A study published in Canadian Medical Association Journal found that people low in vitamin B12 had an increased risk of deadly heart attacks and stroke. Researchers studied 421 middle-age people. The degree of occlusion from plaque in the carotid arteries was measured using ultrasound. Blood levels of vitamin B12 and homocysteine were measured as well. The amount of plaque was significantly higher in those who had a deficiency of vitamin B12. Low vitamin B12 is a major cause of elevated homocysteine levels.
Comments: Serum (blood) levels of vitamin B12 do not always reflect cellular levels. Better markers of vitamin B12 status are homocysteine and methylmalonic acid. Both are routinely available at most labs.