Why do some people wake up easily and others don't?
Three factors dominate: chronotype (genetic morning vs. evening preference), sleep quality (deep vs. fragmented), and sleep duration. Genetics account for about 50% of chronotype variance.
Chronotype genetics
Studies on twin pairs estimate that 40–50% of chronotype variance is heritable. PER and CLOCK gene variants are well-documented contributors.
Sleep quality matters
Even a 'morning person' will struggle to wake easily after a fragmented or short night. Conversely, deep, well-timed sleep can make a late chronotype temporarily morning-friendly.
You can shift, but not eliminate
Light therapy and consistent schedule shift chronotype by up to 1–2 hours over weeks, but you cannot turn a true night owl into a 5 AM riser permanently.
Sources
- Matthew Walker, Why We Sleep (Scribner, 2017). Why We Sleep: Unlocking the Power of Sleep and Dreams
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