OBJECTIVES: To investigate the effect of omega-3 (ω-3) polyunsaturated fatty acid supplementation and a multidomain intervention (MI) (physical activity counselling, cognitive training and nutritional advice) among community-dwelling older adults on levels of intrinsic capacity (IC), a construct recently proposed by the World Health Organization. STUDY DESIGN: Secondary analysis from the factorial-design 3-year Multidomain Alzheimer Preventive Trial (MAPT) with 1445 subjects (64.2 % female, mean age 75.3 years, SD = 4.4) randomized to one group of MI plus ω-3 (800 mg docosahexaenoic acid and 225 mg eicosapentaenoic acid/day); MI plus placebo; ω-3 supplementation alone; or placebo alone. Data collection was held between 2008 and 2014. MAIN OUTCOME MEASURES: IC domains were examined with the Geriatric Depression Scale (psychological); Short Physical Performance Battery (mobility); Z-score combining four tests (cognitive function); and handgrip strength (vitality). All domains were combined into a composite IC Z-score. RESULTS: After 3 years, IC Z-score decreased among all groups when time was considered continuous (MI plus ω-3: -0.16, 95 %CI: -0.22 to -0.10; MI alone: -0.13, 95 %CI: -0.19 to -0.07; ω-3 alone: -0.19, 95 %CI: -0.25 to -0.10; placebo: -0.20, 95 %CI: -0.26 to -0.14; all p < 0.0001). There were no significant differences between groups. In a sensitivity analysis with categorical time, significant within-group declines were first identified at 24 months for all groups. CONCLUSIONS: This trial designed to improve cognitive function was unable to find effects of the intervention on the composite IC Z-score. Further investigations are needed, especially trials providing stronger interventions (such as exercise training and a controlled diet) and also embracing the sensorial domain of IC.