If you live in a country where daylight saving time (DST) is observed, you'll be familiar with the biannual shift that our body clocks have to undergo. For some, coping with the change is harder – and a new study suggests that the number of days it takes to adapt could be down to our genetics.
In a study of around 830 people, researchers found early birds who usually went to bed earlier weren't as badly affected by DST as night owls who tended to stay up late.
The findings could have important implications for how we understand the workings of our circadian rhythm – the natural process that tells us when it's time to go to sleep and when we should be getting back up again, and which is important for our health.
"This study is a demonstration of how much we vary in our response to even relatively minor challenges to our daily routines, like DST," says neuroscientist Srijan Sen, from the University of Michigan.
"Discovering the mechanisms underlying this variation can help us understand our individual strengths and vulnerabilities better."
From a sample of 831 interns at medical school, the researchers used genetic DNA profiling and a measure called the Objective Sleep Midpoint polygenic score to sift out the main study candidates: the 133 individuals most genetically predisposed to be early birds, and the 134 individuals most genetically predisposed to be night owls.
The team then used wearables to track the response of these interns during the DST change in spring in the US (when the clocks go forward an hour). While all the volunteers continued to get up at similar times on weekdays, there were significant discrepancies in the times they went to bed, and in the going to bed and getting up times on weekends.
Overall, the early birds had more or less adjusted to the new timings by Tuesday after the DST shift on Sunday morning. However, as a group, the night owls were still struggling to come to terms with the change in time by the following Saturday.
For the researchers, it's yet more evidence that DST does more harm than good.
"It's already known that DST has effects on rates of heart attacks, motor vehicle accidents, and other incidents, but what we know about these impacts mostly comes from looking for associations in large data pools after the fact," says neuroscientist and geneticist Margit Burmeister, from the University of Michigan.
"This data from direct monitoring and genetic testing allows us to directly see the effect, and to see the differences between people with different circadian rhythm tendencies that are influenced by both genes and environment. To put it plainly, DST makes everything worse for no good reason."
The research team also looked at the DST shift back an hour, which happens in fall in the US. Here there were no significant differences in how early birds and night owls adjusted, suggesting our bodies find it easier to cope with that particular change.
While the idea of DST is to give us more hours of daylight in the summer months – hence the name – its continued observance continues to be controversial. Some experts say that the damage done to our natural circadian rhythms and the knock-on effects on our physical and mental health outweigh any potential benefits of the practice.
However, the research has implications far beyond DST – which the team used as a convenient way of measuring how our bodies adapt to new rules about when to go to bed and when to get back up again. Future studies could look at the link between genetics and more substantial changes in body clock patterns.
"These genetic differences may affect how individuals adjust to jet lag or shift work as well," conclude the researchers in their published paper.
The research has been published in Scientific Reports.