Larks and owls: are you a morning or evening person?

What is a chronotype?

It is the timing your body clock prefers: when you naturally feel sleepy and when you naturally wake if left to yourself. Researchers usually measure it with questionnaires, such as the Munich ChronoType Questionnaire, which more than 55,000 people had filled in by 2007. They found that chronotype is spread along a smooth range, like height. A minority are strong larks or strong owls; most people are somewhere in between.

A practical way to estimate yours is the midpoint of your sleep on free days, when you don’t set an alarm. If you’d sleep from midnight to 8am, your midpoint is 4am.

What makes someone an owl?

• Genes. Chronotype runs in families, and dozens of gene variants linked to it have been found.
• Age. Children are usually early risers. During puberty the clock shifts later, reaching its latest around the age of 20, then moves gradually earlier for the rest of life. That’s why many teenagers can’t fall asleep early and many older people wake at dawn.
• Light. People who see little daylight and lots of evening light drift later. City dwellers tend to be later than people who work outdoors.

Is being an evening person bad for you?

In UK Biobank, which followed 433,268 adults aged 38 to 73 for an average of six and a half years, people who called themselves “definitely an evening person” had a 10% higher risk of dying during the study than definite morning people, after adjusting for age, sex and other factors. Evening types also had more diabetes, mental health problems and lung and digestive problems.

That doesn’t prove the chronotype itself causes harm. Evening types in the study were more likely to smoke, drink and sleep less, and much of the problem may come from living out of step with their clock: getting up for work long before their body is ready, then catching up at weekends. Researchers call this gap “social jet lag”.

What can owls do?

• Use light. Get outside in daylight soon after waking, and keep the last couple of hours before bed dim. This is the strongest way to pull your clock earlier.
• Keep the wake time fixed, even at weekends. A long lie-in on Sunday pushes the clock later and makes Monday harder.
• Avoid late caffeine. Owls are more likely to lean on coffee in the afternoon, which delays sleep further. See caffeine and sleep.
• Work with your type where you can, for example by doing demanding tasks later in the day if your job allows.

If your sleep timing is so late that you can’t get up for work or school even with these steps, and you sleep well when allowed to sleep late, you may have delayed sleep phase syndrome, which a GP can refer you for. See when to see a GP.