Abstract
Sleep irregularity, characterized by inconsistent sleep patterns from day to day, has become increasingly prevalent in today's 24/7 society. As a key component of multidimensional sleep health, the potential impact of sleep irregularity on cardiometabolic disease and mortality has recently received attention in research. In this review, we summarize the current evidence from epidemiological, clinical, and mechanistic studies to highlight the role of sleep irregularity in obesity, metabolic syndrome, diabetes, cardiovascular disease, and mortality. We focus on recent large prospective studies that establish stronger temporal relationships between sleep irregularity and cardiometabolic disease risk and mortality, compared with earlier cross-sectional studies. The preponderance of evidence supports that sleep irregularity is a robust risk factor for these conditions, and in some cases, may be a more significant predictor than other widely studied sleep factors, such as sleep duration. We propose potential biological, behavioral, and psychological pathways through which sleep irregularity may contribute to the development of cardiometabolic disease. We also discuss key limitations in the current literature, including the lack of standardized measures for assessing sleep irregularity, the scarcity of intervention studies to clarify its real-world implications, and the incomplete understanding of the underlying mechanisms. Addressing these gaps through further studies could pave the way for more effective clinical and public health strategies aimed at reducing sleep irregularity and ultimately mitigating the risk of cardiometabolic diseases and mortality.