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 cholesterol
levels in hypercholesterolemic subjects with TSH levels within the
normal range (’high-normal’ TSH compared with ‘low-normal’ TSH).
Design and Methods: We determined TSH levels in 110 consecutive patients
referred for hypercholesterolemia (serum cholesterol > 7.5 mmol/l).
Those 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
either 25 or 50 mu g T-4 daily for two months. Thus, groups A and B
(low-normal 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 period.
Results: TSH levels were reduced in all groups, The most striking effect
was observed in group D (TSH levels before: 2.77 +/- 0.55, after: 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 with ThAabs
may, in fact, have subclinical hypothyroidism presenting with elevated
cholesterol levels. It is possible that these patients might benefit
from thyroxine administration
