Increased Levels of Homocysteine

Hyperhomocysteinemia, or increased levels of the amino acid, homocysteine, affects about 5% of the general population. Approximately 13-47% of people with symptoms of heart disease have this condition. Mild to moderately high levels of homocysteine is a single risk factor for stroke, heart attack, peripheral arterial disease, and narrowing of the extracranial carotid artery.

High levels of homocysteine are also associated with enzyme defects or decreased amounts of folate or vitamin B6, particularly in the elderly. Mild or moderate hyperhomocysteinemia has been associated with venous blood clots in the young and recurrent blood clots. The condition also has been found in approximately 10% of patients who experience their first episode of a venous blood clot.

Several inherited or acquired conditions may lead to an increase in homocysteine levels.


Inherited causes of hyperhomocysteinemia include low levels of an enzyme needed to change homocysteine into cysteine. In turn, this increases the risk of a clotting event. Mild inherited hyperhomocysteinemia has been found in 19% of cases of venous clotting in children.


Acquired causes of hyperhomocysteinemia include:

  • Advanced age

  • Tobacco use

  • Coffee intake

  • Low levels of folate in the diet

  • Low intake of vitamin B

Increased homocysteine levels are also associated with diabetes mellitus, cancers, low level of thyroid function, lupus, and inflammatory bowel disease; and are a side-effect of certain medications such as cholesterol-lowering agents, metformin, methotrexate, anticonvulsants, theophylline, and levodopa.