The prevalence of subclinical hypothyroidism at different total plasma cholesterol levels in middle aged men and women: a need for case-finding?

OBJECTIVE In order to determine whether screening of thyroid function is ju stified in patients with hypercholesterolaemia, we determined the prevalenc e of subclinical hypothyroidism at different levels of total plasma cholest erol in middle-aged men and women. DESIGN AND METHODS 1200 participants were selected from a population based cross sectional study on risk factors for cardiovascular diseases, The part icipants were divided into three groups: total plasma cholesterol <5 mmol/l , total plasma cholesterol 5-8 mmol/l, total plasma cholesterol >8 mmol/l, Each group was comparable in size and sex distribution. Subclinical hypothy roidism was defined as plasma TSH levels higher than 4 mU/l, in the presenc e of normal free thyroxine (FT4(4)) concentration. RESULTS Plasma samples of a total of 1191 participants were analyzed, The o verall prevalence of subclinical hypothyroidism was 1.9% in men and 7.6% in women of middle age, In women the prevalence of subclinical hypothyroidism increased from 4.0 percent in the lowest, to 10.3 percent in the highest c holesterol stratum (P = 0.02). In men, the mean prevalence was 1.8 percent and roughly similar in the various strata, After age correction, an increas e of 1 mU/l TSH in women was associated with an increase of 0.09 mmol/l tot al plasma cholesterol (95% confidence interval (CI) 0.02-0.16 mmol/l). A si milar trend was found in men (0.16 mmol/l, 95% CI -0.02-0.34 mmol/l), CONCLUSIONS In the population, the prevalence of subclinical hypothyroidism is up to 10 percent in middle aged women with high levels of total plasma cholesterol and may justify case-finding. In these women approximately 0.5 mmol/l of total plasma cholesterol can be attributed to the subclinical thy roid dysfunction, In men a similar correlation between thyroid dysfunction and total plasma cholesterol is seen, but the prevalence of thyroid dysfunc tion is considerably lower.