Much to our dismay, the days are much shorter in winter, meaning there is less sunlight (and heat) to enjoy. This lack of sunlight can also affect our hormones (in particular our sleep hormones) and some people may develop seasonal affective disorder.”When we are seeing less daylight, our pineal glands respond to the lack of sunshine by producing melatonin, the sleep hormone that can make use feel ready to sleep,” Dennaoui explained.