What Vitamin Is Inositol? The Surprising Truth About This 'Pseudovitamin'

October 4, 2025 •

4 min read

Although frequently referred to as vitamin B8, inositol is not technically a vitamin because the human body is capable of producing it from glucose. This article clarifies what vitamin is inositol, explaining its classification as a pseudovitamin and exploring its important functions in metabolic and mental health.

Quick Summary

Inositol is a sugar-like compound often mistaken for a B-vitamin. It acts as a cellular messenger, influencing insulin action, metabolic processes, and chemical signals in the brain.

Key Points

Not a true vitamin: Inositol was historically called 'vitamin B8' but is a pseudovitamin because the body can synthesize it from glucose.
Crucial for cellular signals: It acts as a secondary messenger for insulin and other hormones, helping cells communicate and function properly.
Supports hormonal balance: Inositol, particularly myo-inositol, helps regulate hormones and improve ovarian function, offering benefits for women with PCOS.
Helps manage metabolic conditions: By improving insulin sensitivity, inositol can help manage blood sugar, cholesterol, and other factors linked to metabolic syndrome.
Impacts mental health: Research suggests a link between inositol and mood-regulating neurotransmitters like serotonin, potentially helping with panic disorder and other mood-related issues.
Found in many foods: Natural sources of inositol include fruits (citrus, cantaloupe), whole grains, nuts, and legumes.
Requires mindful supplementation: Inositol may cause mild side effects and should be supervised by a healthcare provider, especially for those with existing health conditions.

Unpacking the 'Vitamin B8' Label

Inositol has long been associated with the B-vitamin family, leading to its nickname, 'vitamin B8'. However, this classification is inaccurate. A true vitamin is an essential nutrient that the body cannot produce on its own and must be obtained through diet. The body, specifically the kidneys and liver, can synthesize inositol from glucose, meaning it is not an essential nutrient. Instead, inositol is more accurately described as a pseudovitamin—a substance with important, vitamin-like functions, but which the body can make.

The Two Primary Forms of Inositol

Inositol exists in nine different forms, or stereoisomers, but the two most biologically significant types for health and supplementation are myo-inositol (MI) and D-chiro-inositol (DCI).

Myo-inositol: This is the most common form found in the body and is crucial for cellular signaling and hormone function, particularly involving follicle-stimulating hormone (FSH). It is abundant in the brain and central nervous system.
D-chiro-inositol: Produced in the body by converting myo-inositol, DCI helps to mediate insulin signaling and regulate glucose metabolism. The conversion of MI to DCI is impaired in conditions like insulin resistance, which can lead to an imbalance.

Both forms are critical for health, and supplementation often uses a combination of the two, typically in a physiological 40:1 ratio of MI to DCI, which has been shown to be effective for conditions like Polycystic Ovary Syndrome (PCOS).

Inositol's Role in Cellular Communication

As a crucial component of cell membranes, inositol acts as a secondary messenger for various hormones, ensuring messages are transmitted efficiently within cells. This plays a major role in several bodily functions:

Insulin Signaling: Inositol helps cells respond effectively to insulin, the hormone that regulates blood sugar. In cases of insulin resistance, inositol's mechanism is compromised, leading to higher blood sugar levels.
Neurotransmitter Regulation: It influences chemical messengers in the brain, such as serotonin and dopamine, which are vital for regulating mood. This connection has sparked research into inositol's potential for improving symptoms of mental health conditions like depression and anxiety.
Hormonal Balance: Particularly in women's health, inositol helps regulate hormones related to the menstrual cycle and ovulation. This makes it a valuable tool in managing hormonal imbalances seen in conditions such as PCOS.

