RecruitingEarly Phase 1Dietary supplementType 2 Diabetes and Blood Brain Barrier ImprovementThe majority of T2DM adults show thiamine (vitamin B1) deficiency which may contribute to impaired function. This study will examine patients with T2DM through brain MRI scans, cognition assessments, blood tests, and questionnaires. Our goal is to see if a thiamine treatment (taking vitamin B1 capsules) can improve function. Patients will be asked to come to UCLA two times three months apart and each visit will last about 2.5-3 hours.