How Daylight Saving Time is hurting your heart

by Carolyn Thomas   ♥  @HeartSisters

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 you squint open one sleepy eye at 6 a.m. tomorrow morning, your body will feel like it’s really only 5 a.m. Ouch!  And a number of studies suggest that the rates of acute myocardial infarction (MI or heart attack) are significantly increased immediately after this transition to Daylight Saving Time every spring.

So good luck at successfully getting through that transition this year.   .

One such study published in the New England Journal of Medicine, for example, found that the negative effects of this spring transition were more pronounced in women than in men, while the autumn effect seems to be more pronounced in men than in women(1).  

This month, Dr. Lorrie Kirshenbaum, Director of the Institute of Cardiovascular Sciences at St. Boniface Hospital in Winnipeg, warned:

“Recent work we’ve been doing is showing a strong link that further substantiates the very real and detrimental effects of Daylight Saving Time on cardiovascular health, increasing the risk of heart attacks and heart disease.”

These effects may be especially problematic if you’re a shift worker (many of whom are female healthcare professionals) who must adjust internal clocks to work schedules “leading to sleep deprivation, fatigue and decreased cognitive function.”  

The negative effects of the time change are not limited to heart issues, as the Winnipeg researchers warn, but may also apply overall to physical and mental health, including increased risks for diabetes, obesity, heart disease, depression and even some forms of cancer.

One plausible explanation for research findings like these is the known adverse effect of sleep deprivation on our overall heart health in general. See also: Are Your Sleep Problems Linked to Increased Heart Disease Risk?

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

But two other possibilities may help to explain this increased cardiac 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 also have a clock, and the immune response depends greatly on the time of day. In animal studies, when a mouse is given a dose of an endotoxin that elicits strong immune responses in animals, the mouse’s survival depends upon the time of day they were given this endotoxin.

“Control animals that were not subjected to a phased advance  like a time change survived, while mice experiencing a phased advance did not, showing how an acute time change can be detrimental to the immune system response.”

A study from the University of Michigan supported those possibilities.(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 compared to previous weeks. Conversely, the Tuesday following the autumn time changes was associated with a 21% reduction. No other day of the week  following the two Daylight Saving Time changes demonstrated such significant associations.

And let’s consider Mondays for a moment.

A Dutch study(2) reported in the European Journal of Epidemiology called Excess Cardiac Mortality on Monday warned that Monday is the day of the week associated with the highest risk of acute myocardial infarction anyway – with or without a time change – likely due to 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 compared to under-65s(1) – because retired people generally don’t need to set their alarm clocks and rush off to another start of a busy workday on Monday morning any longer?  I’ve personally found this to be very true – because now Monday is the day I get to meet up with one of my oldest friends for one of our wonderful Monday morning walks together – and no alarm clock is ever required!

Another possibility that there is a sleep-related component in this higher incidence of myocardial infarction on Mondays 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 that transition allows for additional sleeping in then.

In the spring, both sleep experts and motor vehicle organizations caution that darker mornings pose health risks and can heighten the threat of driver-related accidents on the road.

Whose bright idea was this?

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 American 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 regions, including other parts of Europe, Canada and the United States, followed suit during the First World War. 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 could help make people become more physically active.”

So until our country decides to heed warnings from researchers like Dr. Lorrie Kirshenbaum to end this time change practice, please try to enjoy those brighter after-dinner evenings – and catch up on some sleep this week if you canOne way to manage the time change, as suggested by Mayo Clinic sleep specialist Dr. Rachel Ziegler, is to go to bed 15 minutes earlier than usual in each of the days ahead, increasing that bedtime by 15 minutes every couple of nights.


(1) Shifts to and from Daylight Saving Time and Incidence of Myocardial Infarction. N Engl J Med; 359:1966-1968 October 30, 2008
(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 generally affect you?

8 thoughts on “How Daylight Saving Time is hurting your heart

  1. Pingback: RN in NYC
  2. Seeing as we now have electrical lights and other appliances, and most people aren’t farming but living in urban areas, there is no need to change the clocks so we can chase the light. I find the actual change difficult and my friends have all heard me crab “I wish they would just pick one and stay with it”.

    It was interesting to read one of the above comments about teenagers and sleep. All my daughters were swimmers and practice started at 5am 6 days per week. All that meant was that homework was done throughout the day and they went to bed quite early. No issues. (Keep in mind I was the chauffeur and then went straight to work after I dropped them off after practice in the mornings. The things we do for our kids!)

    Too many teenagers stay up too late and so they can’t get up in the mornings and are functioning on very little sleep.

    Getting back to the topic at hand, in my opinion it really doesn’t matter to me whether we have daylight savings or standard time. I absolutely hate the change and that is what makes this whole process difficult.

    We should all be like Saskatchewan and not change the clocks – ever!

    Liked by 1 person

    1. Yes, that’s what the research suggests too – it’s the time CHANGE that hurts us. I love your point about early bedtimes if you have an early wake-up next morning (time change or no time change, makes sense!)

