Energy = Health Dietary Supplement Vitamin D functions as a hormone, a chemical messenger with widespread effects in the human body. It is important for optimal bone, cardiovascular, neuromuscular, and immune health. Adequate calcium and vitamin D throughout life, as part of a well-balanced diet, may reduce the risk of osteoporosis. Supplementation with vitamin D may be necessary to meet daily needs, since obtaining sufficient vitamin D from natural food sources and sun exposure alone can be difficult. Research shows that vitamin D3 (cholecalciferol) is approximately 87% more potent than vitamin D2 for raising and maintaining vitamin D blood levels.