How are FT3 and blood sugar related?

FT3 (free triiodothyronine) is the active thyroid hormone and influences glucose metabolism at multiple levels: it increases basal metabolic rate, promotes glucose uptake into cells, and modulates gluconeogenesis in the liver. Hyperthyroidism (elevated FT3) can therefore lead to elevated blood sugar levels, while hypothyroidism (low FT3) is often associated with reduced insulin sensitivity and impaired glucose tolerance. However, the relationship is not linear – many patients with thyroid dysfunction have normal fasting glucose. The evidence is based on physiological mechanisms and clinical observations, not large randomized trials. FT3 is not measured in typical consumer DNA tests (like MyBody-X); it is a blood biomarker. A single FT3 measurement without other thyroid parameters (TSH, fT4) and without clinical context is not informative for blood sugar regulation. Be cautious of labs marketing FT3 as an 'optimization marker' for blood sugar – the evidence for that is weak.