THYROID FUNCTION STATUS, CARDIOVASCULAR RISK FACTORS AND MORTALITY IN OLDER PERSONS

Gopinath B.^{1, 2}, Wang J.J.^1,³, Kifley A.¹, Leeder S.R.², Mitchell P.¹

¹Centre for Vision Research, Department of Ophthalmology, Westmead Millennium Institute, University of Sydney, NSW, Australia, ²Australian Health Policy Institute, University of Sydney, Sydney, NSW, Australia, ³Centre for Eye Research Australia, Department of Ophthalmology, University of Melbourne, Melbourne, Victoria, Australia

Abstract

Objectives: Cardiovascular diseases are the most frequent causes of mortality, primarily affecting older adults. There is controversy as to whether an abnormal serum thyrotropin (TSH) may represent a novel marker of cardiovascular disease risk. We aimed to assess the relationship between serum thyrotropin (TSH) and free T4 (F T4) with cardiovascular risk factors and whether thyroid dysfunction is a causal factor for subsequent cardiovascular (CV) mortality in older persons from a representative population.
Methods: Thyroid function status was assessed in 1768 (75.7%) persons aged ?55 years enrolled in the Blue Mountains Eye Study during 1997-9. Serum TSH, free thyroxine (FT4), total cholesterol, high-density lipoprotein-C (HDL-C) and triglycerides were measured using commercial kits. Cardiovascular mortality was assessed until December 2005.
Results: No significant associations were found between either serum TSH and FT4 and HDL-C or triglycerides. However, serum TSH was positively associated with total cholesterol (standardised parameter estimate, _*β*_= 0.08, p= 0.01) after age, sex and body mass index (BMI) adjustments. Additionally, serum FT4 levels were negatively associated with total cholesterol (_*β*_= -0.11, p< 0.01) after adjusting for age, sex and BMI. The proportion of cardiac deaths was 2-fold higher in subjects with subclinical hyperthyroidism (10.0%) compared to subjects with normal thyroid function (4.3%). This association was significant after adjusting for age and sex (hazard ratio, HR 4.8, 95% confidence interval, CI 1.17-19.74), but became non-significant after further adjusting for BMI, smoking and other traditional cardiovascular risk factors (HR 3.6, CI 0.49-26.06).
Conclusions: This large prospective study has demonstrated that serum total cholesterol may be dependent on thyroid function status. We found that older persons with thyroid dysfunction did not have a significantly increased risk of CV mortality, this could have been due to either insufficient study power or confounding effect from CV risk factors.