BackgroundCancer remains a serious public health problem impeding gains in life expectancy. Epigenetic clocks, derived from sets of DNA methylation CpGs and mathematical algorithms, have demonstrated a remarkable ability to indicate biological aging and age-related health risks. Dunedin(P)ace(o)f(A)ging(m)ethylation is a single-timepoint DNA methylation clock. It is an aging speedometer rather than a state measure. The association between the DunedinPoAm-measured pace of biological aging and cancer risk based on a nationally non-institutionalized sample remains to be elucidated. Physical activity, a modifiable lifestyle factor, is associated with delayed biological aging and lower risks of developing cancer. We hypothesized that DunedinPoAm-measured pace of biological aging is positively associated with cancer risk, and physical activity moderates this association. ResultsIn total, 2,529 participants aged 50 or older from the National Health and Nutrition Examination Survey (NHANES) 1999-2002 were included. Weighted logistic regression calculating odds ratios (OR) and 95% confidence intervals (CI) showed that when scaled per 1-SD increase, DunedinPoAm was positively associated with cancer risk (OR, 95% CI) (1.21, 1.05-1.39) in the crude model and adjusted for age and sex (1.19, 1.01-1.40). Individuals of high DunedinPoAm tertile had a 68% (95% CI 1.16-2.43) increase in cancer risk compared with the low tertile (P trend < 0.001). As hypothesized, effect modification by physical activity was significant (P interaction = 0.013). The association was apparent in physically inactive participants (1.52, 1.16-2.00), whereas insignificant in physically active individuals (1.08, 0.89-1.32). Exploratory interaction analyses for other covariates showed significant effect modification by age (> 65 years, 1.38, 1.08-1.77 vs 50-65 years, 1.00, 0.79-1.27). ConclusionThe study supported the hypothesis by demonstrating a positive association between the DunedinPoAm-measured pace of biological aging and cancer risk and a modulating role of physical activity. Physically inactive individuals or participants over 65 years showed increased susceptibility to this association. These findings suggest that incorporating the DunedinPoAm-measured pace of biological aging into cancer screening strategies may benefit those with physically inactive lifestyles and older individuals. Whether physical activity can mitigate the increased risk of cancer in individuals with a faster pace of biological aging needs to be validated in further interventional cohort studies.