Beneath the veneer of our super-sophisticated 21st-century existence, there lies a very basic truth: our lives are fundamentally governed by daily biological cycles called circadian rhythms.

These rhythms dictate the best time for us to eat, drink, sleep, have sex and even to get vaccinations. And we defy them at our peril.

Mounting evidence shows how our modern electrically illuminated life, which knocks off kilter the natural cycle of exposure to sunlight and darkness, vastly raises the risk of illnesses such as heart disease and obesity.

The basic mechanism of our circadian rhythms — or the body clock as they are more popularly known — was revealed three decades ago. But only this week has the highest scientific recognition, in the form of the Nobel Prize, been awarded to the three American scientists who discovered it: Jeffrey Hall, Michael Rosbash, and Michael Young.

It’s taken that long for the scientific community to appreciate fully the astonishing importance of circadian rhythms. Indeed, body clocks lie at the core of our existence. Here, JOHN NAISH reveals what makes us tick. In 1984, the three scientists identified a gene that runs the 24-hour biological clock inside humans. It ensures that our bodies stay in sync with the revolutions of the Earth and the shifts between day and night.

The researchers bred fruit flies that lacked this gene and found the insects were unable to control their most basic biological functions such as blood pressure, heart-rate, temperature, hormone levels, metabolism, sleep, and even behaviour.

‘This mechanism has its fingers in every aspect of physiology and behaviour that humans undergo,’ Professor Rosbash explained this week. Researchers at the universities of Bath and Surrey recently reported the discovery of circadian clocks in our muscles which, if disrupted, may be linked to the development of Type 2 diabetes.

They found that the muscle clocks are involved in regulating how the body responds to insulin — a hormone that promotes the uptake of glucose from the blood.

Poor quality sleep — known to increase the risk of Type 2 diabetes — may disrupt the muscle clocks and help to trigger insulin-resistance, leading to high blood sugar levels that are characteristic of the disease. One possible evolutionary reason for the existence of larks and owls is that it enabled our tribal ancestors to ensure there were suitably alert guards around their camps, night and day.

Being a morning or an evening person appears to be linked to the hour of our birth.

A study of thousands of U.S. students found that those born in the morning scored better in IQ tests held in the morning and thus were larks. Those born later in the day did better in tests held late in the afternoon and thus were owls.

Our body clocks may be set when, as babies, we are first exposed to the light of the world.