Question: Hi there, I was in the recent live chat and thanks for answering my questions. I would like to ask has sleeping patterns changed significantly in the past centuries?

Rachel Sharman answered on 15 Nov 2018:

Hi, I remember the chat! Another amazing question. Yes it has!

At dusk, our sleep hormone (melatonin) rises. It peaks in the middle of the night and then decreases. It makes a n shape curve. Although melatonin doesnt really make us sleepy, it is released by the master clock in the brain and tells all the clocks in the cells in the body that it is night. So we sleep better when melatonin is high.
From historical diaries we see loads of reports of first and second sleep. Without electronic light, we think people would go to sleep at dusk. Rise in the middle of the night, have a meal and speak to friends (there are even religious prayers found for this time of the night!) then go back for their second sleep. So this would make their melatonin a m shaped pattern. This is called bimodial and we do see some people who have a slight dip at the peak of their melatonin curve. Like an evolution fingerprint!
For my research, we know that sleep durations are getting shorter too. Studies have shown the teenagers sleep has been getting shorter over the last centuary. Researchers are now trying to work out why. Is it that our lifestyles are now more sedentary (office work) or is it through electronic lights (we are no longer at the mercy of the sun!). To answer this, researchers are evaluating the sleep of people in remote towns around the world where they dont have electric or are just getting electric to see if their sleep changes. Im always jealous of those researchers and the amazing places they get to visit but then again, I dont think I could live without electric!!