Asked by: Luke Davison, East Grinstead

If you spend time in the sunshine, your body must expend energy to prevent you from overheating. One way it does this is to sweat, which leads to lethargy and dehydration if you don’t drink enough. The more you exert yourself, the more work your body has to do to control your temperature, which makes everything feel like an effort.

The cold makes people feel tired for the opposite reason, as the body must consume energy to stay warm, including through shivering. Bear in mind, though, the Sun doesn’t only make you feel tired. By influencing your circadian rhythm – the body’s internal clock – it also helps you get up in the morning.

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Authors

Christian Jarrett
Christian Jarrett

Dr Christian Jarrett is a cognitive neuroscientist, science writer and author. He is the Editor of Psyche, the sister magazine to Aeon that illuminates the human condition through psychology, philosophy and the arts. Jarrett also created the British Psychological Society's Research Digest blog and was the first ever staff journalist on the Society's magazine, The Psychologist. He is author of Great Myths of The Brain and Be Who You Want: Unlocking the Science of Personality Change.

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