For how we live.
In midlife women the usual cause is the menopause transition, where hot flushes and night sweats last a median of seven years. In older adults they are common, mostly benign, and rarely a mortality signal.
When adults see a doctor for new fatigue, fewer than one in ten turn out to have clear physical disease. The common, treatable and often-missed exception is iron deficiency, which drains energy before it causes anaemia.
A randomised trial and a 21-study meta-analysis found thyroid hormone normalised the blood test but left tiredness and symptom scores unchanged. A guideline now advises against routine treatment.
Two randomised trials tested whether thyroid-hormone tablets help women who carry thyroid antibodies but have normal thyroid function and a history of miscarriage or infertility. Live-birth rates did not move.