What to watch with FT4 and Schlaf?

Thyroid function, particularly free thyroxine (FT4), is well-known to influence sleep. Low FT4 levels (hypothyroidism) can cause fatigue, lethargy, and increased sleep need, while elevated FT4 (hyperthyroidism) often leads to insomnia, restless sleep, and frequent awakenings. However, the relationship is not straightforward: even normal FT4 can be associated with sleep issues due to other factors like stress or cortisol. Consumer biomarker tests (e.g., MyBody-X) can flag FT4 values, but they lack clinical context and should not replace a doctor's evaluation. If FT4 is outside the reference range, a full thyroid panel (TSH, fT3, antibodies) and sleep assessment are recommended. Evidence for the FT4-sleep link is based on clinical practice and observational studies, not high-quality interventional trials. Therefore, any recommendations should be conservative: monitor symptoms, maintain good sleep hygiene, and consult a healthcare professional for abnormal results.