Scientists have discovered why we wake up stiff in the morning - because our body's natural ibuprofen has not kicked in yet.
Researchers revealed the reason our limbs can feel rigid and achy when we rise is because the body's biological clock suppresses anti-inflammatory proteins during sleep.
When we start moving around each morning our body is playing catch up as the effects of the proteins wear off.
The research by scientists at Manchester University could help develop drugs to treat inflammatory diseases such as arthritis.
Dr Julie Gibbs, a researcher at the Centre for Endocrinology and Diabetes at the University of Manchester's Institute of Human Development, said: "By understanding how the biological clock regulates inflammation, we can begin to develop new treatments, which might exploit this knowledge.
"Furthermore, by adapting the time of day at which current drug therapies are administered, we may be able to make them more effective."
Dr Gibbs and her colleagues harvested cells from joints of healthy mice and humans that are important in the pathology behind inflammatory arthritis.
Each of the cells was found to have a 24-hour rhythm, and they were altered to disrupt the rhythm by knocking out the cryptochrome gene.
This led to an increased inflammatory response suggesting its product, the cryptochrome protein, has significant anti-inflammatory effects.
When drugs were given to activate the protein, the researchers found it protected against inflammation. The discovery could lead to the development of new drugs for arthritis.
The researchers also exposed arthritic mice to constant light and found the mammals had no daily variation in inflammation as normally seen.
The study is published in the Federation of American Societies for Experimental Biology journal.
Dr Thoru Pederson, editor-in-chief of the FASEB journal, added: "The clinical implications are far-reaching."
Researchers at the University of Manchester also found this month that discs in the spine have 24-hour body clocks, which when they do not work properly can contribute to lower back pain.
Over 80 per cent of British people are expected to suffer back pain during their life times, with the condition being more likely in old age, in part because of the progressive degeneration of the spine dis.
The study published in Annals of the Rheumatic Diseases suggested that getting a good night's sleep by avoiding night working and rotating shift work could protect the body clock and help to avoid problems with back pain later in life.
Dr Qing-Jun Meng, a Senior Research Fellow funded by Arthritis Research UK, said: "It has 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 that 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 to become an issue."