Thyroid Function in Humans with Morbid Obesity

Abstract

Morbidly obese subjects may present with abnormal thyroid function tests but the reported data are scarce. Therefore, we studied the thyroid parameters in 144 morbidly obese patients, 110 females and 34 males, to assess the prevalence of hypothyroidism. Eleven percent (11.8%) carried the diagnosis of hypothyroidism and were undergoing levothyroxine (LT4) replacement therapy, 7.7% had newly diagnosed subclinical hypothyroidism, 0.7% had subclinical hyperthyroidism and 7.7% were euthyroid with positive antibodies (anti-thyroid peroxidase antibodies [TPOAb]). From the 144 subjects, we selected a cohort of 78 euthyroid subjects with negative TPOAb, who did not receive LT4 replacement or suppression therapy (the experimental group) and compared them to 77 normal-weight euthyroid subjects, TPOA-negative, matched for age and gender who served as controls. The experimental group had higher serum levels of triiodothyronine (T3), thyroxine (T4), free triiodothyronine (FT3), and thyrotropin (TSH) compared to the control group. Serum TSH concentration was associated with fasting serum insulin levels and insulin resistance but not with serum leptin levels, body mass index (BMI), fat mass, and lean body mass. In conclusion, in morbidly obese individuals, the prevalence of overt and subclinical hypothyroidism was high (19.5%). The morbidly obese subjects have higher levels of T3, FT3, T4, and TSH, probably the result of the reset of their central thyrostat at higher level.

Expression of thyrotropin and thyroid hormone receptors in adipose tissue of patients with morbid obesity and/or type 2 diabetes: effects of weight loss

“…In a large population study conducted in euthyroid patients from Denmark, 3 the body mass index (BMI) was found to be positively associated with serum TSH and inversely related to free tetraiodotyronine (FT 4 ). This finding has been confirmed in other studies, [4][5][6] but not in all. 7 However, in the latter report, study participants were referrals to a thyroid clinic.…”

“…Furthermore, some studies were carried out in overweight individuals, others included morbidly obese individuals. 5 More recent studies have confirmed that diurnal serum TSH levels are significantly increased, if still within the normal range, in obese individuals, and that major weight loss induces a sizeable reduction in TSH and thyroid hormone levels. [8][9][10] It is unknown whether TSH has a role in favoring fat deposition or, on the contrary, whether excessive accumulation of adipose tissue increases TSH secretion.…”

Multi-center study on the prevalence of hypothyroidism in patients with hypercholesterolemia

“…Interestingly, the BMI of patients with subclinical hypothyroidism was significantly higher than euthyroid patients. The serum levels of TSH were higher in obese patients in some studies [37][38][39][40][41] but not in others [42,43]. The reason is still unclear because the BMI of patients with overt hypothyroidism was not different from the others also in our study.…”

Association between serum TSH concentration within the normal range and adiposity

“…The minimum reference value of TSH ranged from 0.17 to 0.5 mU/l, whereas the maximum reference value of TSH ranged from 3.5 to 5.5 mU/l. Anthropometric measures used in the studies included BMI (4-6, 9-30), body weight (15,31,32), waist circumference (9,14,15,23,29,33), waist-hip ratio (9,15), hip (23), body fat percentage (13,15,17,21,23,29,32), subcutaneous (9,15,21,27) and central (21) fat, and fat mass index (fat mass (kg)/height (m)…”