Millions of people around the world live with hypothyroidism, a condition in which the thyroid gland does not produce enough hormones.
These hormones help control metabolism, body temperature, heart rate, and many other important body functions. When hormone levels fall, people often feel tired, gain weight, have dry skin, feel cold, and struggle to concentrate.
Another common health problem is obstructive sleep apnea, or OSA. This condition causes the airway to become blocked many times during sleep, making breathing stop and start repeatedly throughout the night.
People with sleep apnea often snore loudly, wake up feeling unrefreshed, and experience excessive daytime sleepiness. Untreated sleep apnea can also increase the risk of heart disease, stroke, diabetes, and other serious health problems.
Scientists have long suspected that thyroid problems and sleep disorders may be connected because both affect the body’s normal balance. A new study from the Federal University of São Paulo (UNIFESP) in Brazil provides stronger evidence that the two conditions are closely linked.
The researchers analyzed health information from 761 adults who took part in the São Paulo Epidemiological Sleep Study, also known as EPISONO 2018. Every participant underwent blood tests and an overnight sleep study called polysomnography, which is considered the most accurate way to measure sleep quality and diagnose sleep apnea.
The results showed that 12.6% of the participants had hypothyroidism. Among these people, nearly half also had obstructive sleep apnea. Lead author Ellen Maria Sampaio Xerfan said the team expected to find a connection, but the number of people with both conditions was even higher than earlier studies had suggested.
The researchers found that people with hypothyroidism had poorer sleep overall. They woke up more often during the night, had more fragmented sleep, and were more likely to have moderate or severe sleep apnea than people with normal thyroid function.
Another important finding involved thyroid-stimulating hormone, or TSH. Higher TSH levels, which often indicate poorer thyroid function, were linked to more severe sleep apnea. The researchers also found the reverse pattern, with people who had worse sleep and more severe apnea being more likely to have hypothyroidism.
This two-way relationship suggests that the two conditions may influence one another. However, the researchers say the study cannot prove which condition develops first because it only looked at participants at one point in time.
The study also examined treatment. People who were taking levothyroxine hormone replacement therapy slept about 49 minutes longer each night than untreated patients. They also spent about 22 more minutes in deep sleep, the stage that is important for physical recovery, tissue repair, and memory.
The researchers believe these findings highlight the importance of checking both thyroid health and sleep quality. Treating hypothyroidism may improve some aspects of sleep, but it does not replace proper testing and treatment for sleep apnea because the two conditions require different medical care.
The study was published in the journal SLEEPJ.
Overall, this was a large community-based study that used high-quality sleep testing, making its findings more reliable than studies based only on questionnaires. However, because it was observational, it cannot prove cause and effect.
Future research that follows people over many years will help determine whether treating one condition can reduce the risk or severity of the other. The findings nevertheless suggest that doctors should consider screening patients with hypothyroidism for sleep apnea and vice versa.
Source: Federal University of São Paulo (UNIFESP).
