Beauty sleep could be real, say scientists who have explained for the first time why having a good night's sleep could actually prepare us for the rigours of daily life.
Published in the journal Nature Cell Biology, the study in mice shows how the body clock mechanism boosts our ability to maintain our bodies when we are most active.
Because we know the body clock is less precise as we age, the discovery may one day help unlock some of the mysteries of ageing, said Professor Karl Kadler from the University of Manchester in the UK.
The discovery shines light on the body's extracellular matrix, which provides structural and biochemical support to cells in the form of connective tissue such as bone, skin, tendon and cartilage.
Over half of our body weight is matrix, and half of this is collagen -- and scientists have long understood it is fully formed by the time we reach the age of 17.
However, the researchers have now discovered there are two types of fibrils -- the rope-like structures of collagen that are woven by the cells to form tissues.
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Thicker fibrils measuring about 200 nanometres in diameter are permanent, and stay with us throughout our lives, unchanged from the age of 17.
One the other hand, thinner fibrils measuring 50 nanometres are sacrificial, breaking as we subject the body to the rigours of the day but replenishing when we rest at night.
The collagen was observed by mass spectrometry, and the mouse fibrils were observed using state of the art volumetric electron microscopy every four hours over two days.
When the body clock genes where knocked out in mice, the thin and thick fibrils were amalgamated randomly, the researchers said.
"Collagen provides the body with structure and is our most abundant protein, ensuring the integrity, elasticity and strength of the body's connective tissue," said Kadler.
"It's intuitive to think our matrix should be worn down by wear and tear, but it isn't and now we know why: our body clock makes an element which is sacrificial and can be replenished, protecting the permanent parts of the matrix," he said.
Kadler said just like people need to oil a car and keep its radiator topped up with water, the thin fibrils help maintain the body's matrix.
"Knowing this could have implications on understanding our biology at its most fundamental level. It might, for example, give us some deeper insight into how wounds heal, or how we age," he said.