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Objective Telomere length (TL) is an indicator of cellular ageing, with patients with severe mental disorders tending to have shorter telomeres than the general population. Coffee consumption may reduce oxidative stress, helping prevent biological ageing processes like telomeric shortening. The UK National Health Service advises limiting caffeine intake to 400 mg/day (4 cups of coffee). However, the role of coffee consumption and TL in psychiatric populations remains unclear.Methods This cross-sectional study included 436 participants (schizophrenia spectrum (n=259) and affective disorders (n=177)) from the Norwegian TOP study. Leucocyte TL was measured via blood using quantitative real-time polymerase chain reaction (qPCR). Patients self-reported coffee consumption, quantified as cups per day (no coffee, 1–2, 3–4, 5+).Results An inverted J-shape was found between TL and coffee intake, peaking at 3–4 cups/day before declining after 4 cups (F=3.29, p=0.02). The largest TL difference was between those drinking the highest recommended dose and non-drinkers (F=6.13, p=0.01). Coffee drinkers within the recommended dose had longer TL, comparable to 5 years younger biological age, adjusted for confounders.Conclusion Coffee intake within the recommended dose is linked to longer telomeres in severe mental disorders, comparable to 5 years younger biological age.