Understanding chronobiology - the study of biological rhythms - can help nurses care for their patients and themselves. This article discusses the internal and external factors which affect the body’s daily rhythms, and the effectiveness of different drugs and procedures at certain times of the day. The author also offers advice for nurses anticipating night work to minimise disruption to their own circadian rhythm

It is now well established that all human physiological processes exhibit rhythmicity. The menstrual cycle is probably the best-known, but physiological variables, such as body temperature, blood pressure, hormone secretion and renal excretion, have also been shown to have a regular circadian pattern over a period of around 24 hours (Minors and Waterhouse 1981) (Figs. 1-4). Definitions associated with chronobiology are given in Box 1.