Five-year incidence and progression of thyroid dysfunction in an older population.
BACKGROUND
Very few studies have assessed both the incidence and progression of thyroid dysfunction in a single older population-based cohort. In this study, we aimed to assess the 5-year incidence, progression and risk factors for development of thyroid dysfunction in an older Australian population.


METHODS
The Blue Mountains Eye Study is a longitudinal population-based cohort study. During 1997-1999, 1768 participants (≥ 55 years) had thyroid function assessed. After excluding participants reporting any form of treatment for their thyroid condition at baseline, 951 participants (91.4%) without thyroid dysfunction and 54 (5.4%) with thyroid dysfunction were re-examined 5 years later. Thyroid dysfunction was defined using serum thyrotropin (thyroid stimulating hormone (TSH)) screen, followed by serum free T4 assessment.


RESULTS
The overall 5-year incidence of thyroid dysfunction was 4.7% (95% confidence interval (CI) 3.4-6.1). Obesity (body mass index ≥ 30 kg/m(2) ) and serum TSH > 2 mIU/L at baseline predicted incident overt hypothyroidism (odds ratio (OR) 4.05, CI 1.74-9.41) and (OR 5.46, CI 1.16-25.67) respectively. The 5-year incidence of subclinical hypothyroidism was significantly higher in women than in men, 2.5% versus 0.7% (P= 0.03). Progression to overt hypothyroidism was observed in 17.9% of subjects with subclinical hypothyroidism over 5 years.


CONCLUSIONS
The 5-year incidence of thyroid dysfunction in this older population was relatively low, and was associated with obesity and serum TSH level > 2 mIU/L at baseline. Over one in six persons with subclinical hypothyroidism progressed to overt thyroid dysfunction over the 5-year period. Our findings highlight the need for appropriate management of subclinical hypothyroidism among older people.
Gopinath
B
B
Centre for Vision Research, Department of Ophthalmology, Westmead Millennium Institute, Victoria, Australia. bamini_gopinath@wmi.usyd.edu.au
Wang
J J
JJ
Kifley
A
A
Wall
J R
JR
Eastman
C J
CJ
Leeder
S R
SR
Mitchell
P
P
D000367:Age Factors; D000368:Aged; D015331:Cohort Studies; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009517:New South Wales / Q000453:epidemiology; D012307:Risk Factors; D013959:Thyroid Diseases / Q000175:diagnosis / Q000453:epidemiology* / Q000473:pathology*; D013960:Thyroid Function Tests / Q000639:trends