Secretion of thyrotropin and thyroid hormone
is slightly increased in morbidly obese subjects
(July 2006)
The background of the study. There is a positive
association between thyrotropin (TSH) secretion within the normal
range and body-mass index, but the relationships between TSH and
thyroid hormone secretion are unclear. In this study, thyroid function
was assessed and the relationships between thyroid function and
insulin sensitivity were evaluated in subjects with morbid obesity.
How the study was done. The study subjects were
78 subjects with morbid obesity (body-mass index >40 kg/m2) who
had normal serum TSH, total and free thyroxine (T4), total and free
triiodothyronine (T3), and antithyroid peroxidase antibody concentrations.
They and 77 age- and sex-matched normal-weight subjects had measurements
of height, weight, waist circumference, and fat and lean body mass.
An oral glucose-tolerance test was performed in 49 of the morbidly
obese subjects, and their sensitivity to insulin was measured.
The results of the study. The 78 subjects with
morbid obesity and normal thyroid function had higher serum TSH,
total T4, total T3, and free T3, but not free T4, concentrations,
as compared with the normal subjects (Table). There was no correlation
between the subjects’ serum TSH concentrations and body-mass
index, fat mass, lean body mass, or waist circumference.
| Table. Mean Serum TSH and Thyroid Hormone Concentrations
in Morbidly Obese and Normal-Weight Subjects. |
| Serum |
Morbid Obesity
(n = 78) |
Normal-Weight
(n = 77) |
P Value |
| TSH (mU/L) |
2.0 |
1.7 |
<0.05 |
| Total T4 (µg/dl) |
8.7 |
7.6 |
<0.01 |
| Free T4 (ng/dl) |
1.2 |
1.3 |
>0.05 |
| Total T3 (ng/dl) |
154 |
110 |
<0.01 |
| Free T3 (ng/dl) |
0.37 |
0.33 |
<0.05 |
Among the 49 morbidly obese subjects who had glucose-tolerance
tests, 71 percent had normal glucose tolerance and 29 percent had
impaired glucose tolerance. In the subjects with normal glucose
tolerance, serum TSH concentrations were positively correlated with
fasting serum insulin concentrations and with insulin resistance.
The conclusions of the study. Serum TSH and thyroid
secretion concentrations are slightly higher in morbidly obese subjects
than in normal-weight subjects, suggesting resistance of TSH secretion
to the inhibitory action of T4 and T3.
The original article. Michalaki MA, Vagenakis
AG, Leonardou AS, Argentou MN, Habeos IG, Makri MG, Psyrogiannis
AI, Kalfarentzos FE, Kyriazopoulou VE. Thyroid function in humans
with morbid obesity. Thyroid 2006;16:73-8.
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