Your biological clock is driven mainly by the light received through your eyes, with bright blue light slowing the production of melatonin and making us feel awake. This therefore provides a logical explanation of why we feel more awake in the summer than in the winter. It is light for longer and the light is stronger.
The ambient temperature also appears to have an effect. We recently compared details in our Auping Better days app with data from the Royal Netherlands Meteorological Institute (KNMI). When we compare the average number of hours slept per day with the average temperature on that particular day, we can see a definite correlation:
This phenomenon also emerged in a recent study (Yetish et al., 2016) among primitive peoples in Africa and South America. These people live without any electricity and are therefore entirely driven by daylight and the seasonal temperatures. After all, they have no electrical lighting or central heating. Records were made of when they went to sleep and when they woke up, together with the ambient temperature and the amount of light. In the winter, they slept almost an hour longer than in the summer. The ambient temperature appeared to influence the moment they awoke more than the daylight. People usually woke up before it was light outside and at the exact moment that the ambient temperature began to rise.
In short: A great excuse to stay in bed for longer when it’s cold outside. ☺