There’s an important variable that influences your internal clock: sex. It turns out, male and female circadian rhythms don’t exactly match up. Men’s clocks tend to run truer to a full 24-hour cycle or longer (on average, men have a circadian cycle that’s six minutes longer than for women ) meaning they may feel less tired in the evening. In women, the internal clock is more likely to be shorter than a full 24-hour cycle, making it more likely that they will awaken earlier, which may also increase their susceptibility to early-waking sleep disturbances like insomnia.
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