Chronotypes: morning and evening people are a matter of the clock, not of willpower

“I am not a morning person” is usually treated as a matter of willpower or habit. Chronotype research says something else: it is a question of where the body’s clock is set.

1. Not types, a continuous distribution

First, a common misreading. Morning and evening are not two categories. They are the ends of a distribution across the population, and most people sit near the middle. The ends simply have names.

Two instruments dominate.

Instrument	What it asks	Year
MEQ (Morningness-Eveningness Questionnaire)	When you prefer to be active	1976
MCTQ (Munich ChronoType Questionnaire)	When you actually sleep and wake on free days	2003

The difference matters. MEQ asks about preference; MCTQ measures the mid-point of sleep on days without an alarm. The latter comes closer to the phase of the body clock itself.

2. It moves with age

A chronotype is not a fixed trait of character. It shifts systematically across a life.

• Children are relatively early.
• Through adolescence it grows later, reaching its latest around the late teens or about twenty.
• After that it moves earlier again with age.

This unsettles the view of teenagers sleeping late as laziness. The delayed phase at that age is a biologically expected change. Reports of improved sleep duration and daytime alertness at schools that pushed start times later fit the same observation.

3. Social jetlag

The most practical concept in the field. It measures the gap between the mid-point of sleep on working days and on free days.

If you are dragged earlier by an alarm through the week and catch up at the weekend, the body carries something like the load of shifting time zones every week. Repeating that adjustment is why it is called social jetlag.

Things have been observed in people with large values — but they are correlations, not demonstrated causes. Evening types with large social jetlag show less favourable figures for smoking, drinking and some metabolic markers, but whether that follows from the chronotype or from a misaligned schedule has to be kept apart.

4. Can it be changed?

Partly.

• Light is the strongest signal. Morning daylight pulls the clock earlier; bright light at night, screens included, pushes it later.
• Fixing the wake time works better than fixing bedtime, because the moment you fall asleep is not directly under your control.
• But moving an inborn phase very far is hard. Adjusting the schedule while remaining an evening type is more realistic than converting into a morning one.

5. What to do with a result

• A chronotype is not good or bad. Society is simply arranged around the early end.
• Knowing your phase lets you decide where to put what matters. The hours of high alertness differ from person to person.
• If social jetlag is large, look first at moving weekday bedtime a little earlier rather than catching up at weekends.
• If you cannot fall asleep, or are unbearably sleepy in the day, look at sleep disorders before chronotype.

References

James A. Horne & Olov Östberg (1976) A self-assessment questionnaire to determine morningness-eveningness in human circadian rhythms, International Journal of Chronobiology 4(2) — the source of the MEQ.

Till Roenneberg, Anna Wirz-Justice & Martha Merrow (2003) Life between clocks: Daily temporal patterns of human chronotypes, Journal of Biological Rhythms 18(1) — the MCTQ and the mid-sleep measure.

Marc Wittmann et al. (2006) Social jetlag: Misalignment of biological and social time, Chronobiology International 23(1-2) — the origin of the concept.

Till Roenneberg et al. (2004) A marker for the end of adolescence, Current Biology 14(24) — chronotype reaching its latest in the late teens and turning back.