Feeling tired and mentally fuzzy? You could be suffering from a Vitamin D deficiency. Vitamin D, a fat-soluble vitamin, is a necessary and essential vitamin in maintaining optimum health and energy levels. Our bodies absorb Vitamin D from exposure to sunlight and from diet and supplements. If you have low levels of Vitamin D, it can cause more than lethargy, it can lead to an increased risk for serious diseases, including diabetes, stroke, coronary artery disease and fractures. Many people, especially. Our test can tell you if you’re in the normal or abnormal range. If you have abnormal or low Vitamin D levels, here’s a short list of some of the causes: Obesity Smoking Exposure to air pollution. Diet, including decreased intake of fats or Vitamin D-rich foods. Lack of exposure to sunlight. Renal or liver diseases. Use of certain medications including anticonvulsants, corticosteroids, HIV drugs, and more.