A study conducted by researchers at the Federal University of São Paulo with participants from the São Paulo Epidemiological Sleep Study found that people with hypothyroidism experience a higher frequency and severity of obstructive sleep apnea. The findings, published in May in the journal Sleep, showed that patients receiving hormone replacement therapy for thyroid dysfunction slept longer and spent more time in deep sleep.
Researchers analyzed data from 761 residents who underwent laboratory tests and polysomnography. Hypothyroidism was identified in 12.6% of the sample, nearly half of whom had obstructive sleep apnea. Ellen Maria Sampaio Xerfan, first author of the study, said, "We expected the prevalence of sleep apnea to be considerable among people with hypothyroidism, but the result was higher than we'd imagined. Studies in the literature typically report figures averaging between 30% and 40%, but we found that nearly half of our participants had both conditions."
Hypothyroidism is characterized by insufficient production of hormones by the thyroid gland, affecting metabolism and other bodily functions. The most common cause is Hashimoto's thyroiditis. Symptoms include fatigue, weight gain, hair loss, dry skin, constipation, and difficulty concentrating. Estimates suggest that 4% to 8% of people are affected by hypothyroidism.
Obstructive sleep apnea occurs when there are repeated interruptions in breathing during sleep due to airway blockage. It can lead to snoring, daytime sleepiness, difficulty concentrating, and an increased risk for cardiovascular diseases.
Xerfan said there is a complex interaction between thyroid function and sleep quality: "Sleep and the thyroid are linked to fundamental mechanisms of homeostasis. There's a complex interaction between the two systems, and sleep disturbances can influence hormonal regulation just as thyroid dysfunction can affect sleep quality." The study also found a possible bidirectional relationship: characteristics associated with poorer sleep quality were linked to a higher likelihood of hypothyroidism.
Monica Levy Andersen advised integrating evaluation for both conditions into clinical practice: "Today, when a patient seeks care... it isn't always considered that a sleep disorder might be contributing to these symptoms." She added that while treating one condition may improve certain parameters for the other, "the evidence suggests that treating hypothyroidism may improve certain sleep parameters... They're two distinct conditions that can interact and amplify cardiovascular risks." Researchers plan further studies using follow-up data from EPISONO participants.
