Vitamin D is absolutely essential for good health. Also known as the sunshine vitamin, it is made in your skin when exposed to sunlight. In spite of that, vitamin D deficiency is one of the most common nutrient deficiencies in the world. Up to 42% of the adult population in the US has low vitamin D levels, which can cause health problems. Vitamin D is particularly important for bone health and immune system function. This article discusses how much vitamin D you need.