The Clocks Go Back. Your Body Clock Doesn’t: The Genes Behind Morning People and Night Owls

This month, most of Europe and North America will move the clock on the wall back by an hour: on Sunday 25 October in Europe, on Sunday 1 November in the United States. The clock inside your body will not move with it. It keeps its own time, and for a few days the two disagree.

Some people barely notice. Others feel off for a week. Part of that difference comes from how your body clock is set to begin with, and part of that is written in your DNA.

351 places that set the clock

The body clock, or circadian rhythm, is the roughly 24-hour cycle that tells you when to feel sleepy and when to feel awake. Whether you are a morning person or a night owl is the everyday sign of where yours is set.

Jones et al. 2019 asked 697,828 people from UK Biobank and 23andMe whether they were morning people, and searched their genomes for the answer. The number of places in the genome known to be linked to being a morning person went from 24 to 351. Several sit in the classic clock genes, such as PER3, where this site has rs228726; others are in genes like AK5 (rs12030598) and FBXL13 (rs76187115).

Real, but small: 25 minutes

Saying you are a morning person is one thing; going to sleep earlier is another. So the researchers checked: 85,760 people had worn activity monitors that recorded when they actually slept. The 5% carrying the most "morning" variants fell asleep on average 25 minutes earlier than the 5% carrying the fewest.

That is the honest size of it. The genes are real, they add up across hundreds of places, and even between the two extremes the difference is less than half an hour. The rest is light, habit, work and everything else in a life.

Why the clock genes are in your eyes

The study found these genes active in the retina, the back of the eye, as well as in parts of the brain that keep time and control hormones. That fits what is known about the clock: light reaching the eye is the main signal it uses to stay in step with the day. An hour's shift on the wall clock is, to the body, an hour's shift in when the light arrives.

Morning people and mood

The study also used the genetic variants to test cause and effect. Being a morning person was linked to better mental health, while it did not change body weight or the risk of type 2 diabetes. That is a finding about large groups of people, not a reason to change your own habits, and the sleep topic follows the same question across other studies.

Where this touches this site

The sleep and circadian rhythm page gathers the positions from this and other sleep studies, and an earlier post looked at how the same clock reaches your blood sugar. The Gene Knowledge Graph shows each clock gene with everything it connects to.

So if the new hour feels strange for longer than it does for the people around you, part of the reason may be a clock that was set a little differently from theirs. The clock on the wall changed this month. The one inside was set long before.