"Hauling yourself out of bed when the sun hasn’t risen yet can be a very tough task. One of the reasons why this is difficult is because of our circadian rhythms. This refers to the physical, mental, and behavioral changes that follow a 24-hour cycle – processes that respond primarily to light and darkness," says Theresa.
It's all to do with our production of melatonin – a hormone that makes you sleepy. Sunlight suppresses the production of melatonin, and darkness has the opposite effect. "When it is totally dark, we lose the strong wake-up cue that sunlight gives us, which leads us to battle biology in order to switch into alertness," she continues.
A lack of vitamin D – the vitamin we get from sunlight – might also have an effect. "Vitamin D intake typically decreases drastically in the winter due to fewer hours of sunlight, which studies have suggested can lead to insufficient sleep," says Theresa.