In a sample of 1,092 men and women without dementia followed for an average of 10 years, those with higher plasma homocysteine levels at baseline had a significantly higher risk of developing Alzheimer's disease and other types of dementia. (lpi.oregonstate.edu)
However, when methionine - rich diets are used to induce hyperhomocysteinemia... Mice fed methionine - rich diets had significant atheromatous pathology in the aortic arch even with normal plasma homocysteine levels, whereas mice fed B vitamin - deficient diets developed severe hyperhomocysteinemia without any increase in vascular pathology. (nutritionfacts.org)
Several factors influence plasma homocysteine levels, such as intake of folic acid and vitamin B12, age, gender, heredity, smoking, hypertension, and physical activity39. (coffeeandhealth.org)