Randomised controlled trials (RCTs) of adults (>19 years of age) that measured vascular reactivity using percentage of flow-mediated dilatation after folic acid supplementation without a vascular challenge (such as methionine or fat load) were eligible for inclusion. The primary outcome of interest was net change in flow-mediated dilatation.
Median duration of treatment with folic acid was eight weeks (range four to 52 weeks); median dose was 5000ug/day (range 400ug/day to 10,000ug/day). Median age of participants was 55.8 years (mean age range 29.3 to 69.1 years). In most trials most people were male (median 86%). Patient populations were either healthy, healthy but with elevated plasma homocysteine levels, or with cardiovascular disease (or high cholesterol). Some studies supplied additional vitamin B-6 and vitamin B-12. It appeared that all comparator groups received placebo.
Two reviewers independently selected studies for inclusion.