Context: The timing of sleep, physical activity, and dietary intake show variation over the week, with different timings in the weekend compared to the weekdays, which may potentially lead to impaired glucose and lipid regulation on Mondays compared to other weekdays.

Objective The aim of the study was to investigate differences in glucose metabolism and fasting triglyceride concentrations on Mondays compared to the rest of the week.

Design, setting and participants This cross-sectional study is based on data from the Maastricht Study, including 6067 participants without known diabetes and 1568 previously diagnosed with type 2 diabetes.

Main outcome measures Confounder-adjusted linear regression analysis was applied to study the associations of day of the week of examination with glucose and insulin responses to an oral glucose tolerance test and fasting triglyceride concentrations.

Results In fully confounder-adjusted models, mean (95% CI) concentrations of fasting glucose, insulin, and triglycerides were slightly higher on Mondays compared with the other weekdays [glucose: 1% (0-2); insulin: 9% (1-18); triglycerides: 5% (2-8)]. Interaction analyses revealed that the association of weekday with insulin was only pronounced in men [18% (3-35)], but not in women [1% (-8-10)], whereas the associations with glucose and triglycerides were only apparent for individuals with known type 2 diabetes [glucose: 4% (0-7); triglycerides: 14% (6-23)] compared to the background population [glucose: 0% (0-1); triglycerides: 3% (0-6)].

Discussion Being examined on a Monday was associated with higher fasting insulin concentrations among men but not women.