To avoid vitamin D deficiency, get at least 20 minutes of midday sunlight exposure daily and eat wild salmon, free range eggs, organic butter, and oysters regularly. Vitamin D is essential for the proper absorption of calcium, magnesium and iron, the regulation of blood pressure and blood sugar, and the production of vital hormones. Vitamin D deficiencies are prevalent in the winter months because we are typically exposed to less natural sunlight during this time. The UV light from the sun reacts with oils in the skin to promote the synthesis of Vitamin D.