Ask the Doctor Homocysteine

Hypothyroidism and Homocysteine

"Is there any connection between hypothyroidism and homocysteine, as in 'The Homocysteine Revolution' by K. McCulley?" -- EB, NYC

Homocysteine is an amino acid (one of the building blocks of protein) which has recently been implicated as one of the risk factors for atherosclerosis, leading to heart attacks and strokes. While physicians have not yet reached a consensus, and few recommend screening of homocysteine levels (the way we screen cholesterol), recent studies support a a 3- to 4-fold increased risk of a heart attack among patients with the highest levels of homocysteine. Folate and vitamin B12, which are involved in the metabolism of homocysteine, may help reduce levels. It is not certain whether such treatment reduces the risk of heart attacks.

Preliminary studies have found that homocysteine levels are higher in patients with untreated hypothyroidism. Homocysteine levels were not lower in patients with hyperthyroidism.

Hypothyroidism is associated with an increased risk of atherosclerosis and heart disease. There has been debate as to whether this is due to increased cholesterol levels in hypothyroid patients, or whether there is a genetic linkage between Hashimoto's thyroiditis and atherosclerosis. It now appears possible that elevated homocysteine levels are another factor.

Treatment of hypothyroidism leads to a reduction in cholesterol, LDL cholesterol, and homocysteine levels, however, so patients taking appropriate doses of levothyroxine should not have to be more concerned than the average person about their homocysteine levels.

However, pernicious anemia is an autoimmune disorder resulting in vitamin B12 deficiency. Hashimoto's thyroiditis, which is the most common cause of hypothyroidism in developed countries, is also an autoimmune disorder. Therefore, patients with Hashimoto's thyroiditis should periodically have their vitamin B12 levels assessed to prevent vitamin B12 deficiency, which would, among other things, result in higher homocysteine levels.