body.
The issue is often high-dose synthetic folic acid, which is found in many multivitamins, B-complex products, and standalone folic acid tablets. Folic acid is vitamin B9, and it is often combined with vitamin B6 and vitamin B12.
These vitamins are connected to homocysteine, an amino acid in the blood. High homocysteine has been linked with cardiovascular and stroke risk, so researchers studied whether lowering homocysteine with B vitamins could prevent strokes. Some studies suggest possible benefit in certain groups, but the evidence is not simple or universal. A Cochrane
