Swanson Vitamin D-3 is an essential bone supporting vitamin that works to absorb calcium efficiently in the body. The body manufactures some vitamin D on its own when it is exposed to sunlight, but for people living in the northern latitudes where wintertime sun exposure is limited, the body's natural vitamin D may often be insufficient. Our High Potency Vitamin D-3 capsules tackle this problem by supplying an impressive 1,000 IU of vitamin D-3, the most biologically active fraction of vitamin D.