Is your wife 'too tired' for sex?

They run on a different biological sleep clock to men and need to go to bed earlier because of it," says a new Harvard 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.
Jeanne Duffy, study co-author from Harvard, said, "What we found was that the cycle length of the biological clock in women was shorter on average than it was in men. The average difference was about six minutes."