Intrinsic capacity and loneliness, according to sex, in an upper-middle income country: insights from the ELSI-Brazil cohort.

Objectives: To investigate the association between loneliness and intrinsic capacity, a multidimensional indicator of healthy ageing, in Brazilians aged ≥50 years.

Method: This cross-sectional study used baseline data from 7,123 participants of the nationally representative Brazilian Longitudinal Study of Aging (ELSI-Brazil) (2015-2016). Intrinsic capacity (IC) (sensory, mobility, psychological, cognitive, and vitality), was determined using a validated composite z-score (higher scores = better capacity). Loneliness comprised a single-item. Quantile regression models were stratified by sex after adjusting for sociodemographic, and health characteristics.

Results: The median IC were lower in women than in men (-0.54 vs. 0.69, respectively). Loneliness was related to lower IC composite z-scores in both sexes, demonstrating stronger associations at lower quantiles. The IC composite z-score decreased in those experiencing severe loneliness, both in women (quantile 0.75: β = -0.39; 95% CI = -0.47 to -0.31) and men (β = -0.36; 95% CI = -0.54 to -0.17). However, mild loneliness was associated with worse IC among men only at quantile 0.25 (β = -0.12; 95% CI = -0.23 to -0.01), different from women.

Conclusion: Loneliness was associated with worse IC. Cross-sectional design limits causal inference, but supports that community engagement, social support, and accessible environments are crucial for promoting healthy ageing in both sexes.