Is it True that People Born in Summer Need Less Sleep than People Born in Winter?

Why do some people seem to need less sleep than others? Why is it so easy for some people to get up in the morning and for others it's easier to stay up late at night?

As far as we know, there is no data on the association between sleep patterns and birth dates. I even asked an expert on the topic: Prof. Dr. Till Rönneberg from LMU Munich. However, he told me that this has not been investigated in depth. What has been thoroughly investigated though is why some people are early birds and some are night owls. This has to do with our inner clock that has evolved to help us anticipate the daily changes in our environment, such as light-dark cycles or temperature cycles. Almost everyone’s inner clock is happily ticking away with an approximately 24-hour period (that is why it is termed “circadian clock”- circa dias - almost a day). However, the ticking speed varies. Imagine you have a fast inner clock. This means that you would be too early for everything: you wake up early, eat early and get tired early; you would be an early bird, or as the scientific community terms it - an early chronotype. The opposite is also true; late chronotypes have a slow inner clock, so they are “late” for everything.
The interesting thing is that our chronotype varies throughout our life; we all start off as very early chronotypes, our clocks become gradually slower until puberty and then getting earlier again during the rest of our lives. Not only is our chronotype age-dependent, but also sex-dependent.
These differences in individual chronotypes are definitely something which we have to keep in mind when discussing school hours or office hours. These are often much too early especially for school children in the midst of puberty.
Last but not least, I want to mention an important feature of our inner clock, and that is that it is able to synchronize to our environment through light. This means that it can entrain the 24-hour day-night cycle provided it receives enough light input. To cut it short, the more light we get, the easier it is for night owls to get up in the morning and the longer early birds can stay up at night.

Reference

Rönneberg and Merrow, Cold Spring Harb Symp Quant Biol, 2007

by Veronika Lang
this article originally appeared 2013 in CNS Volume 6, Issue 4, Integrative Medicine

Do you also sometimes wonder about the simple neuroscientific questions in everyday life, but don’t really feel like looking them up right away? For questions like this, just mail us your question (cns-newsletter@charite.de) and Dr. Harebrained will give us his explanation in the next issue!