%0 Journal Article %A Gustav Nilsonne %A Mats Lekander %A Torbjörn Åkerstedt %A John Axelsson %A Michael Ingre %T Diurnal variation of circulating interleukin-6 in humans: a meta-analysis %D 2016 %R 10.1101/042507 %J bioRxiv %P 042507 %X The pleiotropic cytokine interleukin-6 (IL-6) has been proposed to contribute to circadian regulation of sleepiness by increasing in the blood at night to signal for sleepiness. Earlier studies have reported diurnal variations of IL-6, but phase estimates are conflicting. We have therefore performed a meta-analysis on the diurnal variation of circulating IL-6. Studies were included if they reported circulating levels of IL-6 recorded at least twice within 24 hours in the same individual. A systematic search resulted in the inclusion of 43 studies with 56 datasets, for a total of 1100 participants. Individual participant data were available from 4 datasets with a total of 56 participants. Mixed-effects meta-regression modelling confirmed that IL-6 varied across the day. Contrary to many previous claims, we found that the most consipuous effect was a trough in the morning, rather than a peak in the evening or night. We propose that the diurnal variation of IL-6 may be explained to some degree by suppression of IL-6 secretion by the morning Cortisol peak. %U https://www.biorxiv.org/content/biorxiv/early/2016/03/05/042507.full.pdf