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.
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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.
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."