Most (but not all) Americans participate in daylight savings each year, pushing sunrise back by one hour in March and bringing it back on the first Sunday in November. The history of daylight savings is long and complicated- it was used to support the war efforts of both World Wars and to conserve energy during the 1973 oil embargo. The current schedule was set by an act of Congress in 2005 and has been observed that way ever since. Daylight savings has always been controversial, it seems to defy logic and its relevance is under constant scrutiny. The economic impact of a longer evening has also been the subject of much criticism. I will not discuss the logistical and/or economic implications of daylight savings in this post, rather I will seek to apply scientific study to the idea that the current practice might actually be impacting public health and safety.
Risk of heart attack:
Naturally, skipping an entire hour of the night for the sake of implementing daylight savings shortens the amount of sleep that most people on fixed schedules get for that night. In 2011, a team of researchers from the Swedish Register of information and Knowledge about Swedish Heart Intensive Care Admissions (RIKS-HIA) conducted a study using statistical analysis to demonstrate that there is indeed an increase in the number of heart attacks suffered during the first week after the start of daylight savings. They were able to conclude (with a confidence interval of 95%) that there was a 4 percent increase in heart attacks that can be attributed to the beginning of daylight savings. The possible mechanism for the causal relationship might be more complicated than just losing an hour of sleep, according to an article published by Medical Daily. It postulates that the adverse health affects (including heart attacks and strokes) are likely more a result of the sudden change of environment than of one hour less sleep. This idea is supported by a 2007 study involving 50 test subjects that examined the disruptive effects of daylight savings on natural human adjustments to seasonal changes in sunrise. Essentially, the researchers found that the participants transitioned through the changing time of sunrise well without DST but did not when DST was in effect. Considering the evidence that circadian rhythms can affect hear attacks, this mechanism is certainly plausible and the affects could theoretically be avoided with the elimination of daylight savings.
Increase in stress:
There is experimental evidence to support the possibility that the sudden shift of time during daylight savings can cause stress. The 2014 study, which lasted 13 years, examined the differences in cortisol levels in 27,569 people who were subjected to different sunrise times. Cortisol level is a key indicator of stress. They also made sure to exclude anybody taking any kind of confounding medication or having a preexisting condition that might affect or skew beginning cortisol levels. The data showed a 5% increase in cortisol level in the bloodstream for each hour that sunrise was pushed back. The extremely damaging effects of chronic stress are well documented and certainly worthy of prevention. If the abrupt delay of sunrise can act as an additional stressor to humans, it begs the question of whether it is really worthwhile to continue the tradition of daylight savings.
The health affects of daylight savings might not be entirely negative, according to some studies. For example, better road visibility due to a later sunset might prevent some car accidents. This study, conducted in Minnesota, found that even though there are more cars on the road during times when daylight savings is in effect, there is still a noticeable decline in motor vehicle crashes. This supports the idea that DST can actually be helpful and practical in some ways during the later parts of the say. Another study, involving 23,000 children, found that more daylight in the evening leads to a decrease in childhood obesity. The mechanism for this lies with the fact that kids play more when the sun is out than they do when it is not. It is important to note that the changes were rather small, but impactful when extrapolated to an entire population.
Take home message:
Daylight savings originated with a specific purpose that is no longer relevant today, yet it remains an integral part of our yearly schedule. Scientific studies establish causal links between daylight savings and several noteworthy health risks and some benefits. Different people might weigh the pros and cons differently, but I conclude from my research that this is certainly a conversation worth having and worth researching further. Lives could depend on it.
Note: The pictures themselves are links to their sources.