Lipoprotein(a) and other lipoproteins in hypothyroid patients before and after thyroid replacement therapy

Aims: To analyse the influence of thyroid hormones on serum lipoprotein(a) (Lp(a)) concentration and other lipid parameters, and hence potentially on coronary artery disease (CAD) risk. Methods: Thirty-six patients with hypothyroidism and 165 age-matched contro l euthyroid subjects were evaluated in a cross- sectional study, determinin g thyroid function tests and fasting serum lipids and lipoproteins. In a fo llow-up study for those hypothyroid patients the same determinations were r epeated after normalization of thyroid state by levothyroxine (L-T-4) repla cement therapy. Patients needing other treatments were excluded. At baselin e, patients with hypothyroidism had significantly higher levels of Lp(a), t otal cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), apolipo protein (apo) A-I and apo B, and a higher TC/high-density lipoprotein chole sterol (HDL-C) ratio than control subjects. Results: Severity of the hypothyroid state, expressed by serum thyroid-stim ulating hormone, was correlated with serum levels of Lp(a), LDL-C, and TC ( r = 0.64, 0.52, 0.49, P = 0.005, P = 0.033, P = 0.048, respectively). The p retreatment Lp(a) levels were also correlated with those of posttreatment L p(a)(r = 0.68, P = 0.002). All patients, who presented basal Lp(a) levels h igher than 30 mg/dl, showed a decrease in Lp(a) concentrations by L-T, ther apy, and these normalized in eight cases (22.2%). Euthyroid state gave rise to a significant reduction of serum Lp(a) by 32.3%, of LDL-C by 22.8%, of TC by 17%, of apo A-I by 9.6%, and of apo B by 9.3%. After L-T-4 therapy, C AD risk, expressed as TC/HDL-C ratio, decreased by 19.9%. Conclusions: These results show that hypothyroidism is associated not only with elevated serum levels of LDL-C but also with elevated serum Lp(a) conc entrations. Lp(a) levels may be at least partially modulated by thyroid hor mone-dependent mechanisms, thus increasing the risk of developing premature atherosclerosis in hypothyroid state, that might be reduced by L-T-4 thera py. (C) 1999 Harcourt Publishers Ltd.