circadian rhythm
(sir-KAY-dee-un RIH-thum)
The natural cycle of physical, mental, and behavior changes that the body goes through in a 24-hour cycle. Circadian rhythms are mostly affected by light and darkness and are controlled by a small area in the middle of the brain. They can affect sleep, body temperature, hormones, appetite, and other body functions. Abnormal circadian rhythms may be linked to obesity, diabetes, depression, bipolar disorder, seasonal affective disorder, and sleep disorders such as insomnia. Circadian rhythm is sometimes called the “body’s clock.”