P3‐408: THE GUT MICROBIOTA‐DERIVED METABOLITE TRIMETHYLAMINE N‐OXIDE (TMAO) IS ASSOCIATED WITH REDUCED NEUROIMAGING MEASURES OF CEREBROVASCULAR HEALTH IN COGNITIVELY UNIMPAIRED LATE MIDDLE‐AGED ADULTS. (1st July 2019) - Vogt, Nicholas M.; Hunt, Jack F.V.; Cary, Paul; Engelman, Corinne D.; Carlsson, Cynthia; Asthana, Sanjay; Johnson, Sterling C.; Rivera-Rivera, Leonardo A.; Wieben, Oliver; Rey, Federico E.; Bendlin, Barbara B.