Inositol, unofficially referred to as "vitamin B 8," is present in all animal tissues, with the highest levels in the heart and brain. It is part of the membranes (outer coverings) of all cells, and plays a role in helping the liver process fats as well as contributing to the function of muscles and nerves.

Inositol may also be involved in depression. People who are depressed may have lower than normal levels of inositol in their spinal fluid. In addition, inositol participates in the action of serotonin, a neurotransmitter known to be a factor in depression. (Neurotransmitters are chemicals that transmit messages between nerve cells.) For these two reasons, inositol has been proposed as a treatment for depression, and preliminary evidence suggests that it may be helpful.

Inositol has also been tried for other psychological and nerve-related conditions.

Inositol is not known to be an essential nutrient. However, nuts, seeds, beans, whole grains, cantaloupe, and citrus fruits supply a substance called phytic acid (inositol hexaphosphate, or IP6), which releases inositol when acted on by bacteria in the digestive tract. The typical American diet provides an estimated 1,000 mg daily.