Age-Specific Effects of Epigenetic Aging and Calf Circumference on Adult Mortality

Background

Epigenetic clocks, particularly GrimAge and GrimAge2, are among the strongest molecular predictors of mortality. Skeletal muscle, reflected by calf circumference (CC), is also a critical determinant of survival in aging. However, it remains unclear whether muscle reserve modifies the relationship between epigenetic aging and mortality. We examined how GrimAge-based epigenetic aging and CC interact to shape survival across different life stages.

Methods

We analyzed 2,180 adults aged ≥50 years from the 1999–2002 U.S. National Health and Nutrition Examination Survey, with mortality follow-up through 2015. Epigenetic age acceleration (EAA) was defined as the residual of GrimAge and GrimAge2 regressed on chronological age, standardized (per 1 SD). CC was measured using standardized protocols and modeled both continuously and categorically (sex-specific cut-off: <34 cm men, <33 cm women).

Results

In midlife, GrimAge and GrimAge2 residual EAA were significantly associated with higher mortality (HR, ∼1.53 for both clocks; p<.05), whereas CC was not independently predictive. However, EAA–CC interaction terms were significant (HR, ∼0.99 for both clocks; p≈0.02). In later life, EAA was not significantly associated with mortality, while CC emerged as a significant predictor (HR per 1-cm increase, 0.94 for both clocks; p≈0.001). Stratified analyses revealed that differences in both survival probabilities and dose–response slopes between CC strata were more pronounced in midlife, whereas in later life the advantage of greater CC was attenuated, highlighting the age-dependent role of muscle reserve.

Conclusions

Epigenetic clocks robustly predicted mortality independent of chronological age, but their prognostic role was shaped by age and muscle reserve. These findings highlight the importance of integrating molecular and functional markers to improve risk stratification across the adult life course.

Key messages

• Epigenetic age acceleration predicted mortality independent of chronological age, but its prognostic role differs across the calf circumference(CC).

• In midlife, its impact was modified by CC. In later life, by contrast, CC itself emerged as the dominant predictor of survival.