The objective is to assess the association, adjusted by sex and age, between the body mass index (BMI) and cognitive or physical functioning, and depression in Mexican elderly. Method: Three hundred and ninety five (female: 71.6%) subjects aged ≥ 60 were recruited from three independent senior care centers. Body composition was stratified as underweight, normal, or overweight (World Health Organization criteria). Cognitive functioning (Short Portable Mental State Questionnaire-SPMSQ); independent physical functioning (Barthel Index of Activities of Daily Living - BIADL); and level of depressive symptoms (Geriatric Depression Scale - GDS) were also measured. The independent and interactive effects of BMI, sex, and age on cognitive/ physical functioning, and depressive symptoms were analyzed. Results: Univariate analyses showed that underweight elderly performed worse (SPMSQ: 4.50[2.84]; BIADL: 55.00[15.99]) than normal (SPMSQ: 6.46[2.86], p≤0.05; BIADL 83.40.00[18.81], p≤0.001) and overweight (SPMSQ: 7.82[2.21], p≤.0001; BIADL: 84.42.00[15.44], p≤.0001) in cognition and physical functioning. Additionally, in underweight elderly, depression level was significantly higher (GDS: 3.90[2.28]) than the scored by overweight (GDS: 2.13[1.68], p≤0.01). Significant differences by sex were only found for physical functioning. Age-related analysis showed that the oldest subgroup was significantly more affected than the young old and the middle old in cognitive and physical functions, besides depression cores. Analysis of the interactions of BMI with sex and age did not show significant effect for any of the studied outcome variables. Conclusions: In Mexican elderly people, the presence of underweight was associated to impair cognitive/ physical functions and higher depression scores. This seems to be independent to the association between higher age and the same variables.
