What is circadian rhythm?

Health, Science 2017-10-10

Circadian rhythm is integral to our functioning; yet many have never heard of the phenomenon, or don’t know why it’s so significant. With the 2017 Nobel Prize in Physiology or Medicine having recently been awarded to Jeffrey C. Hall, Michael Rosbash and Michael W. Young for their “discoveries of molecular mechanisms controlling the circadian rhythm”, perhaps this will be the year circadian rhythms reach the science spotlight.

So what exactly is circadian rhythm, and why did the researchers exploring it deserve the Nobel Prize?

Circadian rhythm is essentially our body clock; the approximately 24-hour rhythm that occurs in cellular processes in almost every tissue of the body. The 24-hour rhythmicity of the circadian system is driven by environmental time cues, such as the natural day and night light cycle, cycles of rest and activity, and even feeding behaviour. Our bodies then translate these timing cues into molecular oscillations within individual cells to drive our functioning.

Circadian rhythm is controlled by the suprachiasmatic nucleus (SCN), a small area in the centre of the brain. The SCN is not actually required for peripheral organs to generate their own rhythms. Rather, it acts more like the conductor of an orchestra, guiding each organ to oscillate in the ideal phase for that specific tissue.

Intrinsic circadian clocks are evolutionarily conserved across the animal kingdom, with organisms as small and as ancient as cyanobacteria exhibiting the same clock systems as us humans. In experiments using fruit flies, the 2017 Nobel Prize laureates identified several of the genes that made up this core molecular clock that controls daily biological rhythm.

This includes the period gene, which encodes the protein PER. They discovered that PER accumulated in the nucleus of cells during the night, and degraded during the day, causing rhythmic 24-hour oscillations. Beyond this first discovery, the team went on to identify that these oscillations were auto-regulatory, meaning that they continuously self-regulate their levels in a cyclic fashion.

With many of our genes coordinated by the circadian clock, the impact they have on our complex physiology is vast. Circadian research since the initial discoveries by this year’s Nobel laureates has exposed how disruptions to our circadian system, for example nocturnal lifestyle, working night shifts, and jet lag, can cause an array of problems with sleep, behaviour, body temperature and metabolism, and even impact cancer.

Circadian disruption therefore imposes a major public health issue that has yet to receive the recognition it deserves. One can only hope that the awarding of the Nobel Prize to circadian researchers will increase public awareness of the circadian influences on health risks, leading to enhanced lifestyle choices that improve the alignment of physiological systems with the daily body clock.

Tori Blakeman

Tori Blakeman is PR Account Manager & Writer at Notch. Follow her on Twitter @ttttor.

For more information on circadian clocks and their implication in breast cancer, read Tori’s review in Breast Cancer Research.

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