FIGURE 4.

A data-driven iron status composite index is associated with age, sex, SES, and cognitive performance. (A) We generated a composite iron status index and a composite inflammatory index using PCA. The PCA (n = 690) separated patterns of covariation in Hgb, ferritin, and transferrin attributable to iron status effects from inflammatory effects. Greater values of the iron status index indicate greater Hgb, greater ferritin, and lower transferrin. Conversely, lower values indicate lower Hgb, lower ferritin, and higher transferrin (as would be expected in the case of iron deficiency). In contrast, lower scores on the inflammatory index reflect greater ferritin, lower Hgb, and higher transferrin (as would be expected in inflammation). These indices were highly similar to a confirmatory model that included a subset of 137 individuals for whom the inflammatory marker CRP was also available (r = 0.91; Supplemental Figure 4). The composite iron status index was significantly associated with age and sex [n = 690; panel (B)], neighborhood SES [n = 690; panel (C)], and overall accuracy on a battery of cognitive tests [n = 31; R²_partial = 0.31; panel (D)]. Individual points represent observations with lines connecting repeated observations from the same individual; data across time are collapsed for each individual in panel C. Thick lines reflect model fits and shaded areas reflect 95% CIs of the fit (B–D). Hgb, hemoglobin; PC, principal component; PCA, principal component analysis; SES, socioeconomic status.