Internal Circadian Misalignment of the Human Metabolome Links Night Shiftwork to Metabolic Impairment

Circadian misalignment, as experienced during shiftwork, impairs glucose metabolism and body weight regulation, yet the underlying biochemical mechanisms remain incompletely understood. Characterizing how circadian misalignment alters circulating metabolites provides a promising avenue to help identify these mechanisms. Although data from metabolomics studies have identified circulating metabolites with daily rhythms, it is not comprehensively known which rhythms shift during circadian misalignment and whether such shifts relate to metabolic impairment. We conducted 24-hour (h) metabolomic profiling every 4 h in 14 healthy adults (8 women) aged 26.4 ± 1.2 years (mean ± SD), undergoing a 6-day simulated night-shiftwork protocol. 24-h modeling analyses identified metabolite rhythms influenced by circadian versus behavioral cycles (sleep, food intake) and quantified internal circadian misalignment using acrophase shifts. Metabolic outcomes included glucose homeostasis (test meals) and energy expenditure (EE; whole-room calorimetry). Night-shiftwork produced widespread alterations in metabolite rhythms, with significant internal misalignment in multiple metabolites across pathways including pyrimidine metabolism, bile acid-microbiome signaling, and lipid metabolism. During misalignment, glucose and insulin area under the curve increased (p < 0.05) and EE decreased (p < 0.05). Internal misalignment of uridine and glycoursodeoxycholic acid was associated (p < 0.05) with impaired glucose tolerance, while their circulating concentrations were associated with decreased EE. Misalignment of uridine and glycoursodeoxycholic acid suggests dysregulated pyrimidine and bile acid-microbiome pathways as potential mechanisms linking circadian misalignment to cardiometabolic disease risk.