Relationship of TSH Levels with Cardiometabolic Risk Factors in US Youth and Reference Percentiles for Thyroid Function

Abstract

Context: Thyroid hormones play an important role in metabolic homeostasis, and higher levels have been associated with cardiometabolic risk. Objective: To examine the association of cardiometabolic risk factors with TSH levels in US youth. Methods: Cross-sectional study of youth aged 12 to 18 years without known thyroid abnormalities from 5 National Health and Nutrition Examination Survey cycles (n = 2818) representing 15.4 million US children. Subclinical hypothyroidism (SH) was defined as thyrotropin (TSH) levels of 4.5 to 10 mIU/L. Assessed cardiometabolic risk factors include abdominal obesity (waist circumference >90th percentile), hypertriglyceridemia (triglyceride ≥130 mg/dL), low high-density lipoprotein cholesterol (<40 mg/dL), elevated blood pressure (systolic and diastolic blood pressure ≥90th percentile), hyperglycemia (fasting blood glucose ≥100 mg/dL, or known diabetes), insulin resistance (homeostatic model for insulin resistance > 3.16), and elevated alanine transferase (≥ 50 for boys and ≥44 U/L for girls). Age and sex- specific percentiles for thyroid parameters were calculated. Results: In this cohort of youth (51.3% male), 31.2% had overweight/obesity. The prevalence of SH was 2.0% (95% CI 1.2-3.1). The median TSH levels were higher in youth with overweight/obesity (P < 0.001). Adjusting for age, sex, race/ethnicity, and obesity, youth with TSH in the fourth quantile had higher odds of abdominal obesity (OR 2.53 [1.43-4.46], P = .002), insulin resistance (OR 2.82 [1.42-5.57], P = .003), and ≥2 cardiometabolic risk factors (CMRF) (OR 2.20 [1.23-3.95], P = .009). Conclusion: The prevalence of SH is low in US youth. The higher odds of insulin resistance and cardiometabolic risk factors in youth with TSH levels >75th percentile requires further study.