Daylight savings time increases risk of heart attack. Here’s what you can do to avoid one.

heart-attackDid you know that adjusting the clock up by an hour in accordance with daylight savings time increases you chance of a heart attack?

Circadian rhythms are biological cycles that occur in humans, animals, insects, plants, and even bacteria with a period of approximately (circa) one day (diem). These rhythms are determined internally by a part of our hypothalamus and are synchronized perfectly to our 24-hr days by the sun and other cues. This internal clock mediates daily variation in everything from hormone levels, to sleep/wake cycles, feeding behaviour, thermoregulation, to bowel movements and cardiovascular function, among many others.

It is largely due to these predictable circadian rhythms that risk of a myocardial infarction (heart attack) is significantly highest in the morning (by about 40% as compared to other times in the day). Right as we awake, our cardiovascular system is in the most compromised state –systolic blood pressure and heart rate show the largest upward spike in the morning, blood vessels ability to dilate in response to increased blood flow is compromised (relative endothelial dysfunction), blood clots are more likely to form, and the ability to break them up is at its lowest point in the day. Is it any wonder then, that the first snowfall – shoveled early in the morning by people at risk – always leads to a spike in heart attacks?

Interestingly, the 1hr shift experienced by citizens of many countries (most notably Europe and North America) during the fall and spring in accordance with daylight savings time also has a detrimental effect on cardiovascular risk. The problem lies in the fact that our circadian clock takes time to adjust, and it is best adjusted by changes in day/night or light/dark cycles – not simply the adjustment of our watch. Thus, the few mornings after the clock change our internal clocks are at odds with our watches and particularly in the spring – when one hour of sleep is lost, we wake up with our cardiovascular system being in an even more compromised state than normal.

2009 study in the New England Journal of Medicine clearly shows this effect. In the study the authors investigated the number of heart attacks in Sweden the week before and the week after the 1hr clock changes in both the spring and fall. As would be predicted, individuals had an approximately 5% greater risk of having a heart attack immediately after the ‘spring ahead’ clock change compared to the previous week.

The authors rightfully suggest that individuals at risk of cardiovascular complications would be better off changing their clocks more gradually (i.e. by 15 minutes, starting on the Friday before the change). More importantly, avoiding strenuous activity and stress right in the morning may also be a valid suggestion.

An even better strategy from a public health standpoint would be to do away with daylight savings time altogether.


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4 Responses to Daylight savings time increases risk of heart attack. Here’s what you can do to avoid one.

  1. Craig primack md says:

    One of the few things that Arizona does right is not follow the US standard of daylight savings

  2. Dr. V says:

    Hmm. Up here in the north (I’m in Canada), switching to mountain daylight from mountain standard gives us lovely sunlit evenings, which, in my neighborhood at least, are well used for walking and playing volleyball in the sand court down the street and cycling and gardening and generally getting ourselves outside. Possibly the difference is not as noticeable further south, but here it gets dark early — like, 4 — much of the year, and the darkness measurably limits outdoor time. Then in summer the sun comes up at 3 am; few of us are willing or able to meet our soccer teams then! From a public health standpoint, possibly the increased activity and increased exposure to natural settings (even if that means enjoying the urban forest) outweighs the brief increase in MI…

  3. Ian says:

    As I was shoveling my driveway straight out of bed this morning, I felt quite shaky and out of breath. While I’m healthy in the cardiovascular manner, I couldn’t imagine being an “at risk” person and conducting this activity. In addition to day light savings time this morning, maybe I should just be happy to be alive! I made it through a high risk activity at a high risk time of year. :o)

    Great post. I’ve wondered what purpose day light savings time has in our modern world. We no longer need to conserve candles like Benjamin Franklin proposed. There’s a documented increase risk of car accidents. According to a CBC interview this morning, it costs North America over 400 million dollars to switch over. So why do we keep doing this to ourselves? Lets pick a time and stick to it. Better yet, let’s all turn off our alarm clocks and wake up naturally with sunlight – and then see how long we keep our jobs. But it’s worth a shot, our health is on the line!