Subscribe to Obesity Panacea
Subscribe to Obesity Panacea
Subscribe to Obesity Panacea by mail

'Spring Ahead' to a Heart Attack

Tuesday, March 17, 2009 Posted by Peter Janiszewski, PhD

Did you know that ‘springing ahead’ the clock in accordance with daylight savings time increases you chance of a heart attack?

Yesterday I gave a presentation on circadian rhythms in the graduate neuroendocrinology course that Travis and I are taking. While preparing the presentation, I came across some very interesting research that I decided to share with our readers.

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 bahaviour, 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 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.

A recent 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). Even more importantly, avoiding strenuous activity and stress right in the morning may also be a valid suggestion.


Enjoyed this story? Share it with your friends by clicking the buttons below!

Twitter Facebook Digg It! Stumble Delicious Technorati

To get future posts delivered directly to your email inbox or to your RSS reader, be sure to subscribe to Obesity Panacea.
You can leave a response, or trackback from your own site.

2 Response to "'Spring Ahead' to a Heart Attack"

  1. Yoni Freedhoff Said,

    Why is Jack Layton having a heart attack?

    Posted on March 17, 2009 at 2:02 PM

  2. Travis Saunders, MSc Said,

    Because he can't believe the Federal Science Minister won't confirm if he believes in evolution. ZING!

    Posted on March 18, 2009 at 10:54 AM


Blog Archive

Recent Posts

Peter's Travel Adventures on PhD Nomads

About Us

We are PhD students in the School of Kinesiology and Health Studies at Queen's University in Kingston, Ontario. Our research focuses on the relationships between obesity, physical activity, and health risk. This blog is our attempt to consider the many "cures" for obesity that we read about on a daily basis. Enjoy.


The opinions expressed here belong only to Peter and Travis and do not reflect the views of any organization. Any medical discussion on this page is intended to be of a general nature only. This page is not designed to give specific medical advice. If you have a medical problem you should consult your own physician for advice specific to your own situation.

Donate To Obesity Panacea