Evidence check: FT3 in the context of menopause

FT3 (free triiodothyronine) is the active thyroid hormone. During menopause, declining estrogen can affect the thyroid axis – e.g., via changes in binding proteins or T4-to-T3 conversion. However, FT3 alone is not a reliable marker for thyroid dysfunction in menopause. Clinically, TSH and FT4 are preferred because FT3 fluctuates significantly (e.g., with inflammation, calorie restriction). Evidence for direct genetic influences on FT3 in menopause is weak; most studies are observational and not translatable to single SNPs. Consumer DNA tests for FT3 are not established – FT3 is measured in blood, not genetically predicted. Interpretation should always be done by an endocrinologist, especially with symptoms like fatigue, weight changes, or mood swings. Caution against self-treating with thyroid hormones based on lay interpretations.