Why is it that a man feels at his sexiest when he wakes up in the morning but a woman wants to go back to sleep? And why, late at night, when a woman is in the mood for love, is her man just lying there, snoring? It all comes down to hormones. Here's why our sex clocks don't always tick in time.
5 AM
Even before a man wakes up, his testosterone levels are at their peak -between 25-50 per cent more than at any other time of the day. That's because the pituitary gland -which governs the production of the male sex hormone -has been switched on in the night and levels have been steadily rising until dawn.
Women also make testosterone -the main sex drive hormone -but produce a fraction of the amount and it rises by only a tiny bit overnight. It is also kept in balance by oestrogen and progesterone. Men need only a normal amount of testosterone to feel like having sex. The raised levels in the morning means most men will wake up two to three times a week with erections.
6 AM
Slept well? A good kip is another reason a man may feel even more amorous in the morning. Studies have found that the longer and deeper a man has slept, the higher his testosterone levels. Research in the Journal of the American Medical Association shows getting more than five hours' sleep can raise male levels by an extra 15 per cent.
7 AM
While a man's levels of sex hormones are at their highest when he wakes up, a woman's are at their lowest. Male and female testosterone levels are at their highest at opposite ends of the day, so they are out of sync, says consultant gynaecologist Gabrielle Downey, of the Sandwell and West Birmingham Hospitals NHS Trust.
Downey says it takes more than hormones to get a woman in the mood, so men need to make an active effort."
Women's hormones rise and fall more over their monthly cycle than through the course of a day. At their height -midway through her cycle -a woman's levels of testosterone will be 30 times higher than at the start.
8 AM
As both sexes get ready for the day, levels of the stress hormone cortisol rise to help them wake up -and dampen the effect of sex hormones. Cortisol, studies show, lowers the sex drive of both men and women.
As the day goes on, men steadily make testosterone. The hormone is needed to trigger muscle growth and sperm production. Levels will fall and rise every 90 minutes through the day as part of the body's in-built clock.
