first couple of days after the spring DST change.

DST increases heart attacks

Sleep and heart health are closely related. Sleep helps lower the blood pressure and keep the C-reactive protein (which is linked to heart attacks) in order. Occasional naps can lower the risk of suffering cardiac infarction while some of the numerous consequences of continuous poor sleep include hypertension (increased blood pressure) and cardiovascular diseases.

But what does one-hour change have to do with heart risks? According to a Swedish 2008 study, there’s a 24% increase in heart attacks following the spring change and 21% drop in fall. 

This tells us that a one-hour clock shift makes a huge difference when it comes to our health and our lives.

The study was conducted over a period of twenty years, from 1987 to 2006 which confirms that this is a serious health risk happening worldwide every single year. We should at least give it some thought and prepare for it every spring.

Heart attacks in the first week after the clock shift. Source: Shifts to and from Daylight Saving Time and Incidence of Myocardial Infarction. The New England Journal of Medicine

The chart above tells us that the first three days are the ‘deadliest’ with Tuesdays being somewhat more dangerous than other days after the spring change. Let’s say a person wakes up on Monday, their body is stressed out with the change and they spend the rest of the day sleep-deprived, accumulating more stress. That night they go to sleep at their usual (late) time because their circadian rhythm is still used to going to bed by the ‘old clock’. The next morning there’s another blow to the heart and as the cardiovascular system and the entire body didn’t get the chance to recover, it finally ends up with a cardiac arrest.

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Who should be worried about the spring clock shift?

The study showed that the majority of people were younger than 65 (that is, working age people) and the incidence of cardiac infarction was slightly more pronounced in women, whereas the fall shift showed slightly more beneficial for men.

Anyone operating a motor vehicle should take extra caution after a DST shift. Both an American and a Canadian study show that immediately after spring DST change there’s an increase in fatal traffic accidents due to sleepy drivers.

What happens in the body on DST that causes a heart attack?

Sleep deprivation has a strong link with C-reactive protein (CRP), a substance whose concentration can predict future cardiovascular problems. 

C-reactive protein is a marker of inflammation, that is, your liver produces CRP and releases it into the bloodstream as a reaction to inflammation in the body. It could mean there’s an inflammation in the arteries, which further means there could be a higher risk of a heart attack. 

One study examined how CRP concentration changed in response to partial and total sleep deprivation. Scientists found that CRP is increased during both – partial (short sleep) and total (no sleep) deprivation. Those who took part in the partial deprivation experiment also had an increased heart rate while those who had total sleep deprivation had elevated systolic blood pressure.

This means that short or no sleep increases inflammation and negatively affects heart rate and blood pressure, all of which are bad for your heart health.

You don’t like Mondays? They don’t like you either

It seems that there are more heart attacks on Mondays than on other days, regardless of DST – one study looked at this problem and found that working, non-hospitalized people are in fact more likely to suffer from a heart attack on a Monday.

However, this has nothing to do with you going back to work. It is rather most likely linked to our weekend behavior which counters human physiology and healthy rhythm. Those who stay up late on weekends and then sleep in, or simply try to ‘make up’ sleep lost over the week are not doing themselves a favor. This disrupts their body rhythm and makes it hard and unnecessarily stressful to wake up on Monday. Keeping up with bad sleeping habits for years will sooner or later result in something ugly.

If we combine this weekend behavior/Monday problems with an hour less due to DST, we get a recipe for a likely disaster.

How to prepare for Daylight Saving Time and stay safe? 

First of all, mark your calendar. By this, we mean to make sure you get a notification a few days before the DST shift. That’s when you can start going to bed and getting up a bit earlier every day. You can start with 10 minutes early, the next day 10 minutes even earlier, and so on. This way you won’t feel the consequences of DST.

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This is not so simple for those ‘weekend sleepers’ because they don’t have a neat sleep schedule and they are in a much bigger problem.

To keep your mind and body healthy, follow the basic rules of sleep hygiene:

  • Make a sleep schedule and stick to it. It doesn’t matter if it’s the weekend, workday or holiday – if your sleep time is 11pm-7am do your best to protect it! It could save your life.
  • Avoid LED and screen light late in the evening so that you can fall and stay asleep easily.
  • No caffeine after 2pm and no alcohol before bed. They negatively affect your sleep quality and quantity.
  • Sleep in a dark and cool room.

Additional Resources

  1. Shifts to and from Daylight Saving Time and Incidence of Myocardial Infarction https://www.nejm.org/doi/full/10.1056/NEJMc0807104
  2. Excess cardiac mortality on Monday: the importance of gender, age and hospitalisation https://link.springer.com/article/10.1007/s10654-004-6594-4
  3. Effect of sleep loss on C-Reactive protein, an inflammatory marker of cardiovascular risk http://www.onlinejacc.org/content/43/4/678.abstract
  4. The Human Circadian Clock’s Seasonal Adjustment Is Disrupted by Daylight Saving Time https://www.sciencedirect.com/science/article/pii/S0960982207020866
  5. Transition to daylight saving time reduces sleep duration plus sleep efficiency of the deprived sleep https://www.sciencedirect.com/science/article/abs/pii/S0304394006007038?via%3Dihub
  6. Fatal accidents following changes in daylight savings time: the American experience https://www.sciencedirect.com/science/article/abs/pii/S1389945700000320
  7. Daylight Savings Time and Traffic Accidents https://www.nejm.org/doi/full/10.1056/NEJM199604043341416 
  8. Changing to Daylight Saving Time Cuts Into Sleep and Increases Workplace Injuries https://www.apa.org/pubs/journals/releases/apl9451317.pdf
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