Homocysteine is a toxic amino acid, a breakdown product of protein metabolism that has been linked to heart attacks and strokes. At elevated levels, homocysteine is thought to contribute to plaque formation by damaging arterial walls. High homocysteine levels may also act on blood platelets and increase the risks of clot formation. In addition, some evidence suggests that people with high homocysteine levels have twice the normal risk of developing Alzheimer's disease.
Blood levels of homocysteine tend to be highest in people who eat a lot of animal protein. These people also tend to consume few fruits and leafy vegetables, which provide the folic acid and other B vitamins that help the body get rid of homocysteine.
In addition to its derivation from dietary protein, homocysteine is also produced in the body from another amino acid, methionine. One of methionine's main functions is to provide methyl groups for cellular reactions. A methyl group is a chemical fragment consisting of one carbon and three hydrogen atoms. When methionine donates a methyl group for a cellular reaction, it becomes homocysteine. Typically, homocysteine then receives another methyl group from either folic acid or vitamin B6 to regenerate methionine. Vitamin B12 acts as a co-factor for this reaction.
An inadequate intake of B vitamins, as well as genetic factors that affect the body's absorption and use of folic acid, can lead to high homocysteine levels. If this is the case, you need much more folic acid than the RDA of 400 mcg.
Other contributors to elevated homocysteine levels include stress and coffee consumption. The more coffee you drink, the higher your homocysteine levels are likely to be. The stress-induced neurotransmitters epinephrine and norepinephrine are metabolized in the liver via a process that uses methyl groups. This can also increase the need for folic acid.
To lower homocysteine levels, I recommend increasing your intake of B vitamins and moderating stress. The richest food sources of folate (the form of folic acid found in food) are green vegetables, orange juice and beans. I also recommend taking a multivitamin that gives you 400 micrograms of folic acid in addition to what you might get from your diet (Some people might absorb this vitamin better in supplement form, and I consider this good insurance.) To reduce stress, practice breathing exercises, meditation and mind-body exercises such as yoga.
Reducing foods high in animal protein can also help lower homocysteine levels, but I don't think you need to worry about restricting your intake of methionine. For optimum health, I recommend following my anti-inflammatory diet, which limits total protein intake to between 80 and 120 grams (three to four ounces) daily from fish, beans, whole soy and dairy products.
Andrew Weil, M.D.