Lipoprotein(a) and other lipoproteins in hypothyroid patients before and after thyroid replacement therapy.
OBJECTIVE
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 control euthyroid subjects were evaluated in a cross- sectional study, determining thyroid function tests and fasting serum lipids and lipoproteins. In a follow-up study for those hypothyroid patients the same determinations were repeated after normalization of thyroid state by levothyroxine (L-T(4)) replacement therapy. Patients needing other treatments were excluded. At baseline, patients with hypothyroidism had significantly higher levels of Lp(a), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), apolipoprotein (apo) A-I and apo B, and a higher TC/high-density lipoprotein cholesterol (HDL-C) ratio than control subjects.


RESULTS
Severity of the hypothyroid state, expressed by serum thyroid-stimulating 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 pretreatment Lp(a) levels were also correlated with those of posttreatment Lp(a)(r= 0.68, P= 0.002). All patients, who presented basal Lp(a) levels higher than 30 mg/dl, showed a decrease in Lp(a) concentrations by L-T(4)therapy, 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, CAD 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) concentrations. Lp(a) levels may be at least partially modulated by thyroid hormone-dependent mechanisms, thus increasing the risk of developing premature atherosclerosis in hypothyroid state, that might be reduced by L-T(4)therapy.
Becerra
A
A
Department of Endocrinology, Hospital Ramón y Cajal, Madrid, Spain.
Bellido
D
D
Luengo
A
A
Piédrola
G
G
De Luis
D A
DA
D000328:Adult; D000368:Aged; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000097:blood* / Q000145:classification / Q000188:drug therapy*; D017270:Lipoprotein(a) / Q000097:blood*; D008074:Lipoproteins / Q000097:blood*; D008297:Male; D008875:Middle Aged; D012720:Severity of Illness Index; D013960:Thyroid Function Tests; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000627:therapeutic use*
D017270:Lipoprotein(a); D008074:Lipoproteins; D013972:Thyrotropin; D013974:Thyroxine