Vitamins D3 & K2, along with Vitamin C, are universally considered as two of the most important nutrients for supporting and positively influencing a wide range of important bodily functions. Perhaps the most important of those functions is maintaining a strong defense system. With EnDuro D your body receives efficacious amounts of both D3 and K2. Endurance C is unlike your typical vitamin C supplement, as it contains several other nutrients/compounds that complement vitamin C perfectly. This two-product combination protects and supports a strong defense system all year long!