The heart of daylight savings

David Letterman said that daylight savings time is like Robert Downey Jr. getting out of bed; you spring forward and then you fall back. In Australia, where instead of “fall” we use the archaically correct term “autumn” this aphorism is less pithy, but we all know that daylight savings is about turning the clocks forward for spring and summer and then turning them back in autumn and winter. In Australia many states have just turned their clocks back and according to a new study this is good news for those southern hemisphere dwellers but it may not be such good news for their northern hemisphere counterparts as they turn their clocks forward.

The idea of daylight savings is first credited to Benjamin Franklin back in the 1780s but it was not until the first part of the 20th century that it was actually tried. It was the Germans who first introduced daylight savings with the aim of saving on energy and fuel usage. This was based on the idea that changing the clocks reduces the use of artificial lighting in the evening but increases use in the morning, with the assumption being that the evening reduction outweighs the morning increase.

Since daylight savings has spread around the world there has been much debate as to its efficacy. If there is any energy saving in the modern world, given current patterns of usage, the saving is negligible. It has also been said that daylight savings should reduce traffic accidents but again, there is no evidence that it does do this. There is equally no evidence that daylight savings does in fact fade the curtains or the carpets. So amid all of this lack of evidence what do we know about daylight savings? Well, according to a new study, daylight savings might have real impacts on health.

For the study the researchers gathered data from every hospital in Michigan from January 2010 to September 2013. There was a total of 42,060 admissions for heart attacks during the study. The researchers first allowed statistically for the known increase in heart attack rates during the winter and the decrease in rates during the summer. The researchers noted too that heart attack rates are greater on Mondays and lower on weekends. Allowing for all that the researchers wanted to see whether daylight savings had any impact on heart attack rates.

The results showed that the Monday after turning clocks forward saw a 25 per cent increase in heart attack rates compared to other Mondays of the year (which themselves were 34 per cent above other days). The innate rise in Monday heart attack rates is put down to the stress of starting a work week and changes in the sleep wake cycle. The additional boost following daylight savings turning clocks forward is probably due to further disruption to circadian rhythms and loss of sleep. It should be noted though, that the overall heart attack rate the entire week following daylight savings introduction was not greater than other weeks. This suggests that susceptible people simply had their heart attacks accelerated by a few days due to the impact of daylight savings.

On the other hand, the good news is that when the clocks get turned back for autumn there is a 21 per cent drop in heart attacks on the Tuesday following the event. So southerners can rest easy (for six months) and you northern hemisphere types should make sure you get enough sleep and reset that body clock.