Vitamin D lived a rather humdrum existence until the past decade, shrouded in mystery — there continues a debate as to whether it is really a vitamin or more like a hormone — and largely ignored but for unexciting conversations about bone density, kidney failure and hyperparathyroidism. Not exactly New York Times lead health page material. Then, all that changed. It became possible to test vitamin D levels with a readily available lab test. Studies started coming out suggesting that vitamin D was a key to health. Physicians were told that some 60-80% of adults were deficient in vitamin D, with D3 levels under the cut-off of 30 ng/ml. More importantly, these deficiencies were linked to cancer, neurologic disease, immune dysfunction, and heart disease – not just poor bone health. Large scale screening began, especially among the elderly, and what we doctors found confirmed the studies: most people, even in sunny Hawaii, have suboptimal levels of vitamin D. But what to do with this information?