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 justified in patients with hypercholesterolaemia, we determined the prevalence of subclinical hypothyroidism at different levels of total plasma cholesterol 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 participants 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 hypothyroidism was defined as plasma TSH levels higher than 4 mU/l, in the presence of normal free thyroxine (FT4(4)) concentration. RESULTS Plasma samples of a total of 1191 participants were analyzed, The overall 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 cholesterol stratum (P = 0.02). In men, the mean prevalence was 1.8 percent and roughly similar in the various strata, After age correction, an increase of 1 mU/l TSH in women was associated with an increase of 0.09 mmol/l total plasma cholesterol (95% confidence interval (CI) 0.02-0.16 mmol/l). A similar 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 thyroid dysfunction, In men a similar correlation between thyroid dysfunction and total plasma cholesterol is seen, but the prevalence of thyroid dysfunction is considerably lower.