Heterogeneity in aging: exploring grip strength variability in population-based age-sex cohorts

Heterogeneity in aging refers to the increased variability in individual characteristics that occurs with age. Little is known about sex differences in heterogeneity in aging trends, or about longitudinal patterns of heterogeneity within age groups.

We used grip strength, a well-recognized measure of physical function, to explore patterns of variance in population-based age-sex groups cross-sectionally and longitudinally. We constructed a cohort from the UK Biobank database consisting of individuals aged 40-69 at first grip strength assessment and with a recorded follow-up grip strength assessment (N = 73 134; 52% female; assessment-reassessment interval, 4-18 years). In females and males separately, we compared, with and without covariates: (1) patterns of grip strength variance across successively older five-year age groups at initial assessment; (2) differences in grip strength variance between first and second assessments within the same age groups; (3) differences in grip strength variance between assessments when intervals were <10 years or ≥10 years.

Cross-sectional results revealed that, for females, grip strength variance did not differ significantly between pairs of successively older age groups; for males, grip strength variance decreased across successively older age groups. Longitudinal results showed that, for females, grip strength variance remained stable over time, whereas for males grip strength variance increased over time within nearly all age group cohorts. Covariates attenuated but did not eliminate these trends.

Heterogeneity in grip strength with aging operates differently in females and males, and patterns of heterogeneity for males are strikingly different depending on whether age is explored cross-sectionally or longitudinally.