Association of vitamin B12, folate, and sulfur amino acids with brain magnetic resonance imaging measures in older adults: A longitudinal population-based study by Hooshmand, B, Mangialasche, F, Kalpouzos, G, Solomon, A, Kåreholt, I, Smith, A, Refsum, H, Wang, R, Mühlmann, M, Ertl-Wagner, B, Laukka, E, Bäckman, L, Fratiglioni, L, Kivipelto, M