FIGURE 1.

Joint associations of age and red meat consumption with serum ferritin concentration in men and women. Values are multivariable-adjusted mean ferritin concentrations in women (A) and men (B) estimated from a general linear regression model. Covariates included total energy intake, annual income level, moderate-to-vigorous physical activity time, BMI (in kg/m²), alcohol intake, and serum high-sensitivity C-reactive protein concentration as continuous variables and educational status, place of residence, geographic region, and smoking status as categorical variables. To quantify a linear trend between red meat consumption and serum ferritin concentration, we assigned the median value within each quartile and modeled this variable continuously; the Wald test was used for testing statistical significance. The interaction between age group and red meat consumption was tested by adding a multiplicative term into the multivariable model for each sex group. Q, quartile.