Response to Daylight Saving Time Impacted by Genomic Heterogeneity

A study published today in Scientific Reports shows that DNA plays a role in how much the "spring forward" time change affects individuals. People whose genetic profile makes them more likely to be "early birds" the rest of the year can adjust to the time change in a few days, but those who tend to be "night owls" could take more than a week to get back on track with sleep schedule.

The study uses data from continuous sleep tracking of 831 doctors in the first year of post-medical school training. From the large UK Biobank dataset, the researchers calculated genomic "chronotype" predisposition information, also known as the Objective Sleep Midpoint polygenic score. People with low scores were genomically predisposed to be "early birds" and those with high scores were genomically "night owls."

The team then applied these genomic scores in the intern sample and focused on the two groups of about 130 physicians each that had the strongest tendencies to be "early birds" and "night owls" based on their scores. The researchers looked at how their sleep patterns changed from the week before DST to the weekend after it.

In general, the difference in post-DST weekday wakeup times between the two groups was not large—probably because first-year medical residents have very strict work schedules. In fact, the stressful duties and demanding schedules that interns endure is what made this population such an interesting one to study, and the larger Intern Health Study that the data come from has yielded important findings about the relationship between stress, sleep, genetics, mood and mental health.

But the time they got to sleep on the nights before workdays, and both sleep and wake times on the weekend, varied significantly between the two groups. The DST change made the differences even more pronounced. Early birds had adjusted their sleep times by Tuesday, but night owls were still off track on the following Saturday.

The paper’s senior author Margit Burmeister, from the University of Michigan, says the study gives one more strong reason for abolishing Daylight Saving Time. "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," she says. "These 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."