Mele C, Tagliaferri MA, Pagano L, et al. - Since general rates of over- and underreplacement in levothyroxine (LT4) users with primary hypothyroidism were variably high, researchers analyzed rates and factors relating to LT4 adequacy in obese patients with primary hypothyroidism. Among 4,954 consecutive obese patients admitted between 2011 and 2014, thyroid function, glucolipid profile, body composition, and indirect calorimetry were examined in 691 patients receiving LT4 therapy and 691 BMI-, age-, and sex-matched euthyroid controls. Data reported that LT4 users constituted 13.9% of the incident population. Findings revealed that TSH was low at 7.5%, high at 17.2%, and normal at 75.2% for LT4 users. LT4 users showed higher adiposity, similar insulin resistance compared with the euthyroid obese group, but a healthier lipid profile. Compared with nonobese populations, obesity is related to milder rates of inadequate LT4 treatment. With aging, LT4 adequacy increases. Main determinants of LT4 requirements in obesity are age, body composition, and gender.