Prevalence of thyroid disease in an older Australian population

Abstract

To determine the prevalence of thyroid disease in an older Australian population in a population-based cross-sectional study. Community-living subjects, aged 49 years or older, in two Blue Mountains postcodes were invited to participate in an eye, nutrition and health study between 1997 and 2000. Three thousand five hundred and nine of the 4489 identified persons participated. Fifty-seven per cent of 3504 who completed questionnaires were women; their mean age was 66.8 years. Thyroid-stimulating hormone (TSH) was measured in 2665 subjects (76% of those completing the questionnaire). The main outcome measures were serum TSH and free thyroxine levels, serum lipids, urate and sugar levels and questionnaire responses. The prevalence of recognized thyroid disease (either self-reported history of thyroid disease or current thyroxine treatment) was 10% (95% confidence interval (CI) 8.9-11.1%). An additional 3.6% (95%CI 2.9-4.3%) of participants had unrecognized thyroid disease (abnormal TSH). The TSH was abnormal in 7.1% (95%CI 5.8-8.4%) of women and 3.7% (95%CI 2.6-4.8%) of men. Sixty-five per cent of those with an abnormal TSH did not report a history of thyroid disease, whereas 25% of those taking thyroxine replacement therapy had an abnormal TSH level. The prevalence of hypothyroidism increased with increasing age in women. The mean fasting cholesterol was 0.36 mmol/L (95%CI 0.15-0.57) higher in hypothyroid subjects than in euthyroid subjects. Thyroid disease in older Australian women is relatively common and may be undiagnosed. Ongoing monitoring of patients on thyroxine replacement therapy is important, given that 25% of treated patients had an abnormal TSH.