Monday, 12 March 2012

Is Daylight Savings costing us lives?

Next week, on Sunday March 25th, the clocks will spring forward an hour for Daylight Savings. Other than having an hour less in bed, and feeling a bit more sleepy in the week, can this have any other significant effect on our body clock? Can it cause you to have a heart attack?

Research published this year has looked at the effect of Daylight Savings on the number of people suffering acute myocardial infarctions (heart attacks) in Sweden [1].

Blood pressure is a component of the body clock, dipping low at night naturally. Heart attacks are far more likely to occur in the morning when your blood pressure is rising. Can altering the timing of the body clock by just one hour have such a profound effect on your heart as to cause a heart attack?

Heart attacks are linked to the body clock, being more likely to occur in the morning  © Grewlike

In 2008 the group showed that in the week following the transition into Daylight Savings the number of people going into hospital with heart attacks did increase [2]. In that study they analysed hospital admissions over 19 years, comparing the fortnight before with the fortnight afterwards.

In their latest study they repeated the analysis on data collected from 2007 from 74 hospitals, covering 95% of the coronary care admissions in Sweden. This data was more detailed, so they could find out who were more at risk.

As well as age and gender, there was information on other heart attack indicators such as cholesterol levels, BMI, smoking history, diabetes, high blood pressure, history of heart problems, other heart attacks etc.

When they analysed this new data, they observed the overall increase in heart attacks again. There were higher rates of heart attacks in the week following Daylight Savings. The increase measured was smaller than the first study, however still significant (and therefore still a risk).

More heart attacks occur in the week after entering Daylight Savings Time (DST) in the Spring © Janszky, 2008 

Those at higher risk in this Spring week included all those on preventative medication, including aspirin, calcium channel blockers and statins.

Remarkably, those who had a high cholesterol and high triglyceride (fat) levels seemed to have less heart attacks. This was unexpected, but the researchers point out that they have no information on the sleeping and activity levels of this group.

It could be those who are protected in this week are more sedentary, sleep more, and become less sleep deprived than the rest of the population. Further information on the link between sleep, the body clock and heart attacks could determine what advice can be given to those vulnerable of having a heart attack.

With 1.5 billion people (close to a fifth of the world's population) being influenced by Daylight Savings, a small increase in the number of heart attacks can have large ramifications. Governments, scientists and society really need to investigate their motives for having daylight savings.

In the meanwhile, take it easy next week!

Enjoy this blog post? Check out: Double Summertime: Double trouble? and Using time of day to reduce heart damage in breast cancer treatment

[1] Janszky, I., et al. (2012). Daylight saving time shifts and incidence of acute myocardial infarction - Swedish Register of Information and Knowledge About Swedish Heart Intensive Care Admissions (RIKS-HIA). Sleep medicine. Elsevier B.V. doi:10.1016/j.sleep.2011.07.019

[2] Janszky, I., & Ljung, R. (2008). Shifts to and from daylight saving time and incidence of myocardial infarction. The New England Journal of Medicine, 359(18), 1966-8. doi:10.1056/NEJMc0807104


  1. Is this not a case perhaps of:

    "We have noticed that drownings increase directly in proportion to the number of Ice Creams sold. Therefore eating Ice Cream increases the risk of drowning." When actually, summertime is when people both swim more, and buy more Ice Cream.

    What I am trying to say in a long winded way is that perhaps there is another factor? Eg. More kids around 'cos it's usually half term. (Half term definitely stresses me out more!) Or... something else? :-)

  2. Hi Golddawn,

    Thanks for your comment and it's a really important point to make.

    One thing that I didn't mention was that the Swedish did a second round of analysis excluding Sunday's where Easter had occured, and using data from another Sunday. The increase was already significant, but the effect was larger when Easter was taken out of the equation. As if to say that Easter (and they postulate the more chance for sleep) was helping protect against this rise in heart attacks.

    They also noticed in their first paper that the rate of heart attacks were lower in the Autumn, when people gain an extra hour of sleep. However, they didn't reproduce this result in their second paper, so I didn't go into the detail.

    As there are many countries that are using Daylight Savings and keep a record of hospital admissions, it would be interesting if other countries could replicate these findings. This might rule out cultural factors like half terms.

    This data does complement other research showing negative effects of losing one hour of sleep. For example, a rise in the number of car accidents on the way to work on the Monday.

    Certainly warrants more research/decisions on the benefit of Daylight Savings vs the proposed costs.