Prevalence of thyroid disease in an older Australian population

Abstract

Aim: To determine the prevalence of thyroid disease in an older Australian population in a population-based cross-sectional study.

Background: 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.

Methods: 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.

Results: 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.

Conclusion: 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.