Thyrotropin and body mass index, are they related?

It is well recognized that overt thyroid dysfunction is associated with changes in body mass index (BMI). However, there is ongoing debate regarding the influence of thyroid stimulating hormone (TSH) on BMI, in euthyroid subjects. The aim of this study is to examine the association of TSH with BMI in an outpatient population without evidence of thyroid disease.

Cross-sectional study conducted in an Endocrinology Department. We identified the latest TSH and BMI measurements in 923 patients from the reference euthyroid population. All patients with positive thyroid autoimmunity and nodules were excluded. We performed a linear regression analysis using SPSSv.025.

923 adult patients were evaluated. 79.4% were males, with a mean age of 67.6 years old. Mean TSH level was 1.78 mIU/L and mean BMI was 29.2 kg/m². A significant negative correlation between serum TSH concentration and BMI was evident (p=0.04; r=-0.067). Statistical significance was lost when performing subgroup analysis, for males and females (p=0.19 and p=0.075), elderly (≥65 years) and non-elderly (p=0.55 and p=0.32) and also obese (BMI ≥30 kg/m²) and non-obese (p=0.39 and p=0.13).

The relationship between BMI and TSH is not consensual in the literature. This study included a large cohort sample of euthyroid patients, majority men and with negative autoimmunity. Our results support the hypothesis that variation in thyroid status within the normal range, could have a negative effect on BMI, contrary to most published studies.