Inositol is a simple carbohydrate that was originally thought to be essential to good health, but has since been demonstrated not be a vitamin. In the body, inositol is metabolized into phosphatidylinositol, which then acts as a second messenger system to stimulate the release of calcium from its intracellular storage site in the endoplasmic reticulum. The sugar has also been implicated in improving the transmission of neural signals in individuals afflicted with diabetic nerve damage and numbness. Major sources of inositol include beans, citrus fruit, nuts, rice, veal, pork, and wheat germ. There are no known deficiency symptoms in humans.