How are IgG and longevity related?

The relationship between IgG (immunoglobulin G) and longevity is not well-established. IgG is a key antibody in the adaptive immune system, and its levels and subclass distribution change with age. Some research suggests that maintaining a diverse IgG repertoire and balanced subclasses may support healthy immune aging, potentially contributing to longevity. However, direct evidence linking IgG levels to lifespan in humans is weak and mostly mechanistic or observational. Direct-to-consumer tests measuring IgG are not clinically validated as longevity biomarkers. Claims that IgG levels predict or determine longevity are speculative and not supported by robust human trials. Evidence level: unclear/mechanistic.