To evaluate the prevalence of previously unknown hypothyroidism in adult male and
female patients with a wide range of body mass index (BMI) values, referred to a Sleep
Clinic because of sleep disordered breathing (SDB).
Serum concentrations of thyroid stimulating hormone (TSH) and free thyroxin (fT4),
as well as forced vital capacity (FVC), PaO2, PaCO2, the Epworth sleepiness scale
(ESS), respiratory disturbance index (RDI), loud snoring, and the percentage of total
sleep time (TST) with <90% oxyhemoglobin saturation (TST(saO2<90%)) were measured
in 78 overweight and obese adult subjects with no previous diagnosis of hypothyroidism
(age: 18-72 years). The prevalence of previously undiagnosed subclinical hypothyroidism
in the population as a whole was 11.5%. BMI, TSH and ESS were significantly higher
in the hypothyroid than the euthyroid subjects, but there was no significant between-group
difference in RDI, TST(saO2<90%) or the other investigated variables, including the
prevalence of obstructive sleep apnea (OSA). Among the hypothyroid individuals, BMI,
neck circumference, ESS, RDI and TST(Sao2<90%) were significantly higher in those
with than in those without OSA. Furthermore, there was a clear trend towards a lower
FVC% and higher snoring score in the OSA patients.
Our results demonstrate a higher prevalence of hypothyroidism than that commonly reported
in overweight and obese individuals referred to a Sleep Clinic for polysomnography
because of SDB, thus suggesting that thyroid function should be evaluated in all obese
patients suffering from SDB despite economic concerns.