Changes in Vitamin B12, Homocysteine, and Neurological Function in Older Adults

Vitamin B12 deficiency affects 5-20% of older adults, with up to 40% with low B12 levels [<260pmol/L]. The risk of B12 deficiency increases with age. Vitamin B12 is essential for neurological function, and B12 deficiency is a known cause of clinical neuropathy and has been associated with cognitive impairment. However, little is known about the relationship between low B12 levels and peripheral nerve function and information processing speed, cross-sectionally or longitudinally, in older adults. The purpose of this dissertation is to examine whether low B12 levels or change in B12 levels were associated with peripheral nerve function or information processing speed. We examined whether low B12 or high homocysteine [≥13µmol/L] and 3-year change in B12 and homocysteine was associated with 6-year change in peripheral nerve function or neurological signs in older Italian adults from the InCHIANTI Study. We found high homocysteine was associated with lower nerve conduction amplitude and greater inability to detect 4g monofilament. In the Health ABC Study, we studied whether low [<260pmol/L] or deficient [<260pmol/L & methylmalonic acid [MMA] >271nmol/L & MMA>2-methylcitrate] B12 were associated with peripheral sensory and motor nerve function, and evaluated whether there was a threshold effect of serum B12 levels on peripheral nerve function in older black and white adults. We found poor B12 were associated with greater insensitivity to 1.4g monofilament and worse nerve conduction velocity [NCV] and there was a significant serum B12 threshold level of 390 pmol/L for NCV. To consider cognitive function, we examined whether low B12 or 7-year change in B12 were associated with decline in Digit Symbol Substitution Test [DSST] scores over 6-years. We found low B12 was associated with greater DSST decline and a serum B12 level of 410 pmol/L was associated with lower DSST decline. These results have important public health significance, because low B12 levels, above clinical deficiency [