Apparently that beloved fairytale had it backwards. According to a new study, there is a reason why women wake before men, and tire more easily in the evenings. Here I thought it was just so they could fetch coffee and breakfast in the morning...
A blog post a wrote a few years ago (http://suupedupscience.blogspot.com/2011/07/less-rhythm-less-sleep.html) talked about circadian rhythm (the body clock) and how neural rhythms determine so many body functions. A new study shows that men and women are biologically designed to go to bed at different times. Female circadian rhythm runs faster, and therefore they tire earlier and wake up earlier than men. Male rhythm predisposes them to sleep and wake later, and are therefore more likely to be night owls.
The study was led by Jeanne F Duffy, associate professor of medicine at Harvard Medical School, and is the first to find a difference in the body clocks of different sexes. She said 'We found that women are twice as likely to have a circadian rhythm shorter than the normal 24 hrs and mre likely to get sleepy in the evening.'
By contrast, men are more likely to have a rhythm that is longer than 24 hours.
The study involved 200 people and took a month. The subjects were not told the time and were kept in subdued light. The production of melatonin (a hormone that is involved in circadian rhythm) was measured and showed that the average male internal cycle lasts 24 hours and 11 minutes, 6 minutes longer than for woman.
This may not seem like a big difference, but becaus circadian rhythm affects your sensitivity to multiple external factors (like light), it can effectively mean a matter of hours. Duffy explains, 'Morning light exposure aligns us to the 24-hour clock, so if you in on Sunday, it's harder to wake up on Monday.' So if women expose themselves to light in the evenings, they can slow down their cycle, whereas men can do the opposite.
Now I know there is a reason why my mother always insisted on my going to bed at the same time every night. I wonder if there is a reason female cycles are faster. I think back to our hunter-gather days, men would so often be working harder chasing things to kill, so perhaps those who got too tired died out, and so the ones that could stay up later survived, whereas with women, it didn't matter because they were just looking after the cave hearth...
Credits: The Sunday Times 28.08.11,