Notes on "SLEEP A Very Short Introduction"
I recently finished “SLEEP A very short introduction” by Steven W. Lockley and Russel G. Foster. It is part of the A very short introduction series by Oxford University Press which tries to compress broad fields into short books for readers to get a general understanding of the matter. Because SLEEP is arranged thematically, I will not write a normal review, but iterate through the points I found most interesting.
Circadian rhythm and sleep pressure
One of the first things I learned is that tiredness is regulated by two independent mechanisms: Circadian rhythm and sleep pressure. The brain naturally generates a 24-hour rhythm, structuring the day and making it easier to fall asleep at night. Additionally, a form of pressure builds up during wake time and dissipates during sleep. The substance responsible for this has not been positively identified and it seems likely that several mechanisms are at work.
Early birds and night owls
Some people really are more productive in the morning, while others prefer the evening for work. These differences are real and genetically determined. I always thought that this would be more of a personal preference.
Christmas dinner
There is some evidence that people in the past slept longer and that sleep duration depended on the season. The authors suggest that electric lamps could be responsible for the increase in BMI in the last 150 years. For thousands of years, humans build up fat reserves in the summer and used them up in the winter. The loss of seasonality produced by the constant availability of lighting could have upset this balance.
Don’t wake me, I plan on sleeping in
An interesting fact I learned is that sleep duration after receiving a vaccination has an effect on the level of antibody protection developed. The book refers to an experiment where two groups were inoculated with an influenza vaccine and allowed to sleep 4 and 7.5-8.5 hours respectively. The sleep deprived group’s antibody level was less than half of the control group’s afterwards. I was not able to find the exact study referenced, but a similar one [1] which concludes “Analyses focused on nightly sleep on the days preceding and after the vaccination revealed that shorter sleep duration on the two nights before the vaccination predicted fewer antibodies 1 and 4 months later”.
Slurp, slurp
On caffeine, the book reports
The drug has a long ‘half-life’ – about 5 hours, and longer under some circumstances – meaning that it takes about 5 hours to metabolize half of the circulating amount. This means that if someone has a coffee or soda containing 100 milligrams of caffeine at 10 a.m. in the morning, there are still 25 milligrams in the body by 8 p.m. at night, and about 12.5 milligrams at bedtime, which causes measurable disruption of sleep.
That pairs well with my recent article on caffeine and another reason to treat the stuff with suspicion.
Sleep and idea generation
The authors present an impressive list of scientific and artistic contributions achieved during or directly after sleep, ranging from the periodic table to The Strange case of Dr Jekyell and Mr Hyde. The book doesn’t offer a lot of details, but I would be interested in learning how to weaponize this.
References