Fig. 2

Exposure-response association of dietary live microbe intake with the prevalence of frailty among older adults in NHANES 1999–2018 using restricted cubic spline (RCS) regression. The red line represents the odds ratios (ORs) for frailty prevalence across the range of dietary live microbe intake, with the shaded blue area indicating the corresponding 95% confidence intervals (CIs). A significant P-value for nonlinearity (< 0.001) suggests that the association is nonlinear. The inflection point at 161.82 (dashed vertical line) represents a threshold where the slope of the relationship changes. The results indicate that higher dietary live microbe intake is associated with lower odds of frailty, particularly below the inflection point. Analyses were adjusted for age (continous), sex (male or female), race/ethnicity (Non-Hispanic White, Non-Hispanic Black or Other), marital status (married/living with partner, or single/divorced/widowed), education level (below high school, high school, or above high school), family PIR (≤ 1.0, 1.1–3.0, or > 3.0), drinking status (nondrinker, former drinker, or current drinker), smoking status (never smoker, former smoker, or current smoker), and HEI (in quartiles)