Risk mechanisms
How low vitamin B12 may connect with cardiovascular disease risk
The proposed link between low B12 and cardiovascular risk runs through metabolism, blood cells and the factors that cause B12 levels to fall.
Homocysteine and methylation
B12 is required for methionine synthase, which helps convert homocysteine back to methionine. Deficiency can disrupt this cycle and raise homocysteine, although the clinical meaning depends on the whole patient picture.
Anemia and oxygen delivery
Severe B12 deficiency can cause megaloblastic anemia. Anemia changes how oxygen is delivered and can add stress for people who already have cardiovascular disease, but this is different from proving that low B12 independently causes atherosclerosis.
Shared risk factors
Older age, malabsorption, metformin, acid-reducing medicines, restrictive diets and kidney disease can overlap with cardiovascular disease risk. This is one reason the low B12 cardiovascular risk review needs careful adjustment for confounding.