Table 2.

Essential criteria for showing that lowering raised tHcy can influence the outcome

Risk factor: baseline tHcy or B-vitamins*	The exposure (risk factor) to be treated, elevated tHcy or sub-optimal B vitamin status, should be present at baseline so that treatment benefit may occur
Outcome measurement	Sensitive tests must be used for measuring the outcome of the trial such as individual cognitive domains, brain volumes by MRI
Absence of dementia at baseline	Participants should not be demented, but should be at risk of cognitive decline or dementia
Duration	Should be sufficient to measure a clinically relevant change in the placebo group, e.g., cognitive decline, loss of brain volume; probably at least 12–24 months, or longer if conversion to dementia is the endpoint
Vitamin dose and combinations	Simple dietary modification is inadequate; a combination of pharmacological doses (especially of B12) of B vitamins is needed, sufficient to lower tHcy in the majority of participants
Sensitivity analysis	The protocol should pre-specify analysis according to baseline concentrations of tHcy and/or of B vitamins
Subgroup analyses	The protocol should pre-specify data analysis according to factors that may interact with the effect of B vitamin treatment, e.g., omega-3 fatty acids, other dementia risk factors and anti-platelet drug use

*In this table, the term ‘B vitamins’ means those that are directly required for homocysteine metabolism, i.e., folate, vitamin B₁₂, vitamin B₆. Vitamin B₂ may also influence homocysteine indirectly via its role as cofactor for MTHFR.