      I suspect most teenagers are chronically sleep-deprived. My son Ben in his teens was a night owl who struggled every morning when he had to get up and dressed for school. Yet those “lights out” decisions are all self-inflicted!

      Bless you for your heroism in being your daughters’ chauffeur all those years!

      YES, we should ALL be more like Saskatchewan! 🙂


  3. I am very scared we will move to permanent daylight savings! I have no problem with dropping the spring ahead/fall back change – but studies on sleep suggest it is best to stay in the non-daylight savings zone.

    After all, here in Canada, permanent daylight savings makes little difference in summer if it means we lose daylight at 9.30pm instead of 10.30pm compared to people closer to the equator where it can mean a sunset at 8pm instead of 7pm.

    But it means something significant if we are not seeing daylight until 9am in the winter mornings (for those that live just north of the US border)! Further north, I have a friend in the Yukon who despairs of winter because sunrise at 11 am is depressing, and it is driving people away from the territory every winter because they can’t stand half the day being in darkness. Business doesn’t adjust for such long darkness in the morning!

    Liked by 1 person

    1. I agree – it’s the annual transition from one time change to the next that appears to be most concerning to researchers. I’m all for whichever plan offers the most sunlight and the most common sense to avoid those sudden and abrupt annual changes in our bodies’ ability to adapt.

      I had to laugh at your Yukon friend’s comment. I used to live in Inuvik, north of the Arctic circle near the tree line, beyond which is just tundra, much farther north than where your friend lives, where we didn’t see actual “sunrise” until spring started. Winter is indeed quite dark in the Arctic but the transition is gradual, and the flip side of that is 24-hour daylight all summer (which is wonderful – picking wild blueberries at midnight!) but it also had us taping layers of newspapers onto bedroom windows to keep the rooms dark enough to sleep. Our famous igloo-shaped church grew the most fantastic veggie garden I’d ever seen (cabbages that were unbelievably jumbo-sized due to that nonstop sunshine day and night most of the summer – a short but very intense growing season). And the town sounded a 9 o’clock siren every evening in summer – which every teenager knew meant time to go home for bed – because if their parents had said “Come home before dark!” (as my own parents said when I was that age growing up near Niagara Falls) – the teens wouldn’t come home until autumn!

      Take care, stay safe, and enjoy the sun. . . . ♥

      Liked by 1 person

  4. I think the topic of daylight saving time is political manipulation. And there is no shortage of weak research.

    Consider, if you will, that all living things have their unique circadian rhythm.

    Raccoons sleep during daylight as they are awake and foraging at night. Cougars seem to prefer to hunt when the hunting is good and nap while waiting.

    Life is complex with competing needs, most of which are related to the wishes of those who have power over others.

    For instance, school districts profit from using a minimal number of buses. One employee per bus starts early to pick up high school students before 7am for a high school start time of 7. Older students walk to school in the dark for most of the year. It’s not safe, and they struggle because their bodies need to be napping. That same bus driver repeats the pick up route before 8 for a 8 am start at middle school. Then repeats their route before 9am for the 9am start at elementary school. So the children are sleep deprived to meet the needs of the school district.

    The community bus administration couldn’t explain why ridership falls off rapidly each Fall and picks up rapidly each Spring. The city transportation board sat in silence trying to make sense of the data. The catering worker asked to speak… and politely explained the spike changes coincided with daylight savings time shifts. No one feels safe waiting for the bus in the dark in our city.

    Humans need sunlight to thrive. Short winter days create emotional stress in everyone, particularly those who cannot get their sun quota because of their schedule. Competing demands cause stress and over time cause a lot of damage to our bodies. We do it to ourselves by continuing relationships with things that are harmful. Bad jobs, bad relationships, bad nutrition, lack of sleep, lack of sunlight and fresh air. Daylight savings time switches are no more stressful than having a sick child or catching a time disrupting flight. It’s annoying for some … and the rest of us just laugh it off over coffee and adapt.

    Ideally, everyone would be happy as my hunting dog who wakes up at dawn, eats three square meals while hunting all day, has good people and dogs in his daily life, then falls into a heavy sleep after the sun sets. He isn’t driven by a mechanical clock and other imposed schedules. His clock and daily rhythm is the life giving sunlight.

    Think hard on these points. Daylight savings time is an imposed schedule to help integrate complex human lives to maximize output during daylight hours. It’s truly not a bad thing!

    Liked by 1 person

    1. Hi Anne – thanks for sharing that perspective! Unlike your hunting dog, my career WAS driven by my bosses’ “mechanical clock and other imposed schedules.” I never did figure out a way to make a living that allowed me to “hunt when the hunting is good and nap while waiting”.

      And there are many cardiac researchers who would argue that the transition to DST is significantly more stressful than catching a single time-disrupting flight.

      DST may be political manipulation, yet many jurisdictions are using the same politics to drop the practice for the reasons mentioned in this post.

      Take care, stay safe out there. . . ♥


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