The Circadian Rhythm The circadian rhythm is a kind of body-clock which regulates our body functions such as sleepiness, body temperature, hunger and alertness. Plants and animals have a circadian rhythm as well. Our body relies on the predictable cycle of light end dark to synchronise our body-clock. Therefore jet-lag breaks down our circadian rhythm because we loose the cycle mentioned before, causing tirediness and sleep problems. It's interesting to note that our clock oscillates at its own endogenous period, even if we were put into a dark cave. In addition, exercise, food and caffeine can modulate our sleep pattern, although they are not as strongly as the light and dark cycle. In conclusion, adjusting the circadian rhythm correctly makes us feel better, avoiding sleep problem.