Relationship between Thyroid Dysfunction and Serum Low-density Lipoprotein Cholesterol Levels in Subjects Undergoing Annual Health Examination in Japan

Abstract

Objective: A limited number of epidemiological studies have attempted to assess thyroid function and coronary artery disease (CAD) risk factors in the general population. We attempted to clarify relationships between underlying thyroid dysfunction and serum low-density lipoprotein cholesterol (LDL-C) levels in subjects undergoing annual health examination in Japan. Methods: Of 2 , 727 subjects who visited Tokai University Hachioji Hospital for annual health examination, 1 , 434 men and 1 , 065 women were included in this study. Subjects on medication for dyslipidemia, and those with a prior history of thyroid disease or CAD were excluded. We classifie d thyroid function based on serum thyrotropin (TSH) concentrations. Results: LDL-C levels in subjects with low TSH were lower than those in subjects with normal TSH. On the other hand, no difference in LDL-C levels was observed in subjects with high TSH. In females aged 55 and above, more than 40 % had high LDL-C levels, and more than 10 % had a high TSH concentration. Moreover, for this subject group, the percentage achievement of treatment goals gradually declined in pace with increasing TSH levels, going from low, through normal, to high. Specifi cally, more than half of the female subjects in this age group with high TSH did not achieve their treatment goals. Conclusion: Th e results of our study to assess whether high LDL-C is due to thyroid dysfunction suggest that female subjects aged 55 years and above with LDL-C ≥ 140 mg/dL should receive thyroid function tests. Keyword thyroid function, low-density lipoprotein cholesterol, TSH