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Retinol Binding Protein-4 Elevation Is Associated with Serum Thyroid-Stimulating Hormone Level Independently of Obesity in Elderly Subjects with Normal Glucose Tolerance

Department of Internal Medicine (S.H.C., Y.J.L., Y.J.P., E.J.L., D.J.P., K.S.P., H.C.J., B.Y.C.), Seoul National University College of Medicine, Seoul 151-742, Korea; and Departments of Internal Medicine (S.H.C., Y.J.P., S.L., H.C.J.), Neuropsychiatry (K.W.K.), and Nuclear Medicine (S.E.K.), Seoul National University Bundang Hospital, Seongnam 463-707, South Korea

Address all correspondence and requests for reprints to: Hak C. Jang, M.D., Ph.D., Department of Internal Medicine, Bundang Hospital, Seoul National University College of Medicine, 300 Gumi-Dong, Bundang-Ku, Seongnam-Si, Gyeonggi-Do 463-707, South Korea. E-mail: janghak{at}snu.ac.kr.

Context: Elevated levels of retinol binding protein-4 (RBP4) are positively correlated with insulin resistance, obesity, diabetes mellitus, and cardiovascular disease (CVD). Subclinical hypothyroidism (SCH) has also been associated with CVD; however, the factors linking SCH to CVD are not clear.

Objective: The objective of the study was to evaluate risk factors for CVD in elderly patients grouped according to thyroid function.

Design: 217 subjects (65 yr old) were randomly selected from a population and allocated to a euthyroid group (n = 177) and an SCH group (n = 40) on the basis of plasma concentrations of TSH and free T₄. We included subjects with normal glucose tolerance by a 75-g oral glucose tolerance test and subjects with impaired fasting glucose. We measured anthropometric parameters, levels of fasting glucose and insulin, hemoglobin A_1c, adiponectin, RBP4, lipid profiles, total body fat content, and the area of sc and visceral fat.

Results: The SCH group had higher RBP4 levels than the euthyroid group, irrespective of body mass index and fat content. Subcutaneous and visceral fat areas and total body fat percentage did not differ between groups and were not correlated with RBP4 level. Other CVD risk factors did not differ between groups. RBP4 level was positively correlated with TSH level (r = 0.241, P = 0.001) after adjustment for age, sex, and body mass index.

Conclusions: Plasma RBP4 levels were associated with SCH independent of obesity in elderly subjects with normal glucose tolerance, indicating that RBP4 level could be used as an index of CVD risk in SCH.