Nocturnal tissue glycemia is associated with cortisol rise in the morning in young but not in older healthy adults

Cortisol and vitamin D are known to influence plasma glucose, but their relationship with glycemia, assessed by continuous glucose monitoring, remains unclear for healthy adults. This study compared these relationships between 32 young (26.0 ± 4.8 years) and 25 older (67.3 ± 4.8 years) healthy volunteers. Cortisol was determined at bedtime, awakening, and 30 min (T30) and 60 min (T60) post-awakening. Older adults had higher fasting glucose but lower cortisol concentration at T30 than young adults. In young adults, night- and daytime mean glucose and fasting glucose correlated negatively with cortisol at T30, while glycemic variability correlated positively with cortisol at T60. Vitamin D correlated negatively with nighttime mean glucose in the young group. In conclusion, glucose concentration and glycemic variability are associated with the cortisol response the following morning. The lack of these associations in older adults could be explained by their higher fasting glucose concentrations resulting in a lower morning cortisol response.