Effect modification by population dietary folate on the association between MTHFR genotype, homocysteine, and stroke risk: a meta-analysis of genetic studies and randomised trials.

By contrast with a clear effect of folate status category on the MTHFR –homocysteine association, the evidence from our subsample of studies with data for plasma folic acid concentration did not reveal a clear trend between MTHFR and plasma folic acid across probable folate categories (data not shown). 140 datasets from 101 studies including 20 885 stroke events met our selection criteria and were included in the meta-analysis of MTHFR 677C→T polymorphism and stroke ( webappendix pp 20–21 ). 94 datasets measured ischaemic stroke (17 909 cases), 20 haemorrhagic stroke (1615 cases), one silent brain infarction (161 cases), and 25 total stroke (6972 cases, including ischaemic and haemorrhagic cases, resulting in overlap between categories).

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