Go natural with Nature's Answer Na Liquid Vitamin D-3 4000Iu (1x.5 OZ). Vitamin D is called the "Sunshine Vitamin" because it is produced naturally by the body after exposure to 20 min - 1/2 hour of sunlight. Many people develop deficiencies due to lack of sun exposure, living in cold climates, and other reasons. Research continues to accumulate showing that vitamin D deficiency is widespread, and that this deficiency is linked to a wide range of illnesses. Vitamin D is most well known for its contribution to joint and bone health by helping the body absorb calcium. However, new research is showing that Vitamin D also plays a major role in immune function, and other metabolic processes important for the maintenance of health and well being. It is especially important to maintain adequate Vitamin D levels in children, as we age, and when we are under stress..