Raised serum TSH levels in patients with morbid obesity: is it enough to diagnose subclinical hypothyroidism?

Abstract

Objective: Morbid obesity (body mass index (BMI)R40 kg/m 2 ) is associated with thyroid function disturbances, with a high rate of subclinical hypothyroidism (SH) being the most consistently reported. We evaluated the circulating thyroid function parameters in morbid obese patients and related the results to the presence of circulating thyroid antibodies (Thyr-Ab). Design and methods: Morbid obese patients were consecutively enrolled (nZ350). Two control groups were used: control group (CG)1, healthy normo-weight subjects (nZ50); CG2, normo-weight patients with SH (nZ56) matched for TSH with the obese patients with SH. Serum levels of free triiodothyronine (FT 3 ), free thyroxine (FT 4 ), TSH, antithyroglobulin antibodies, and antithyroperoxidase antibodies were measured in all patients. Results: i) Compared with CG1, obese patients having thyroid function parameters in the normal range and negative Thyr-Ab showed significantly higher serum TSH and lower free thyroid hormones levels, but a similar FT 4 /FT 3 ratio; ii) SH was recorded in 13.7% obese patients; iii) compared with CG2, obese patients with untreated SH had a significantly lower rate of positive Thyr-Ab (32.1 vs 66.1%; P!0.005); iv) no gender prevalence was observed in SH obese patients with negative Thyr-Ab; and v) the comparison of the untreated SH patients (obese and normo-weight) with CG1 demonstrated that in SH obese subjects, unlike normo-weight SH patients, the FT 3 levels were significantly lower. This resulted in a normal FT 4 /FT 3 ratio in SH obese patients. Conclusion: Thyroid autoimmunity is not a major cause sustaining the high rate of SH in morbid obese patients. In these patients, the diagnosis of SH itself, as assessed by a raised TSH alone, appears questionable.

Association between serum TSH concentration within the normal range and adiposity

“…Also, the highest correlations in the association between BMI and serum TSH concentration (rZ0.91) was shown among morbidly obese participants (12). In line with these findings, Rotondi et al (30) found higher values of serum TSH among euthyroid morbid obese subjects when compared with euthyroid normal-weight patients and morbidly obese subjects with hypothyroidism showed lower level of anti-TPO. Thus, the authors suggested that the raised serum TSH concentrations, especially in morbid obesity, may be independent of thyroid function.…”

“…The effects of excess body weight on thyroid could differ between lower grades of overweight and morbid obesity (30), which could in part explain the different findings reported by the reviewed studies, because these articles include people with different levels of overweight or obesity that could blur a possible effect of TSH. In addition, the variability in anti-TPO levels could also explain the discrepancy of results among the reviewed studies.…”

Association of Obesity with Hormonal Imbalance in Infertility: A Cross-Sectional Study in North Indian Women

“…These findings can be explained by the fact that obesity is often associated with chronic low inflammatory state and raised TSH levels observed in obese patients could be due to increased levels of circulating antibodies to thyroid. Another independent study evaluating the thyroid status in morbidly obese population also reported raised TSH levels in obese individuals [29]. This may be a cause of alarm as it has been seen that it may be a component leading to metabolic syndrome [30].…”

MECHANISMS IN ENDOCRINOLOGY: The crosstalk between thyroid gland and adipose tissue: signal integration in health and disease

“…Data regarding the circulating concentrations of thyroid hormones are less univocal because the serum levels of FT 3 were reported as increased, unchanged, or decreased. On the other hand, most studies reported a general trend toward low/normal levels of FT 4 in obese subjects (59,60,61,62,63,64,65,66). Lately, the relation between adiposity and serum TSH, FT 3 , and FT 4 was evaluated in a large, representative sample of the adult population from the National Health and Nutrition Examination Survey 2007-2008 (67).…”

“…patients with lower degrees of overweight and those with morbid obesity). Clinical and genetic evidence support the concept that obesity does not represent a continuous entity and that morbid obese patients are likely to harbor a different disease compared with subjects with milder forms of overweight (64). Examination of patients at different caloric intakes, either while overeating or when on a hypocaloric diet, could also account for the discrepant results (1).…”