HIGH SERUM-CHOLESTEROL LEVELS IN PERSONS WITH HIGH-NORMAL TSH LEVELS - SHOULD ONE EXTEND THE DEFINITION OF SUBCLINICAL HYPOTHYROIDISM

Objective: The association between established hypothyroidism and high cholesterol levels is well known. The aim of the present study was to investigate the effect of thyroxine (T-4) administration on cholester ol levels in hypercholesterolemic subjects with TSH levels within the normal range ('high-normal' TSH compared with 'low-normal' TSH). Desig n and Methods: We determined TSH levels in 110 consecutive patients re ferred for hypercholesterolemia (serum cholesterol > 7.5 mmol/l). Thos e with 'high-normal' TSH (2.0-4.0 mu U/ml) as well as those with 'low- normal' TSH (0.40-1.99 mu U/ml) were randomly assigned to receive eith er 25 or 50 mu g T-4 daily for two months. Thus, groups A and B (low-n ormal TSH) received 25 and 50 mu g T-4 respectively and groups C and D (high-normal TSH) received 25 and 50 mu g T-4 respectively. Serum T-4 , tri-iodothyronine (T-3), TSH, free thyroxine index, resin T-3 uptake and thyroid autoantibodies (ThAab) as well as total cholesterol, high and low density lipoprotein cholesterol (HDL. LDL), and triglycerides were determined before and at the end of the two-month treatment peri od. Results: TSH levels were reduced in all groups, The most striking effect was observed in group D (TSH levels before: 2.77 +/- 0.55, afte r: 1.41 +/- 0.85 mu U/ml, P < 0.01). Subjects in groups C and D had a higher probability of having positive ThAabs. A significant reduction in total cholesterol (P < 0.01) and LDL (P < 0.01) was observed after treatment only in group D. In those subjects in group D who were ThAab negative, there was no significant effect of thyroxine on cholesterol levels. Conclusions: Subjects with high-normal TSH levels combined wi th ThAabs may, in fact, have subclinical hypothyroidism presenting wit h elevated cholesterol levels. It is possible that these patients migh t benefit from thyroxine administration.