How the time of day can increase the risk of dying from an irregular heartbeat has been identified by researchers. The risk of "sudden cardiac death" peaks in the morning and rises again in the evening. A study published in the journal Nature suggests that levels of a protein which controls the heart's rhythm fluctuates through the day. A body clock expert said the study was "beautiful". The inner workings of the body go through a daily routine known as a circadian rhythm, which keeps the body in sync with its surroundings. Jet lag is the result of the body getting out of sync. As the chemistry of the body changes throughout the day, this can impact on health. US researchers say they have identified, in mice, how the time can affect the risk of sudden cardiac death, which kills 100,000 people a year in the UK. 'Insights' They identified a protein called kruppel-like factor 15 (Klf15), which was controlled by the body clock and whose levels in the body went up and down during the day. The protein influences ion channels which control heart beat. Genetically modified mice which produced too much Klf15 and those which produced none at all both had an increased risk of developing deadly disturbances in cardiac rhythm. Prof Darwin Jeyaraj, from the Case Western Reserve University School of Medicine, said: "Our study identifies a hitherto unknown mechanism for electrical instability in the heart. "It provides insights into day and night variation in arrhythmia susceptibility that has been known for many years." There are important differences in the way that human and mouse hearts work, so it is unknown whether the same mechanism exists in people. Fellow researcher Prof Mukesh Jain said: "We are just scratching the surface. It might be that, with further study, assessment of circadian disruption in patients with cardiovascular disease might lead us to innovative approaches to diagnosis, prognosis, and treatment." Dr Michael Hastings, from the Medical Research Council's Laboratory of Molecular Biology, told the BBC: "It's a great paper, it gives a beautiful molecular mechanism which explains a phenomenon that's been kicking around for a long time." He said translating the findings into medicine was all about "targeting the most vulnerable stage" such as slow-release blood pressure drugs, which become active first thing in the morning when the risk is highest. "When you think about it, it's so blooming obvious," he added.