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Plasma Total Homocysteine Levels during Short-Term Iatrogenic Hypothyroidism¹

Division of Pharmacology (E.A.L., P.M.U.), Division of Endocrinology, Department of Internal Medicine (B.G.N.), Division of Endocrine Surgery, Department of Surgery (J.E.V.), Section for Medical Informatics and Statistics (O.N.), Department of Biochemical Endocrinology (A.A.), University Hospital of Bergen, N-5021 Bergen, Norway

Address all correspondence and requests for reprints to: Dr. Ernst A. Lien, Department of Biochemical Endocrinology, University Hospital of Bergen, N-5021 Bergen, Norway. E-mail: ernst.lien{at}ikb.uib.no

Hypothyroidism is associated with increased cardiovascular morbidity, which cannot be fully explained by the atherogenic lipid profile observed in these patients. We have previously found elevated levels of the cardiovascular risk factor, plasma total homocysteine (tHcy), in hypothyroidism.

We conducted a longitudinal study on 17 patients who had undergone total thyroidectomy for thyroid cancer. During 6 weeks of discontinued T₄ substitution before radioscintigraphy (phase I), they attained a hypothyroid state, which was reversed by resupplementation (phase II). Plasma tHcy, serum creatinine, serum and red blood cell folate, serum cobalamin, and serum cholesterol were determined at 2-week intervals throughout phases I and II.

There was a progressive and parallel increase in tHcy (mean, 27%), serum creatinine (37%), and serum cholesterol (100%) during phase I, and these values returned to the original level within 4–6 weeks after reinitiating T₄ therapy. Serum and red blood cell folate levels showed only minor, but statistically significant, changes. In a bivariate model, serum creatinine and serum cholesterol were strongly associated with the changes observed in tHcy during short term hypothyroidism.

In conclusion, we found a transient increase in both plasma tHcy and serum cholesterol during short term iatrogenic hypothyroidism, and the tHcy response is probably mainly explained by concurrent changes in renal function. The increase in both plasma tHcy and serum cholesterol may confer increased cardiovascular risk in hypothyroid patients.

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