Thyroid hormone levels and thyroid dysfunction of French adults participating in the SU.VI.MAX study

Abnormal thyroid function has important public health consequences. However, the various degrees of thyroid dysfunction remain unsettled. The SU.VI.MAX cohort provided a unique opportunity to conduct a cross-sectional study of abnormal thyroid function in a large representative population of 11256 men and women representing the geographic distribution of the French continental adult population. Thyroid status was measured, in fasting blood samples, at baseline in 1994-1995. Serum thyrotropin (TSH) levels (abnormal < 0.4 mU/l or > or =4.0 mU/l) and free thyroxine (fT4) were both performed in duplicate on the same sample. Subjects with previous or present thyroid diseases or who were taking thyroid hormones or antithyroid drugs (n=920) were excluded (8.1%). Thus, the final study group consisted of 10346 subjects, 4121 men aged 45-60 years (mean +/-SD) (51.8+/-4.7 yrs), 2641 women aged 35-44 years (40.6+/-2.8 yrs), and 3584 women aged 45-60 years (51.4+/-4.4 yrs). Median (2.5th and 97.5th percentiles) for TSH (mU/l) were 1.52 (0.20-4.54) for men, 1.78 (0.22-5.54) for women aged 35-44 years, and 1.96 (0.22-6.80) for women aged 45-60 years. The TSH distribution of women was shifted to the right compared with men. Arithmetic mean fT4 (+/-SD) was 10.7+/-1.7 ng/l (13.8 +/-2.2 pmol/l) for men and 10.9+/-1.8 ng/l (14.0+/-2.3 pmol/l) for women. The prevalence of abnormal TSH values in men, and in women (35-44 yrs and 45-60 yrs) were TSH or =10.0 mU/l 0.2%, 0.4% and 0.7%, respectively. Geometric mean serum TSH and arithmetic mean serum fT4 concentrations showed significant overall inter-regional differences for men and women (p or =45 yrs) (p=0.04) exclusively. Over the age of 45 years, the women: men ratio for unrecognized elevated TSH levels (> or =4.0 mU/l) was 2.82, whereas it was 0.64 for low TSH levels (