We also performed subgroup meta - analyses by
type of prevention (primary v secondary: in this study, trials involving healthy populations or patients with any specific disease except for cardiovascular disease were classified as primary prevention trials, and trials involving patients with cardiovascular disease were classified as secondary prevention trials),
type of supplement by quality and dose (each supplement, vitamins only, antioxidants only, or antioxidants excluding vitamins),
type of outcome (cardiovascular death, angina,
fatal or non-
fatal myocardial infarction,
stroke, or transient ischaemic attack),
type of outcome in each supplement,
type of study design (randomised, double blind, placebo controlled trial v open label, randomised controlled trial), methodological quality (high v low), duration
of treatment (< 5 years v ≥ 5 years), funding source (pharmaceutical industry v independent organisation), provider
of supplements (pharmaceutical industry v not pharmaceutical industry),
type of control (placebo v no placebo), number
of participants (≥ 10000 v < 10000), and supplements given singly or in combination with other vitamin or antioxidant supplements by quality.