Is your wife too tired for sex? Blame her faster circadian rhythms

Women may be too tired for sex in the evenings because their circadian rhythms are faster than men's and so they need to go to sleep earlier, according to a new study.

Women's circadian rhythms run six minutes faster than men's, making them much more likely to be early birds rather than night owls.

Harvard researchers have found that women report early morning insomnia around 50% more frequently than males. Once they wake up, they have difficulty going back to sleep.

It helps to explain why women are often up with the lark, while their partners stay slumbering long into the morning.

However, women may end up being chronically sleep-deprived because they try to fight against their faster sleep cycles and fit too much into the evenings, before being woken up too early by the morning light.

“What we found was that the cycle length of the biological clock in women was shorter on average than it was in men,” the Daily Mail quoted Jeanne Duffy, one of the study's authors as telling NPR.

“The average difference was about six minutes,” she added.

According to Charles Czeisler, professor of sleep medicine and physician at Harvard Medical School, millions of women are fighting against their faster circadian rhythms every day.

The Harvard-affiliated Brigham and Women’s Hospital have released the study findings.