In Central Europe, the body's own vitamin D production is insufficient, as even in the height of summer, factors such as smog, ozone, window glass, and sunscreen significantly reduce almost all UVB components in sunlight. As a result, most people exhibit a noticeable vitamin D deficiency. Vitamin D plays an important role in calcium and phosphate metabolism, thereby influencing the formation and breakdown of bones. New findings show that vitamin D has even more important functions. People with higher vitamin D levels age more slowly and are better protected against age-related diseases, such as many types of cancer. This guide demonstrates how to successfully compensate for vitamin D deficiency and the fascinating potentials this vitamin possesses.