Association between circadian physical activity patterns and cancer incidence through regulation of inflammation: A UK biobank study

Physical activity (PA) has been linked with cancer incidence. However, the effects and mechanisms underpinning circadian PA trajectories on cancer remain elusive. This study aimed to explore the optimal PA patterns in reducing cancer incidence and the associated potential mediators. Between 2006 and 2010, 502,400 participants were recruited from the UK Biobank. Out of these, 102,323 participants wore accelerometers, which allowed for collecting acceleration data continuously over 7 days. After excluding participants with previous cancer history, 96,687 participants were included in K-means cluster analysis to identify PA trajectories. The association between PA and cancer incidence was assessed using Cox regression analysis. Additionally, we investigated the mediating role of inflammation. A total of 5995 cancer cases were recorded during a median follow-up of 7.1 years. Four distinct PA trajectories (persistent low, single peak, double peak, and vigorous) were identified. The ideal PA patterns reduced the risk of 7 out of 17 site-specific cancers, with the lowest hazard ratios and 95% confidence intervals of cancer for bladder (0.59, 0.40-0.86), breast (0.73, 0.60-0.89), kidney (0.45, 0.26-0.78), lung (0.59, 0.41-0.84), myeloma (0.49, 0.27-0.88), and oral & pharynx (0.51, 0.26-0.98) in the vigorous pattern and for colorectal (0.71, 0.54-0.93) in the double peak pattern. Moreover, the mediating effects of inflammation were significant. Optimal PA trajectories reduced cancer incidence, especially in double peak and vigorous patterns. The protective effect was associated with both intensity and circadian rhythm. Crucially, this protection was mediated by inflammation regulation.