"Circadian timing is set to an earlier hour in women than in men, so they may fall asleep earlier," explains Dr. Nayantara Santhi. "Women also tend to wake up earlier than men and exhibit a greater preference for morning activities than men."
"Overall, this means that women have a later biological time of sleep (i.e., an earlier circadian phase relative to the timing of sleep). This delayed biological time of sleep may be a contributing factor to the higher incidence of insomnia in women."
Some women may also struggle to sleep if they're feeling stressed at bedtime. A relaxing routine and calming tea or a cup of warm milk may make it easier to deal with stressful thoughts before a woman gets into bed.