Association between chronotype, glucose metabolism and type 2 diabetes at population level - A systematic review

A chronotype is an expression of an individual circadian rhythm associated with sleep and physical activity. It categorizes people as morning, intermediate and evening chronotype. The aim of this systematic review was to evaluate the association of chronotype with glucose metabolism at population level.. The study was conducted in accordance with the international PRISMA Code of Systematic Reviews. Covidence was used for data selection. We included articles that utilized data from unselected populations. Articles were excluded primarily based on the characteristics of the study population, including shift workers, patients with specific disease and children. Finally, there were a total of ten articles that met the eligibility criteria. Eight studies had a cross-sectional setting, and three had prospective study design. Seven out of ten articles reported a statistically significant association between evening chronotype and glucose metabolism disorders. The number of participants in the studies varied (N=447 to 360,403). Parameters used to examine glucose metabolism were diabetes, prediabetes, fasting glucose, fasting insulin, Hemoglobin A1c (HbA1 c), Homeostatic Model Assessment for Insulin Resistance (HOMA-IR), and two hours oral glucose tolerance test. Based on the current literature, the evening chronotype appears to be positively associated with adverse changes in glucose metabolism, such as increased fasting glucose and insulin resistance, as well as type 2 diabetes. In the future, it might be necessary to further study the association between chronotype and glucose metabolism. Longitudinal analyses are needed in large research populations in order to verify the existence of the association.