How are HbA1c and fatigue related?

HbA1c (glycated hemoglobin) reflects average blood glucose over 2–3 months. Elevated HbA1c (>6.5 %) indicates diabetes or prediabetes. Chronically high glucose can cause fatigue through dehydration (polyuria), impaired cellular energy metabolism (insulin resistance), and low-grade inflammation. Nocturnal hyperglycemia or hypoglycemia (e.g., from medications) disrupts sleep and leads to daytime tiredness. Conversely, a very low HbA1c (e.g., <5.0 %) may signal frequent hypoglycemia, which also causes exhaustion. The evidence for this link is clinically well-established (human-strong), based on observational studies and pathophysiology. However, fatigue is multifactorial (iron deficiency, thyroid, sleep apnea, stress). A single HbA1c value alone does not diagnose fatigue. Interpretation requires clinical context. The provided context lacks specific studies on this topic, so the answer relies on general medical knowledge.