The BMI and smoking associations with T2* are found in distinct subcortical structures. Interestingly, this distinction is reflected in the CCA-ICA results, where these associations appear in separate population modes. The association of T2* in caudate and putamen with smoking (and more weakly with alcohol, Fig 8c) is highly concordant with CCA-ICA mode 5 (Supplementary Fig 4b), and is associated with aging (Fig 8c and Supplementary Fig 8). The association of T2* in hippocampus and amygdala with BMI is highly concordant with CCA-ICA mode 3 (Supplementary Fig 3c), a distinct mode of population covariation that is not associated with aging (in either analysis). Neither mode includes cognitive test scores, suggesting that while these associations clearly relate to biological processes, they may be only indirectly linked to cognitive health.
