Homocysteine and Cardiovascular Disease

Elevated homocysteine is associated with a 2- to 3-fold increased risk of atherosclerotic vascular disease, particularly stroke, though treatment with B vitamins to lower homocysteine has shown inconsistent cardiovascular benefits in clinical trials 1

Cardiovascular Risk Factors

For every 5 μmol/L increase in homocysteine, stroke risk increases by 59% (95% CI, 29-96%) 1
Conversely, for every 3 μmol/L decrease in homocysteine, stroke risk decreases by 24% (95% CI, 15-33%) 1
Meta-analyses show a 19% reduction in stroke odds per 25% lower homocysteine concentration after adjusting for smoking, blood pressure, and cholesterol 1
An increment of 5 mmol/L in total homocysteine is equivalent to the CAD risk induced by a 20 mg/dL increase in plasma cholesterol 2, 3
Homocysteine accounts for up to 10% of the population's CAD risk 2, 3
Lowering homocysteine by 3 mmol/L would theoretically reduce ischemic heart disease risk by 16% 2
Elevated homocysteine is associated with increased carotid intima-media thickness and carotid artery stenosis 1

Deficiency in cystathionine β-synthase (transsulfuration pathway enzyme) causes hyperhomocysteinemia 1, 4
Deficiency in methylenetetrahydrofolate reductase (MTHFR) in the remethylation pathway causes elevated levels 1, 4
Pyridoxine (vitamin B6) deficiency—a cofactor for cystathionine β-synthase 1, 4
Folic acid deficiency—a cofactor for MTHFR 1, 4
Cobalamin (vitamin B12) deficiency—a cofactor for MTHFR 1, 4
Decreased renal clearance in chronic kidney disease leads to hyperhomocysteinemia 1, 4

The American Heart Association/American Stroke Association states that B complex vitamins (cobalamin/B12, pyridoxine/B6, and folic acid) might be considered for prevention of ischemic stroke in patients with hyperhomocysteinemia, but its effectiveness is not well established (Class IIb; Level of Evidence B) 5
The HOPE-2 study showed a 25% stroke reduction (RR 0.75; 95% CI, 0.59-0.97) with combination B6, B12, and folic acid therapy, though the composite endpoint was not reduced 5
Meta-analysis of folic acid supplementation showed a trend toward reduced stroke risk (RR 0.93; 95% CI, 0.86-1.00) 5
Stroke reduction was stronger (RR 0.89; 95% CI, 0.79-0.99) in participants without prior stroke 5
Folic acid 0.4-1 mg daily reduces homocysteine by approximately 25-30% 4
Adding vitamin B12 (0.02-1 mg/day) provides an additional 7% reduction 4