Levo-thyroxine Replacement in Obese Adults: the Role of Metabolic Variables and Aging on Thyroid Testing Abnormalities.

updated at 15:16 by Mele C, Tagliaferri MA, Pagano L, Soranna D, Scacchi M, Aimaretti G, Biondi B, Marzullo P via American Goiter Association

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Levo-thyroxine Replacement in Obese Adults: the Role of Metabolic Variables and Aging on Thyroid Testing Abnormalities.
J Clin Endocrinol Metab. 2019 Jul 02;:
Authors: Mele C, Tagliaferri MA, Pagano L, Soranna D, Scacchi M, Aimaretti G, Biondi B, Marzullo P
Abstract
CONTEXT: General rates of over- and under-replacement in levo-thyroxine (L-T4) users with primary hypothyroidism are variably high. No information on L-T-4 adequacy exists in obesity.
OBJECTIVE: We explored rates and factors relating to L-T4 adequacy in obese patients with primary hypothyroidism.
SETTING: Tertiary care center.
DESIGN: Among 4954 consecutive obese patients admitted between 2011-2014, 691 hypothyroid patients on L-T4 therapy and 691 BMI-, age- and gender-matched euthyroid controls underwent analysis of thyroid function, gluco-lipid profile, body composition and indirect calorimetry. L-T4 users were classified into low TSH (<0.27 mU/liter), euthyroid (0.27-4.2 mU/liter) and high TSH (>4.2 mU/liter).
RESULTS: L-T4 users constituted 13.9% of the incident population. TSH was low in 7.5%, high in 17.2% and normal in 75.2% of L-T4 users. Over-treatment decreased with aging and more L-T4 users ≥65y had normal TSH than those <65y (p<0.05). Compared to the euthyroid obese group, L-T4 users showed higher adiposity, similar insulin resistance but an healthier lipid profile. In multivariable analyses, L-T4 dose was predicted by fat-free mass, hypothyroidism cause, and gender (p<0.0001 to <0.05). Risk of L-T4 over-replacement increased with younger age (OR 0.96; 95% CI 0.94-0.99), higher L-T4 dose (OR 2.98; 95% CI 1.44-6.14) and lower BMI (OR 0.93; 95% CI 0.88-0.99). Male gender increased the likelihood of L-T4 under-replacement (OR 2.37; 95% CI 1.10-5.11).
CONCLUSIONS: Obesity is associated with milder rates of inadequate L-T4 treatment compared to non-obese populations. L-T4 adequacy increases with aging. Age, body composition and gender are main the determinants of L-T4 requirements in obesity.
PMID: 31265068 [PubMed - as supplied by publisher]