Homocysteine (Hcy) is a risk factor for brain
atrophy,
cognitive impairment, and
dementia.
Vitamin B12 and
folate are cofactors necessary for the methylation of Hcy. However, there is some debate regarding the differing levels of plasma Hcy and serum
folate and
vitamin B12 among healthy controls, patients with
mild cognitive impairment (MCI), and patients with
Alzheimer's disease (AD). This study aimed to evaluate how the levels of plasma Hcy and its
biological determinants,
folate and
vitamin B12, are related to MCI and AD in older Chinese adults. This is a case-control study including 112 subjects with MCI, 89 AD patients and 115 healthy controls. Diagnosis of AD was made according to the NINCDS-ADRDA and MCI with modified Petersen's criteria. Serum
folate and
vitamin B12 concentrations were analyzed by radioimmunoassay, and plasma Hcy was assessed by a high-performance liquid chromatography-fluorescence method. Multivariate analysis of regression was used to examine the odds ratio (OR) of MCI or AD with Hcy or
vitamin levels. Results have shown that serum
folate and
vitamin B12 levels were significantly lower, but the plasma Hcy level was higher, in patients with MCI and AD than in healthy controls. Multivariate regression analyses showed that subjects in the lowest
folate tertile had significantly higher adjusted
ORs for MCI (OR: 3.07; 95% confidence interval [CI]: 1.12, 8.07) and AD (3.42; 95% CI: 1.15, 8.34) compared to subjects in the highest tertile. The highest Hcy tertile was significantly associated with MCI (adjusted OR: 2.81; 95% CI: 1.15, 4.73) and AD (adjusted OR: 3.64; 95% CI: 1.13, 9.04) compared to the lowest tertile. No association existed between low
vitamin B12 levels and AD or MCI (p > 0.05). Low blood levels of
folate and
vitamin B12 and elevated Hcy levels were associated with MCI and AD in older Chinese adults, and the association was stronger for AD.