Vitamin D contributes to the normal functioning of the immune system, the normal absorption and utilization of calcium and phosphorus, and the normal level of calcium in the blood. In addition, vitamin D helps keep bones, teeth and muscles functioning normally. With little sunlight, poor diet and increasing age, vitamin D levels in the body begin to fall and should be taken as a supplement. Lamberts has vitamin D in a large variety: 400IU, 1000IU, 4000IU, drops for children and a special vegan vitamin D3.