A daily regimen of this D3 (cholecalciferol) is the best way to treat and prevent vitamin D deficiency, whether from lack of sunlight, poor nutrition, chronic illness or aging. D3 5000™ offers support for healthy bones by maintaining normal blood levels of calcium and phosphorus, thus promoting calcium absorption. It helps combat fatigue and assists the immune system with cellular growth regulation. An important formulation for those with low levels of vitamin D.