Increasing levels of vitamin D3 among the general population could potentially prevent chronic diseases that claim nearly one million lives throughout the world each year. Incidence of several types of cancer could also be slashed in half. Vitamin D fights infections, including colds and the flu, as it regulates the expression of genes that influence your immune system to attack and destroy bacteria and viruses. Feeling tired and achy is a frequent complaint. While many are misdiagnosed as having fibromyalgia or chronic fatigue, these are classic signs of vitamin D deficiency osteomalacia. The remedy is a combination of vitamin D and calcium. Researchers estimate that 50 percent of the general population is at risk of vitamin D deficiency and insufficiency. Among school aged children, that percentage may be as high as 70 percent.