Background: Cognitive decline, a common process of brain ageing, has been associated with telomere length (TL). Delving into the identification of reliable biomarkers of brain ageing is essential to prevent accelerated cognitive impairment.

Methods: We selected 317 non-smoking 'Prevención con Dieta Mediterránea-Plus' (PREDIMED-Plus) participants (mean age, 65.8 ± 5.0 years) with metabolic syndrome from two trial centres who were following a lifestyle intervention. We measured TL and cognitive function at baseline and after 3 and 4 years of follow-up, respectively. Associations between baseline or 3-year changes in TL and baseline or 4-year changes in cognitive function were analysed using multivariable regression models.

Results: Baseline TL was not associated with baseline cognitive performance. Nevertheless, longer baseline TL was associated with improved 4-year changes in the Executive Function domain (β: 0.29; 95%CI: 0.12 to 0.44; P < 0.001) and the Global Cognitive Function domain (β: 0.19; 95%CI: 0.05 to 0.34; P = 0.010). Besides, a positive association was found between longer baseline TL and improved 4-year changes in the animal version of the Verbal Fluency Test (β: 0.33; 95%CI: 0.12 to 0.52; P = 0.002). By contrast, 3-year changes in TL were not associated with changes in cognitive function after 4 years.

Conclusions: Longer baseline TL could protect from cognitive decline and be used as a useful biomarker of brain ageing function in an older Mediterranean population at risk of cardiovascular disease and cognitive impairment.