 Covariates Covariates included age, sex, race White vs. African American, marital status, educational attainment HS, poverty income ratio PIR125 for poor, measured body mass index BMI, kgm2, opiate, marijuana or cocaine use current vs. never or former, smoking status current vs. never or former and the Wide Range Achievement Test WRAT letter and word reading subtotal scores to measure literacy. See Supplemental Method 1 To assess depressive symptoms with focus on affective, depressed mood, the 20-item CES-D was used. Baseline CES-D total score was included in the analysis as a potential confounder in the association between vitamin D exposures and cognitive change or baseline performance. See Supplemental Method 1 The Healthy Eating Index HEI-2010 total score, based on two 24-hr recalls administered at baseline, was used as a measure of overall dietary quality. See steps for calculating HEI-2010 at and Further, season of baseline MRV exam was used as proxy for sunshine exposure and was included as covariate in all models. Finally, self-reported history of type 2 diabetes, hypertension, cardiovascular disease stroke, congestive heart failure, non-fatal myocardial infarction or atrial fibrillation and dyslipidemia at first-visit were considered as covariates.40 Statistical analysis Using Stata 15.0 41 and accounting for sampling weights, population estimates of means and proportions were obtained. Means across stratifying variables e.g. agesex or race were compared using svy:reg, relationship between categorical variables using svy:tab and design-based F-tests. Further, mixed-effects regression models with 11 continuous cognitive test scores as alternative outcomes were conducted. In these models the time variable was interacted with several covariates including the main exposure variables, namely VITDserum, VITDdiet and VITDsuppl. The models assume missingness at random with time points ranging between 1.5-2.0 visitsperson. 42 Predictive margins were estimated and plotted across TIME, stratifying by exposure group, from selected mixed-effects regression models, particularly those showing significant associations in the total population. 