Diurnal cortisol cycle and cognitive performance in older people with Type 2 diabetes

In older adults with Type 2 Diabetes (T2D), hypothalamic-pituitary-adrenal (HPA) axis dysregulation accompanied by cognitive impairment has been reported. While the impact of HPA function on declarative memory (DM), working memory (WM), and executive function (EF) has received increased attention in aging research, its role in T2D remains largely unexplored. This study compared diurnal cortisol patterns and cognitive performance between 51 patients with T2D treated with oral antidiabetic medications, injectable therapies, or a combination of both, and 51 healthy controls matched for age, sex, educational level and, body mass index. Participants completed a battery of neuropsychological tests and the Beck Depression Inventory (BDI-II). Additionally, they provided four saliva samples per day across two weekdays to assess the cortisol awakening response (CAR) and the diurnal cortisol slope (DCS). Group comparisons (T2D vs. controls) and moderation analyses were conducted to assess group differences and the associations between cortisol indices and cognitive performance, with group or depression included as moderators. T2D patients showed poorer performance than healthy controls, particularly on DM and WM, but no significant differences in CAR or DCS. In controls, a higher CAR was related to lower Stroop interference, although no significant relationships were found in T2D patients. Across the entire sample, CAR was negatively associated with Stroop interference at low and moderate depression levels, while DCS was positively associated with RAVLT delayed recall at low levels of depression. Our results indicate that medically treated T2D patients show poorer cognitive performance than healthy controls; however, cortisol does not seem to contribute to these cognitive deficits. These findings add to the limited literature on the impact of the HPA on cognitive function in T2D older adults, and they encourage future studies to delve into the mechanisms that could influence cognitive performance in this population, as well the relevance of depression in these cognitive deficits.