
What is vitamin D3 good for? Vitamin D (ergocalciferol-D2, cholecalciferol-D3, alfacalcidol) is a fat-soluble vitamin that helps your body absorb calcium & phosphorus. Having the right amount of vitamin D, calcium, & phosphorus is important for building & keeping strong bones. Vitamin D3 offers many health benefits. It is known to help strengthen bones & muscles, boost immunity, increase mood, aid in weight loss, & improve heart function.