Thyroid stimulating hormone is associated with metabolic syndrome in euthyroid postmenopausal women
Introduction
Cardiovascular disease (CVD) is the leading cause of death in women, especially postmenopausal women [1]. It is generally well accepted that hypothyroidism and metabolic syndrome (MetS) are both associated with increased risk for CVD. MetS, which describes a cluster of cardiovascular risk factors including obesity, atherogenic dyslipidemia, hypertension, and insulin resistance, increases the risk of developing CVD [2]. Overt hypothyroidism, with its accompanying hypercholesterolemia and hypertension, is associated with CVD [3], [4].
It has long been observed that thyroid dysfunction is associated with various cardiovascular risk factors and that these risk factors are similar to the components of MetS. Therefore, thyroid dysfunction may have an impact on the prevalence of MetS. However, most cardiovascular events occur in subjects with normal thyroid function, and conflicting results have been reported about the association between thyroid stimulating hormone (TSH) at the upper limit of the normal range and cardiovascular risk factors [5], [6], [7]. In many women, features of MetS such as abdominal adiposity, insulin resistance, and dyslipidemia develop with the transition from pre- to postmenopause [8], [9], [10], [11], [12], [13]. Thus, the question of whether there is an association between thyroid function and MetS in euthyroid postmenopausal women is important. There have been only a few studies on the effects of TSH on the prevalence of MetS. We investigated the association between serum TSH level and the prevalence of MetS and its components and serum lipids in euthyroid Korean postmenopausal women.
Section snippets
Subjects and measurement
The study population consisted of 2205 Korean postmenopausal women who were self-referred for a routine health check-up at Korea University Anam Hospital (Seoul, Korea) from November 2006 to November 2007. All participants were interviewed and examined by the attending gynecologist. Menopause was defined as cessation of menstruation for more than 1 year. The Ethics Committee of our institution approved this study and all subjects provided written consent.
To avoid the influence of confounding
Results
Table 1 displays the baseline characteristics of the study subjects. The mean age was 58.76 ± 5.97 years and the mean TSH level was 1.79 ± 1.59 mIU/L. We evaluated the association between TSH and cardiovascular risk factors, including the components of MetS. In simple correlation analysis, TSH was positively correlated with diastolic blood pressure, total cholesterol, LDL-C and triglycerides (Table 2). Using a multiple linear regression model, LDL-C (β = 0.105; P = 0.004) and triglycerides (β = 0.089; P =
Discussion
We found that TSH levels were associated with MetS in euthyroid postmenopausal women independently of well-known MetS risk factors (age, YSM, BMI, HOMA-IR, life style factors). TSH levels were positively correlated with diastolic blood pressure, total cholesterol, LDL-C and triglycerides. Moreover, LDL-C and triglycerides were independently associated with TSH. Finally, subjects with high normal TSH levels had a 1.95-fold increased risk of MetS, as compared to those with low normal TSH levels.
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