Homocysteine, folate, and vitamin B-12 in mild cognitive impairment, Alzheimer disease, and vascular dementia.

BACKGROUND Evidence supports an independent association between plasma total homocysteine concentrations and the risk of vascular disease. Recent epidemiologic studies reappraised the possibility that vascular risk factors might play a role in the pathogenesis not only of vascular dementia (VaD) but also of Alzheimer disease (AD). OBJECTIVE The objective was to investigate the relations of mild cognitive impairment, AD, and VaD with blood homocysteine, folate, and vitamin B-12. DESIGN The study population consisted of 314 consecutive subjects, 228 of whom were eligible for analyses. Plasma total homocysteine, serum folate, and serum vitamin B-12 concentrations were measured in 55 nondemented elderly control subjects, 81 mildly cognitively impaired subjects (Clinical Dementia Rating: 0.5), and 92 demented patients prevalently in a mild disease stage and with a clinical diagnosis of AD (n = 74) or VaD (n = 18). RESULTS Subjects in the lowest folate tertile had significantly higher adjusted odds ratios (ORs) for mild cognitive impairment (OR: 3.1; 95% CI: 1.2, 8.1) and dementia (3.8; 1.3, 11.2). Hyperhomocysteinemia was significantly associated with dementia (adjusted OR: 4.3; 1.3, 14.7) and AD (adjusted OR: 3.7; 1.1, 13.1). In subjects with a Clinical Dementia Rating of 0.5, the mean (+/- SE) Mini-Mental State Examination score was significantly lower (P < 0.05) in the highest homocysteine tertile (24.5 +/- 0.5) than in the lowest tertile (26.6 +/- 0.5). No significant associations were found between minimum medial temporal lobe thickness or leukoaraiosis and any biochemical measure in the dementia and AD groups. CONCLUSIONS These findings suggest that relative folate deficiency may precede AD and VaD onset. Hyperhomocysteinemia might also be an early risk factor for cognitive decline in the elderly, but its role in dementia development must be addressed in future longitudinal studies.