Of all the remarkable nutritional deficiencies prevalent in the United States, Vitamin D, which is really a steroid hormone, is the most ubiquitous. Over the past 50 years Americans have become cave dwellers, avoiding the sun and increasingly using sun block. It is now known that the minimum daily intake of D3 to prevent Alzheimer's as well as many other diseases is 2000 units daily. Optimal may be as high as 50,000! Learn how critical D3 is to the brain, memory, and mood and how its only toxicity, excess calcium, simply means no calcium supplements when on a maximum dose.