Identification of modifiable risk factors provides a crucial approach to the prevention of dementia. Nutritional or nutrient-dependent risk factors are especially important because dietary modifications or use of dietary supplements may lower the risk factor level. One such risk factor is a raised concentration of the biomarker plasma total homocysteine, which reflects the functional status of three B vitamins (folate, vitamins B12, B6). A group of experts reviewed literature evidence from the last 20 years. We here present a Consensus Statement, based on the Bradford Hill criteria, and conclude that elevated plasma total homocysteine is a modifiable risk factor for development of cognitive decline, dementia, and Alzheimer’s disease in older persons. In a variety of clinical studies, the relative risk of dementia in elderly people for moderately raised homocysteine (within the normal range) ranges from 1.15 to 2.5, and the Population Attributable risk ranges from 4.3 to 31%. Intervention trials in elderly with cognitive impairment show that homocysteine-lowering treatment with B vitamins markedly slows the rate of whole and regional brain atrophy and also slows cognitive decline. The findings are consistent with moderately raised plasma total homocysteine (>11 μmol/L), which is common in the elderly, being one of the causes of age-related cognitive decline and dementia. Thus, the public health significance of raised tHcy in the elderly should not be underestimated, since it is easy, inexpensive, and safe to treat with B vitamins. Further trials are needed to see whether B vitamin treatment will slow, or prevent, conversion to dementia in people at risk of cognitive decline or dementia.

The evidence derived from these limited studies suggests that 2000 mcg doses of oral vitamin B12 daily and 1000 mcg doses initially daily and thereafter weekly and then monthly may be as effective as intramuscular administration in obtaining short term haematological and neurological responses in vitamin B12 deficient patients.

Serum homocysteine is increased, and correlates inversely with cognitive scores, in Alzheimer’s disease (AD), vascular dementia and ‘age-associated memory impairment’. Elevated levels might signal accelerated cognitive decline, although this remains to be established. We therefore repeated Mini-Mental State Examinations, together with additional ADAS-Cog assessments, in 32 healthy elderly individuals to determine whether prior homocysteine levels predicted cognitive changes over a 5-year period. Homocysteine predicted follow-up cognitive scores and rate of decline in cognitive performance independently of age, sex, education, renal function, vitamin B status, smoking and hypertension (p < 0.001). Homocysteine predicted word recall (p = 0.01), orientation (p = 0.02) and constructional praxis scores (p < 0.0001). One subject, with the second highest initial homocysteine, had developed probable AD at follow-up. Fasting total serum homocysteine appears to be an independent predictor of cognitive decline in healthy elderly and exerts a maximal effect on spatial copying skills.

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