Deficiency of Vitamin D has been linked to bone and joint problems, kidney problems, impaired respiratory function, and tooth decay. Vitamin D malnutrition may also increase susceptibility to several chronic diseases. Vitamin D’s optimal level enhances both immune and thyroid function, and supports maximal sports-performance throughout the year. Vitamin D is naturally produced by the body when exposed to direct sunlight, however actual UV ray exposure and vitamin D synthesis are dependent on many factors (seasons, location, time, age, smog, skin darkness, etc.)