We evolved on a rotating planet, with regular patterns of light and dark exposure, and our biology is set up to work with this cycle. Our kidneys produce less urine, our body temperature is lower and our immune systems are less capable of fighting off foreign invaders at night. During the day, blood pressure rises, hunger hormones kick in and our brains shift into a higher gear. These daily fluctuations in our biology are called circadian rhythms, and they dictate when we feel sleepy.
For most of human history, we slept at night and were more active during the day.
These same studies have found that, on average, people from traditional societies go to bed and wake up several hours earlier than we do in developed countries. Not only do they sleep earlier than us, they also seem to sleep better. Between 10 and 30% of people in developed countries experience chronic insomnia, whereas just 1.5% of Hadza people (Tanzania), and 2.5% of San people (Namibia) say they regularly have problems falling or staying asleep. Neither group has a word for “insomnia” in their language. Continue here....
-- Linda Geddes
