Most life on Earth displays biological processes that follow an endogenous (internally-regulated) rhythm of around 24 hours. This rhythm is based on an internal biological clock, but is also entrained by environmental cues, such as light and temperature, that is, reset, synchronised or adjusted by these external cues as occurs when we travel across time zones. Jet lag, for example, denotes the time it takes the body to readjust its circadian rhythm to fall into sync with the new environmental cues. It has been shown that the success of transplants and other medical treatments may be increased through added consideration of the body’s circadian rhythm. Also, with regards to pharmaceuticals, there is often a strong circadian regulation of the target of a particular drug, often a certain protein expression that the pharmaceutical drug seeks to inhibit. Therefore, if the expression does not become active until the evening, but the drug is taken in the morning, it will have no effect or will require an increasingly heavy dose before it has an effect, which also increases the side effects. If, however, the drug can be timed to match the peak expression of the target, then less of the drug will be required to maximise efficacy, while reducing potential side effects associated with the drug. This field of study is called chronotherapeutics and aims to reduce adverse reactions to medical interventions as well as increasing their efficacy.
We evolved to be diurnal creatures. That is why we are at our most active during daylight hours, hunting for food and eating, while we are equipped to store this energy intake to cover the rest of the day and night when we are not eating. When our circadian rhythm is balanced between a distinct biological day and a biological night, the body is able to optimally assign activities to one mode or the other. Brain wave activity, immune function, hormonal production, autophagy, metabolic processes and cell regeneration all oscillate according to the distinct day and night modes of the circadian rhythm. For example, cellular repair, rest, brain development and memory processing are best suited to the night-time mode, while mental alertness, digestion, immune resilience and glucose availability are most needed during the day. A vital function of circadian oscillations in the body is to provide the crucial repair time required to mend the daily damage caused just from being alive, active and breathing.
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