Irish Journal of Medical Science, June 2026 | Kevser Gürsan et al., Uşak University
Metabolic health doesn’t operate on its own. New research from Türkiye finds that fatigue and slowed reflexes begin appearing in adults with prediabetes, a metabolic state that can precede type 2 diabetes by years. Cognitive performance takes a further hit among those with uncontrolled type 2 diabetes.
Researchers at Uşak University tested 94 adults aged 60 and older, sorted into four groups by hemoglobin A1c level: healthy, prediabetes, controlled type 2 diabetes (blood sugar within the target range), and uncontrolled type 2 diabetes (blood sugar above the target range). Each participant completed standardized tests of attention, memory, mobility, reflex speed, and fatigue.
Fatigue scores were significantly higher in every group with elevated blood sugar, including prediabetes, compared to healthy participants. The prediabetes group also showed slower foot reaction time, a measure of how quickly the nervous system responds to a physical cue. Adults with uncontrolled diabetes had the lowest cognitive scores, particularly in attention and delayed recall. These differences remained after researchers adjusted for age, weight, education, and other health conditions.
The underlying mechanism is well-documented. Chronic high blood sugar damages small blood vessels, including those feeding the brain. As Jose Luchsinger, a Columbia University professor of medicine who was not involved in the study, has explained, “diabetes causes cerebrovascular disease—that is, vascular disease in the brain.” That damage compounds over years, disrupting regions responsible for attention and memory.
The findings reinforce a broader theme in health research: the body’s systems are linked. What happens in one system tends to affect others. According to this new research, fatigue and slower reflexes aren’t just signs of a long day—they can be some of the earliest signals blood sugar is sending, well before a diagnosis arrives.
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