Thyroid dysfunction in ambulatory elderly Chinese subjects in an area of borderline iodine intake

Thyroid dysfunction has been reported to occur in 10% of the elderly population in Caucasians. As the nature and prevalence vary tremendously between ethnic groups, and no data are available for Chinese, a primary thyrotropin (TSH) screening program using a supersensitive TSH assay was performed on 1880 ambulatory elderly southern Chinese aged above 60 in Hong Kong, an area of borderline iodine intake. Full thyroid function testing was performed on 600 randomly selected samples with normal TSH values and also on subjects with abnormal TSH levels. The results showed that TSH decreased with age in women (p < 0.05) but not in men. The median values for TSH for women 60-69, 70-79, and > 80 years old were 1.40, 1.30, and 1.20, respectively, while for men it was 1.30 mIU/L. Elevated TSH values (> 5.0 mIU/L) were found in 19 (1.0%) while suppressed TSH values (< 0.1 mIU/L) were present in 28 (1.5%) subjects. Biochemical hypothyroidism and hyperthyroidism were present in 3 and 12 subjects, respectively. Two-thirds of the subjects with abnormal TSH values had antithyroid antibodies. Full assessment of the 600 subjects revealed the prevalence rates for antithyroglobulin and antithyroid peroxidase antibody of 10.2 and 11.2%, respectively. Those who were positive for antithyroid antibodies had significantly higher TSH levels (p < 0.005). Free T4 decreased (p < 0.01) while free T3 increased (p < 0.001) with age in the females resulting in higher free T3/free T4 ratio with aging (p < 0.001). This, however, was not seen in the males. In conclusion, thyroid dysfunction in elderly Chinese occurs predominantly in the female. The cause could be explained by both autoimmune thyroid disease as well as iodine insufficiency.