Short reportIncreased TSH in obesity: Evidence for a BMI-independent association with leptin
Introduction
Obesity is a major worldwide health problem with an increasing prevalence. In 2013, more than a third of the world's population was either overweight or obesity [1]. Yet, the pathophysiology of the condition remains unclear. Identifying hormonal targets involved in the condition may help in the management of obese patients.
As thyroid hormones are involved in the regulation of energy-balance, evaluation of thyroid function in obese subjects has been widely investigated [2]. It has been previously described that thyroid-stimulating hormone (TSH) was slightly increased in obese populations [3]. However, the exact mechanisms involved in such increased TSH levels, as well as its physiological relevance, are as yet undetermined.
Several authors have suggested that leptin actions could underlie the association between obesity and increased TSH levels [4]. However, to our knowledge, such an association has not been previously reported in an obese population. Thus, the aim of the present study was to determine the associations between body mass index (BMI), TSH and leptin plasma levels in a large cohort of obese subjects, and to evaluate their physiological relevance.
Section snippets
Study population
This was a single-centre, retrospective observational study using prospective recruitment. Consecutive adult subjects hospitalized in the Department of Endocrinology (Diabetes and Nutrition) at Lyon South Hospital in Pierre-Bénite, France, for nutritional evaluation of obesity (BMI > 30 kg/m2) were screened between 2009 and 2011. Plasma leptin and TSH levels were consistently determined during these nutritional checkups. Patients with a previous history of thyroid diseases or bariatric surgery
Results
Characteristics of the study population are presented in Table 1. A total of 160 obese subjects, representing 20% of the study population, exhibited plasma TSH values > 3.80 mIU/L, the upper limit of the normal range, with a mean TSH value of 5.3 ± 0.1 mIU/L for that quintile. To determine the characteristics of this obese population with slightly increased TSH levels, the whole study population was divided into quartiles according to TSH levels (Table 2). Significant differences were observed for
Discussion
The present study provides evidence that TSH levels are significantly, positively and linearly associated with BMI and leptin in a randomly selected obese population. Moreover, TSH variability was mainly explained by leptin independently of BMI, thereby suggesting a link between the hypothalamus–pituitary–thyroid (HPT) axis and adiposity.
Also observed in our study was a weak, but significant, positive correlation between serum TSH levels, on the one hand, and both weight and BMI, on the other.
Disclosure of interest
The authors declare that they have no conflicts of interest concerning this article.
Funding: this research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.
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