Prevalence of subclinical hypothyroidism in hypercholesterolemic adults and influence of serum TSH on the serum total cholesterol level

Jeong, Won Jea; Kim, Young Seol; Park, Byeong Heon; Park, Cheol Young; Ryu, Mee Sook; Oh, Seung Joon; Woo, Jeong Tack; Kim, Sung Woon; Yang, In Myoung; Kim, Jin Woo; Choi, Young Kil; Paeng, Jeong Ryung

Abstract

BACKGROUND
Subclinical hypothyroidism is frequently discovered from hypercholesterolemic adults. It is defined as an asymptomatic state which characterized by normal free thyroxine (FT4) and elevated thyroid stimulating hormone (TSH) level. Hypercholesterolemia is a major risk factor for coronary heart disease, however hypercholesterolemia caused by hypothyroidism can be easily managed by thyroid hormone replacement. The screening of thyroid disease in hypercholesterolemia patient must be emphasized in order to find out correctable hypothyroidism. So we screened the prevalence of overt and subclinical hypothyroidism at different hypercholesterol levels in middle-aged men and women and also analyzed the correlation between TSH and total cholesterol level.
METHODS
We measured serum TSH levels and FT4 by radioimmunoassay from 491 patients with hypercholesterolemia. The subjects were divided into two groups according to serum cholesterol level. Group I was serum cholesterol > or = 240 -<300 mg/dL and group II was > or = 300 mg/dL. Subclinical hypothyroidism was defined as TSH levels higher than 4 mU/L, in the presence of normal FT4 concentration.
RESULTS
The overall prevalence of subclinical and overt hypothyroidism was 3.4% and 2.5% in men and 4.7% and 3.5% in women of middle age. In men the prevalence of overt and subclinical hypothyroidism increased from 2.3% of group I to 16.1% in the group II (p<0.05). In women that increased from 5.2 % to 12.9 % (p<0.05). After age correction, an increase of 1 mU/L TSH in men was associated with an increase of 3.2 mg/dL total cholesterol (p<0.01). A similar trend was also found in women (2.1 mg/dL p=0.052).
CONCLUSION
In this population, the prevalence of hypothyroidism is up to 16.1% in middle-aged men, 12.9% in middle-aged women with high total cholesterol and it may justify screening of thyroid disease in hypercholesterolemic patients especially in clinical practice.