Thyroid Hormone Conversion and Sleep Apnea Connection Revealed

The conversion of the thyroid hormone T4 into the active form T3 is essential for normal metabolism; inadequate conversion can cause hypothyroid symptoms even when TSH levels appear normal. A recent study by the Federal University of São Paulo (UNIFESP) examined 761 adults from the São Paulo Epidemiological Sleep Study and found that 12.6% had hypothyroidism, and nearly half of those also suffered from obstructive sleep apnea (OSA). Higher thyroid‑stimulating hormone (TSH) levels were associated with more severe OSA, and the relationship appeared bidirectional, suggesting each condition may exacerbate the other.

These findings highlight the need for comprehensive thyroid testing—including T4‑to‑T3 conversion assessment—and suggest that clinicians should consider screening for sleep‑disordered breathing in patients with hypothyroidism.