Many of us have never been quite clear why daylight saving time (DST) exists, and have only been aware of the very abrupt schedule change. Like moving from one time zone to another, it seems to take days or even a week to fully adjust to changing everything by one hour. Those of us with pets or small children are also aware that without the ability to read a clock, DST has no effect and often makes life more complicated. Proponents say that changing the time reduces energy usage and helps children to get outdoor exercise.
As scientists continue to learn more about the staggering benefits of good sleep and the drastic problems associated with bad sleep, they are finding that the sleep disruption associated with shifting the day by an hour has the potential to cause problems that should not be ignored. So let’s take a look at the current state of DST, what its purpose was originally and if it has been hitting those goals or causing more problems than it is worth.
What is the point of daylight saving time?
The idea behind daylight saving is to change the schedule so there is more time before bed during the summer months when there is more daylight. So In mid-March all clocks are set forward. Then, when daylight starts to decline again, everything goes back. The US is in DST two-thirds of the year, for 34 weeks.
This chart shows the average daylight hours for each month, when DST occurs, and when the waking hours overlap assuming a 6am wakeup time. Some sunlight is given up in the morning so evening sunlight is easier to get.
Many countries have some form of time-shifting daylight saving. In the US the Uniform Time Act of 1966 means that states may opt out of daylight saving time, but may not be permanently on daylight saving time.
The reactions over the years have been very mixed, and the benefits have not been clear. Everyone seems to dread the loss of an hour in the middle of the night and celebrate the gain of an hour later in the year. Because pretty much everyone transitions with daylight savings, there has been ample opportunity to study DST and what kind of impact the transition has.
Good Sleep is Better than More Sunlight
While the appeal of having set hours to enjoy the sun in the summer sounds like it would make for the perfect rest after, the abrupt transition of a full hour causes a lot of problems. The American Academy of Sleep Medicine followed the international Society for Research on Biological Rhythms and published a letter in a leading medical journal declaring that the transition “incurs significant public health and safety risks, including increased risk of adverse cardiovascular events, mood disorders, and motor vehicle crashes.”
One large study found that after the change, most people lost about 30 minutes of sleep per night for four nights. They also found reports of poor sleep rose by eight times from 1.7% to 13.6% and reports of being totally unrested rose by five times from 1.7% to 8.5%. A different study found 60 minutes of lost sleep on average for the 10 days after the Spring transition, and a 10% drop in sleep efficiency.
Moving the time impacts our circadian rhythm regardless of our personal sleep patterns. “Morning” people who find it easier to get out of bed after sleep tend to have difficulty falling asleep after the fall transition. For “evening” people who find it easier to stay up late, the loss of an hour in the Spring made for more restlessness and difficulty getting to sleep.
Sleep experts say that a gradual transition can help to mitigate a lot of the problems. The American Academy of Sleep Medicine suggests shifting your wake and sleep times by 15 minutes a day, starting three days before the transition. There are very few apps or products that can help with this gradual transition, so most of us have to do it ourselves.
Losing Sleep Isn’t Just About Being Tired
None of us prefer to lose sleep and feel tired, but the study of DST has been able to tease out the more drastic impacts of abrupt sleep wake cycle changes. Having a bad night of sleep after a DST transition can just make life feel more difficult, particularly if young children are part of the equation.
One study that looked just at the fall transition, which gives everyone an extra hour of sleep, found that admissions of heart attacks patients to emergency rooms drops for about 4 days after. The authors attribute this finding to widespread sleep deprivation that is ultimately causing heart attacks. Forcing an extra hour of sleep prevents some of the heart attacks that would have happened the following day otherwise.
A massive study on tens of millions of Americans picked up on four distinct unhealthy diagnosis clusters after the DST transition at both times of the year- heart disease, injury, mental health problems, and infections related to an impaired immune system. The transition affects different groups of people in different ways. Men, for example, were found to be more susceptible to substance abuse after the transition, which can compound the already existing sleep problem. The researchers settled on the following numbers for the whole US population, though they were only able to count people with medical insurance. The two shifts when DST begins and ends adds somewhere in the ballpark of the following degree of misery:
- 6,000 more diagnoses of heart disease
- 3,000 more people over 60 admitted for ischemic heart disease (heart attack or imminent heart attack)
- 5,000 more incidents of behavioral and mood problems in 11 to 20 years olds
- 2,000 more diagnoses of inflammatory autoimmune gut diseases like colitis
Most of the diseases occurred in the older (over 60) or the younger (under 20) populations. Also the under 20 group was more likely to injure their head, wrist, or hand, while the over 60 folks were more likely to sustain injuries to the torso.
There is a very long tail of associated issues with DST. The social fabric of our society relies on well-rested people and in the days after the transition people are less friendly and give less to charities. Fatal car accidents are higher, and an Austrian study found a 3% rise in death from all causes in the week following the Spring transition. A Danish team looked at depression and found that for 10 weeks after the fall transition episodes of depression increase by about 11%.
It’s not just you, there is ample empirical evidence that the practice of changing our clocks by an hour twice a year is not healthy.
How We Stop this Menace
First, we need to figure out if there is a difference in the two schedules. When midnight happens according to the clock has an influence on our circadian rhythm.
It is very clear that the transition is unhealthy, and the evidence isn’t complete on which schedule is better permanently but leans toward regular time. One study found that permanent DST could reduce pedestrian fatalities on the road by 13% and driver fatalities by 3%, but this study appears to be the exception in the literature.
Sleeping in later and keeping summer time all year round is appealing, but a case study found that regular time is best for our circadian rhythms. There was a noticeable difference in the consistency of the circadian rhythms with people who went by regular time year-round, with greater benefits for areas with larger seasonal changes. Both international and US experts agree that permanent regular time would be most healthy.
So far only the US state of Arizona has taken up congress’ offer to ignore DST. The rest of the states have a patchwork of attempts to at least stop the time change, with most passing laws that attempt to force congress to institute permanent DST despite the experts’ recommendations.
When daylight savings time adds an extra 2am early on March 12th this year, many of us will not notice as it happens automatically. But we should consider undoing that automatic shift and setting the same wakeup relative to the sun each day.