Relationship of TSH levels with cardiometabolic risk factors in US youth aged 12-18 years and population-based reference percentiles for thyroid function tests

Abstract

Context: Thyroid hormones play an important role in the metabolic homeostasis of the body and have been associated with cardiometabolic risk. Objective: To examine the association of cardiometabolic risk factors (CMRF) with TSH levels in youth at population level in the US. Design & Setting: Cross-sectional study of youth aged 12-18 years without known thyroid abnormalities from National Health and Nutrition Examination Survey 1999-2012. Subclinical hypothyroidism (SH) was defined as TSH levels 4.5-10 mIU/L. Assessed CMRF included abdominal obesity (waist circumference > 90th percentile), hypertriglyceridemia (TG ≥ 130 mg/dL), low HDL cholesterol (HDL-C < 40 mg/dL), elevated blood pressure (SBP and DBP ≥ 90th percentile), hyperglycemia (FBG ≥ 100 mg/dL, or known diabetes), insulin resistance (HOMA-IR > 3.16) and elevated alanine transferase (ALT ≥ 50 U/L for boys and ≥ 44 U/L for girls). Age and sex- specific percentiles for thyroid parameters were calculated for youth with normal weight. 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<.001). Adjusting for age, sex, race/ethnicity and level of obesity, youth with TSH in the 4th quantile had higher odds of abdominal obesity (OR 2.53 [1.43-4.46], p = .002), higher HOMA-IR (OR 2.82 [1.42-5.57], p=.003) and ≥ 2 CMRF (OR 2.20 [1.23-3.95], p=.009). Conclusions: The prevalence of SH is low in US youth. The higher odds of insulin resistance and CMRF in youth with TSH levels > 75th percentile requires further study.