Vitamin B8
Also known as Inositol.
What is Inositol?
Inositol, unofficially referred to as "vitamin B8," is present in all animal tissues, with the highest levels in the heart and brain. It is part of the membranes (outer linings) 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 have much 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 this reason, 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.
Sources
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.
Therapeutic Dosages
Experimentally, inositol dosages of up to 18 g daily have been tried for various conditions.
Therapeutic Uses
Some but not all studies suggest that high-dose inositol may be useful for depression.
Inositol has also been studied for bipolar disorder, panic disorder, bulimia, and obsessive-compulsive disorder, but the evidence remains far from conclusive. Other potential uses include Alzheimer's disease and attention deficit disorder.
Inositol is also sometimes proposed as a treatment for complications of diabetes, specifically diabetic neuropathy, but there have been no double-blind placebo-controlled studies, and two uncontrolled studies had mixed results.
Inositol has also been investigated for potential cancer-preventive properties.
What Is the Scientific Evidence for Inositol?
Small double-blind studies have found inositol helpful for depression. In one such trial, depressed individuals were given a daily dose of 12 g of inositol for 4 weeks. By the fourth week, the group receiving inositol showed significant improvement compared to the placebo group.
A double-blind study of 42 people with severe depression that was not responding to standard antidepressant treatment found no improvement when inositol was added.
People with panic disorder frequently develop panic attacks, often with no warning. The racing heartbeat, chest pressure, sweating, and other physical symptoms can be so intense that they are mistaken for a heart attack. A small double-blind study (21 participants) found that people given 12 g of inositol daily had fewer and less severe panic attacks as compared to the placebo group.
A double-blind crossover study of 20 individuals compared inositol to the antidepressant drug fluvoxamine (Luvox), a medication related to Prozac.28 The results over 4 weeks of treatment showed that the supplement was at least as effective as the drug.
Safety Issues
No serious ill effects have been reported for inositol, even with a therapeutic dosage that equals about 18 times the average dietary intake. However, no long-term safety studies have been performed.
Although inositol has sometimes been recommended for bipolar disorder, there is evidence to suggest inositol may trigger manic episodes in people with this condition. If you have bipolar disorder you should not take inositol unless under a doctor's supervision.
Safety has not been established in young children, women who are pregnant or nursing, and those with severe liver and kidney disease. As with all supplements used in multigram doses, it is important to purchase a reputable product, because a contaminant present even in small percentages could add up to a real problem.
Functions:
- Lipid (fat) metabolism
- Cholesterol metabolism
- Nerve function
Deficiency symptoms:
- Hair loss
- Constipation
- Eye abnormalities
- High cholesterol
