Clocking in: chronobiology in rheumatoid arthritis.

Circadian rhythms are of crucial importance for cellular and physiological functions of the brain and body. Chronobiology has a prominent role in rheumatoid arthritis (RA), with major symptoms such as joint pain and stiffness being most pronounced in the morning, possibly mediated by circadian rhythms of cytokine and hormone levels. Chronobiological principles imply that tailoring the timing of treatments to the circadian rhythm of individual patients (chronotherapy) could optimize results. Trials of NSAID or methotrexate chronotherapy for patients with RA suggest such an approach can improve outcomes and reduce adverse effects. The most compelling evidence for RA chronotherapy, however, is that coordinating the timing of glucocorticoid therapy to coincide with the nocturnal increase in blood IL-6 levels results in reduced morning stiffness and pain compared with the same glucocorticoid dose taken in the morning. Aside from optimizing relief of the core symptoms of RA, chronotherapy might also relieve important comorbid conditions such as depression and sleep disturbances. Surprisingly, chronobiology is not mentioned in official guidelines for conducting RA drug registration trials. Given the imperative to achieve the best value with approved drugs and health budgets, the time is ripe to translate the 'circadian concept' in rheumatology from bench to bedside.