Free T3 (Triiodothyronine) is a critical biomarker for longevity, as it reflects the active form of thyroid hormone in the body. Thyroid function plays a key role in metabolism, energy production, and overall health. Maintaining optimal levels of Free T3 is essential for maintaining a healthy weight, optimal energy levels, and overall well-being. As we age, our thyroid function can decline, making it crucial to monitor and support Free T3 levels for longevity. By tracking and optimizing this biomarker, individuals can support their overall health and potentially extend their lifespan. Consulting with a healthcare professional to assess and address Free T3 levels is recommended for those seeking to optimize longevity.