If you've ever woken up feeling decades older than you should, it could be down to your body clock. Stiff and achey joints are a common problem, particularly as we get older, and it tends to be worse in the morning as our body hasn't started producing its own natural 'ibuprofen' yet.
See also: Seven foods to ease the pain of arthritis
See also: What you can do to ease joint pain
According to a study from the University of Manchester, the body releases an anti-inflammatory protein which naturally combats stiffness, but it only kicks into gear when we're awake.
Researchers took samples from spinal discs and found that they have their own 24-hour body clock - so waking up with a stiff back could simply mean you got out of bed before your spine thinks it's daytime.
As a result, getting a good night's sleep could help protect the body clock and avoid getting disc problems later in life.
Lead researcher Dr Qing-Jun Meng said: "It's been known for years that, as a consequence of the daily activity and resting cycle, we are taller in the mornings by up to 2cm more than when we go to bed.
"The discovery of body clocks in the disc may go some way to explain for the first time the science behind this rhythmic physiology of the spine. Our research shows this system is regulated by our internal body clock and when the body clock ceases to work properly during ageing or in shift workers, lower back pain is more likely. Looking after your body clock will help manage or delay the onset of your back pain."
Dr Natalie Carter, of Arthritis Research UK, which funded the study, said: "This research is a significant breakthrough in our understanding of lower back pain.
"Many people find that their symptoms get worse at certain times of the day and the results of this study reveal a likely biological basis to this effect.
"An exciting prospect is it may be possible to use this new information to improve treatments and pain relief for people affected by this debilitating condition."