Introduction

Risk factors for Alzheimer’s disease (AD) affecting the rate of cognitive decline and brain shrinkage include nonmodifiable factors such as age, low education levels, and genetic factors, whereas modifiable risk factors have also been identified. One such modifiable risk factor is homocysteine (Hcy), an amino acid that is produced in the methylation cycle of protein metabolism. The association between elevated plasma Hcy and cognitive impairment has been well established (Budge et al., 2002, McCaddon et al., 2001 and Seshadri, 2006), although the underlying mechanisms to explain the association are still being researched.

The Hcy pathway

Hcy is produced via protein metabolism. The conversion of Hcy to useful metabolites, S-adenosyl methionine and glutathione, requires vitamins B9 (methyl folate), B12 (cobalamin), and B6 (pyridoxine) as cofactors ( Morris, 2012a and Refsum et al., 2006). Hence, if the B-vitamin supply through the diet is suboptimal, remethylation of Hcy via the enzyme methionine…