Whether you're a morning person or a night owl was decided partly before you were even born

[Glenn83]

Chronotype, the term for your body's natural preference for sleeping, waking and feeling alert at particular times, is governed by circadian clock genes including PER2, PER3 and CRY1. A landmark 2019 genetic study of nearly 700,000 people identified more than 350 gene variants associated with chronotype, most enriched in brain regions controlling the retina, hypothalamus and pituitary gland, the parts of the body responsible for sensing light and regulating the body's master clock.

That said, no single gene fully determines whether someone is a lark or an owl. Chronobiologist Till Roenneberg of Ludwig Maximilian University in Munich points out that at one point in human history, morning larks and night owls probably differed by only a few hours, a gap that has widened considerably as modern life pulls people further from natural light cycles and deeper into screens at night. A 2012 analysis of nine years of sleep survey data found the average chronotype had shifted about 15 minutes later over that period, a small but statistically real drift toward eveningness.

The genetic research also found that being a morning person is causally associated with somewhat better mental health outcomes, though it showed no meaningful effect on body mass index or type 2 diabetes risk.

Sleep researchers increasingly argue the real health concern isn't which chronotype you happen to have, but whether you're actually living in sync with it. Being forced to keep a schedule that fights your natural circadian rhythm, a phenomenon researchers call social jetlag, is linked to worse sleep quality and increased metabolic risk regardless of whether you're naturally a lark or an owl to begin with.

Night Owl Chronotypes in a Morning Lark Worldwww.brainfacts.org