What is inositol as a dietary supplement?

Overview

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 coverings) of all cells. It plays a role in helping the liver process fats and in 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 also has 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 milligrams daily.

Therapeutic Dosages

Experimentally, inositol dosages of up to 18 grams (g) daily have been tried for various conditions.

Therapeutic Uses

Inositol has been studied for depression, 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. According to two double-blind studies enrolling almost four hundred people, inositol may help improve various symptoms of polycystic ovary syndrome, including infertility and weight gain. Another small double-blind study found that inositol supplements could help reduce symptoms of psoriasis triggered or made worse by the use of the drug lithium. A small double-blind study failed to find inositol helpful for premenstrual dysphoric disorder, a severe form of premenstrual syndrome.

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

Scientific Evidence

Depression. Small double-blind studies have found inositol helpful for depression. In one such trial, twenty-eight depressed persons were given a daily dose of 12 g of inositol for four weeks. By the fourth week, the group receiving inositol showed significant improvement compared with the placebo group. However, a double-blind study of forty-two people with severe depression that was not responding to standard antidepressant treatment found no improvement when inositol was added.

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 (twenty-one participants)
found that people given 12 g of inositol daily had fewer and less severe panic
attacks compared with the placebo group.

A double-blind, crossover study of twenty people compared inositol to the
antidepressant drug fluvoxamine (Luvox), a medication related to Prozac. The
results of four weeks of treatment showed that the supplement was, at minimum,
just as effective as the drug.

Bipolar disorder. In a six-week, double-blind study, twenty-four
people 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. 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. During the study period of fourteen
weeks, participants given inositol showed improvement in ovulation frequency
compared with those given placebo. Benefits were also seen in terms of weight loss
and levels of HDL (good) cholesterol. A subsequent study of ninety-four women
found similar results. However, both of the studies were performed by the same
research group. Independent confirmation is necessary before inositol can be
considered an effective treatment for PCOS.

Safety Issues

No serious side effects have been reported for inositol, even with a therapeutic dosage that equals about eighteen 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. Persons with bipolar disorder 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 be harmful.

Bibliography

Allan, S. J., et al. “The Effect of Inositol Supplements on the Psoriasis of Patients Taking Lithium.” British Journal of Dermatology 150 (2004): 966-969.

Gerli, S., et al. “Randomized, Double-Blind, Placebo-Controlled Trial: Effects of Myo-Inositol on Ovarian Function and Metabolic Factors in Women with PCOS.” European Review for Medical and Pharmacological Sciences 11 (2007): 347-354.

Nemets, B., et al. “Myo-Inositol Has No Beneficial Effect on Premenstrual Dysphoric Disorder.” World Journal of Biological Psychiatry 3 (2002): 147-149.

Palatnik, A., et al. “Double-Blind, Controlled, Crossover Trial of Inositol Versus Fluvoxamine for the Treatment of Panic Disorder.” Journal of Clinical Psychopharmacology 21 (2001): 335-339.