Is Daylight Saving Time hurting your heart?

by Carolyn Thomas

It’s time once again, heart sisters, for the springtime ritual that welcomes something called Daylight Saving Time. This is not a good time of year if you love to sleep in. When that alarm clock buzzes you wide awake at 6 a.m., your body feels like it’s REALLY only 5 a.m. Ouch! Some studies suggest that the rates of acute myocardial infarction (heart attack) are significantly increased immediately after the transition to Daylight Saving Time every spring.

Good luck at successfully getting through that transition this year.

A study published in the New England Journal of Medicine(1) found that the negative effects of this time transition were consistently more pronounced for people under 65 years of age than for those 65 years of age or older. Research suggests that the effect of the spring transition on the incidence of acute MI, in fact, is somewhat more pronounced in women than in men, while the autumn effect is more pronounced in men than in women.

Why does this happen? One plausible explanation for research findings is the adverse effect of sleep deprivation on our overall cardiovascular health.  See also: Are Your Sleep Problems Linked to Increased Heart Disease Risk?

Some experts estimate that people in Western societies are chronically sleep deprived. The average sleep duration decreased from 9.0 to 7.5 hours during the 20th century.

Two other possibilities may help to explain this increased heart attack risk tied to the Daylight Saving Time change, according to Dr. Martin Young of the Division of Cardiovascular Disease in the University of Alabama at Birmingham, who explained:

1.  Circadian clock “Every cell in the body has its own clock that allows it to anticipate when something is going to happen and prepare for it. When there is a shift in one’s environment, such as springing forward, it takes a while for the cells to readjust.

“It’s comparable to knowing that you have a meeting at 2 p.m. and having time to prepare your presentation instead of being told at the last minute and not being able to prepare.

“The internal clocks in each cell can prepare it for stress or a stimulus. When time moves forward, cell clocks are anticipating another hour to sleep that they won’t get, and the negative impact of the stress worsens; it has a much more detrimental effect on the body.”

2. Immune function:  “Immune cells have a clock, and the immune response depends greatly on the time of day. In animal studies, when a mouse is given a sub-lethal dose of LPS, an endotoxin that elicits strong immune responses in animals, the mouse’s survival depends upon the time of day they were given this endotoxin.

“Mice that were put through a phased advance much like Daylight Saving Time, and then had a challenge to their immune system, died, whereas the control animals that were not subjected to a phased advance survive when given the same dose of LPS, showing how an acute time change can be detrimental to the immune system response.”

A Dutch study(2) reported in the European Journal of Epidemiology called Excess Cardiac Mortality on Monday warns that Monday is the day of the week associated with the highest risk of acute myocardial infarction anyway, with the mental stress of starting a new work week and the increase in activity suggested as an explanation. (Might this also help to explain the lower MI rates after a time change for over-65s, because retired people don’t have to set their alarm clocks for Monday morning any longer?)

UPDATE: A 2014 study from the University of Michigan supported those findings. (3) After adjusting for trend and seasonal effects, the Monday following the spring time change was associated with a 24% increase in daily acute heart attack counts. Conversely, the Tuesday following the autumn time changes was conversely associated with a 21% reduction. No other weekdays in the weeks following Daylight Saving Time changes demonstrated significant associations.

Another possibility that there is another sleep-related component in the excess incidence of acute myocardial infarction on Monday is that bedtimes and wake-up times are usually later on weekend days than on weekdays. These earlier wake-up times on the first workday of the week and the consequent minor sleep deprivation have been hypothesized to have an adverse cardiovascular effect in some people. This effect would be less pronounced with the transition out of daylight saving time in the fall, since it allows for additional sleep then.

Daylight Saving Time was first enacted in Germany in 1915. Because the sun shone for a time while most people were still asleep in the morning, it was thought that light could be better used during the day. The solution was to push the clocks ahead one hour in springtime, forcing people to wake an hour earlier. They would thus expend less energy trying to light their homes, for instance, if time were adjusted to suit their daily patterns.

When the days started getting shorter in the fall and people awoke to increasing darkness, the clocks were turned back an hour to get more light in the morning.

In fact, the idea of Daylight Saving Time had been batted around for a long time.  Benjamin Franklin suggested the idea more than once in the 1770s while he was an emissary to France. But it wasn’t until more than a century later that the idea of Daylight Saving Time was taken seriously. The reason: energy conservation. Britain quickly followed Germany and instituted British Summer Time in 1916.

Several areas, including other parts of Europe, Canada and the United States, followed suit during the First World War. In most cases, daylight time ended with the armistice. Most — but not all — jurisdictions in Canada and the U.S. have been moving their clocks ahead by one hour on the second Sunday in March and back by one hour on the first Sunday in November.

But there may be a glimmer of good news this spring, according to Consumer Reports Health:

“On the plus side, the extra hour of sunlight can be welcome relief for people who suffer from seasonal affective disorder. And it might motivate people to spend more time outdoors after work, when people tend to have more free time, which theoretically anyway could help make people be more physically active.”

So try to catch up on some sleep this week if you can.


(1) Shifts to and from Daylight Saving Time and Incidence of Myocardial Infarction. N Engl J Med 2008; 359:1966-1968 October 30, 2008DOI: 10.1056/NEJMc0807104
(2) A Meta-analysis of excess cardiac mortality on Monday. European Journal of Epidemiology. May 2005, Volume 20, Issue 5, pp 401-406.


(3) Sandhu A, Seth M, Gurm HS. “Daylight savings time and myocardial infarction”,


.Q:  How does the time change affect you?


3 thoughts on “Is Daylight Saving Time hurting your heart?

  1. I’m over 65 and retired, but I still seem to suffer at this time of year because of DST, even though I no longer have to set my early morning alarm any more. Youd think it wouldn’t matter – maybe its all in my head? 😉


  2. DST is sure hurting MY heart, brain, back, eyes, legs, you name it. It seems to take me weeks after the time change to begin feeling like halfways normal again. ….yawn….. 😉


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