24% of Under-30s Are Morning People. 63% of Over-60s Are. Nobody's Genome Changed
A study of 89,283 people found 15 genetic regions associated with being a morning person, seven of them near known circadian clock genes. It also found that age shifts chronotype far more than any variant does.
Among people under thirty, 24.2% describe themselves as morning people. Among people over sixty, 63.1% do.
That is the same species, largely the same gene pool, and a completely different answer. Whatever makes someone a lark, it is not fixed at conception.
Chronotype shifts across a lifetime. The genome does not.
The study
Researchers analysed self-reported morningness in 89,283 individuals of European ancestry, testing around 8 million genotyped or imputed markers. They identified 15 genome-wide significant loci, seven of them close to well-established circadian genes including PER2 (Hu et al., Nature Communications, 2016).
Pathway analysis pointed at two systems: circadian regulation, and phototransduction — the machinery by which the retina converts light into the signal that sets the clock in the hypothalamus.
That second one is the more interesting finding. Part of what separates a lark from an owl may be how a person's eyes report the arrival of morning.
What morningness travels with
In the same cohort, morning people were:
| Morning people | Night people | |
|---|---|---|
| Insomnia | 12.9% | 18.3% |
| Odds of needing >8h sleep | OR 0.67 | — |
| Odds of depression | OR 0.64 | — |
Morningness was also more common in women (48.4%) than men (39.7%).
Here is where the paper does something many popular write-ups skip. The authors tested whether these associations were causal using Mendelian randomisation — and found no evidence that they were. Morningness travels alongside lower depression and lower BMI in this data. It does not follow that becoming a morning person would change either.
Age beats genotype
Return to the opening numbers. Chronotype moves enormously across a lifetime — from roughly a quarter of under-thirties to nearly two-thirds of over-sixties preferring mornings.
No genetic variant in this study comes close to that effect size. Each of the 15 loci nudges the odds. Age, light exposure, shift work, having a newborn, and the simple fact of getting older move the needle far more.
Anyone selling you a genetic explanation for why you cannot get up should be asked how it accounts for the fact that you probably will, eventually, without any change to your DNA.
What the app reports
Sleep Zzzz applies the variants identified by Hu and colleagues to your genotype and shows where you fall on the morningness distribution from that study.
Read it as a mild tendency, measured in a large but ancestrally narrow sample, against a trait that visibly changes with age. It is a genuine signal. It is not an excuse, and it is not a schedule.