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.

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 . 1-4

Inositol has also been studied for bipolar disorder , 5panic disorder , 6,7bulimia , 8 and obsessive-compulsive disorder , 9,10 but the evidence remains far from conclusive. Other potential uses include Alzheimer's disease11 and attention deficit disorder . 12

According to two double-blind studies enrolling a total of almost 400 people, inositol may help improve various symptoms of polycystic ovary syndrome , including infertility and weight gain. 31,33

Another very small double-blind study found that inositol supplements could help reduce symptoms of psoriasis triggered or made worse by use of the drug lithium . 32

A small double-blind study failed to find inositol helpful for premenstrual dysphoric disorder, a severe form of premenstrual syndrome (PMS) . 30

Inositol is sometimes proposed as a treatment for diabetic neuropathy , but there have been no double-blind, placebo-controlled studies on this subject, and two uncontrolled studies had mixed results. 13,14

Inositol has also been investigated for potential cancer-preventive properties. 15-22

What Is the Scientific Evidence for Inositol?

Depression

Small double-blind studies have found inositol helpful for depression . 23,24 In one such trial, 28 depressed individuals were given a daily dose of 12 g of inositol for 4 weeks. 25 By the fourth week, the group receiving inositol showed significant improvement compared to the placebo group.

However, 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. 26

Panic Disorder

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. 27

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.

Bipolar Disorder

In a 6-week, double-blind study, 24 individuals with bipolar disorder received either placebo or inositol (2 g three times daily for a week, then increased to 4 g three times daily) in addition to their regular medical treatment. 5 The results of this small study failed to show statistically significant benefits; however, promising trends were seen that suggest a larger study is warranted.

Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a chronic endocrine disorder in women that leads to infertility, weight gain, and many other problems. In a double-blind, placebo-controlled trial, 136 women with PCOS were given inositol at a dose of 100 mg twice daily, while 147 were given placebo. 31 Over the study period of 14 weeks, participants given inositol showed improvement in ovulation frequency as compared to those given placebo. Benefits were also seen in terms of weight loss and levels of HDL ("good") cholesterol. A subsequent study of 94 people found similar results. 33 However, both of the studies were performed by the same research group. Independent confirmation will be necessary before inositol could be considered an effective treatment for PCOS.

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. 29 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 very large doses, it is important to purchase a reputable product, because a contaminant present even in small percentages could add up to a real problem.