Health Benefits and Considerations

Inositol has been studied for its potential benefits in several areas:

Polycystic Ovary Syndrome (PCOS): Myo- and D-chiro-inositol supplementation has shown promise in improving symptoms associated with PCOS, including improved insulin sensitivity, reduced androgen levels, and restored ovulation. Some studies have found that inositol can help induce ovulation in many women with PCOS.
Metabolic Syndrome: Inositol may help control risk factors for metabolic syndrome, such as high blood pressure and triglycerides, by improving insulin action. Research has shown improvements in metabolic markers for women with the syndrome after supplementing with inositol.
Mental Health Support: Some studies suggest that inositol can help balance mood-related brain chemicals. For example, individuals with anxiety or depression have sometimes shown lower brain inositol levels. Inositol may potentially reduce the frequency of panic attacks, though more research is needed for conditions like depression and anxiety.
Gestational Diabetes: Supplementation with inositol during pregnancy has been investigated for its ability to reduce the risk of developing gestational diabetes.

Myo-Inositol vs. D-Chiro-Inositol: A Comparison

To highlight their unique roles, here is a comparison of myo-inositol and D-chiro-inositol:


Feature	Myo-Inositol (MI)	D-Chiro-Inositol (DCI)
Primary Function	Improves cellular signaling, crucial for FSH and ovulation.	Mediates insulin action and regulates glucose metabolism.
Bodily Abundance	Most abundant form in the human body (approx. 99%).	Produced by converting MI; much less abundant.
Tissue Concentration	High concentrations in the brain and ovaries.	Higher concentrations in tissues that store glycogen, like the liver and fat.
Role in PCOS	Supports healthy ovulation and egg quality by facilitating FSH signaling.	Regulates androgen production; too much can impair egg quality.
Supplementation	Most common standalone supplement; often combined with DCI.	Often taken in conjunction with MI in a 40:1 ratio for synergistic effects.

Dietary Sources and Supplementation

While the body produces its own inositol, it is also present in a wide variety of foods. Incorporating these into your diet can help support overall health:

Fruits: Citrus fruits (oranges, grapefruit), cantaloupe, and peaches are good sources.
Grains: Whole grains, brown rice, and wheat bran contain inositol.
Nuts and Seeds: Almonds, walnuts, and peanuts are rich in inositol.
Legumes: Beans, such as lima and navy beans, provide a good amount.
Organ Meats: Liver and kidney meat are particularly rich sources.

For therapeutic benefits in conditions like PCOS or metabolic syndrome, the amount of inositol obtained from food alone is often insufficient, necessitating supplementation. It is important to consult with a healthcare provider before beginning any new supplement.

Possible Side Effects and Precautions

Inositol supplements are generally well-tolerated, especially at lower intakes. However, some mild side effects have been reported with higher intakes. These can include:

Nausea
Gas or diarrhea
Stomach discomfort
Dizziness or headaches

It is crucial for individuals with specific health conditions to consult a doctor before supplementing. For instance, high amounts are not recommended for people with bipolar disorder, as they could potentially induce manic episodes. Inositol can also affect blood sugar levels, so diabetics should monitor their blood glucose closely when starting supplementation.

Conclusion

In summary, while once incorrectly labeled vitamin B8, inositol is a naturally occurring, sugar-like substance essential for numerous biological functions. It plays a critical role as a cellular messenger, influencing insulin sensitivity, hormonal balance, and neurotransmitter activity. The two main forms, myo-inositol and D-chiro-inositol, work synergistically and are particularly beneficial for conditions like PCOS and metabolic syndrome. Available through dietary sources and supplements, inositol offers a promising pathway for supporting metabolic and mental wellness, provided it is used with proper medical guidance. For more detailed information on its metabolic functions, authoritative resources are available.

Frequently Asked Questions

No, despite being previously referred to as 'vitamin B8,' inositol is not a true vitamin. The body can produce it naturally, while vitamins are essential nutrients that must be obtained from the diet.

Myo-inositol (MI) and D-chiro-inositol (DCI) are the two main forms. MI is more common and crucial for cellular messaging, while DCI mediates insulin signaling and glucose metabolism. They often work best in a 40:1 ratio for optimal effects, particularly for conditions like PCOS.

Good dietary sources of inositol include fruits (oranges, cantaloupe), nuts (almonds, walnuts), legumes (beans), whole grains, and organ meats like liver.

Yes, supplementation with a combination of myo-inositol and D-chiro-inositol can help improve PCOS symptoms. It has been shown to improve insulin sensitivity, reduce androgen levels, and restore menstrual cycles and ovulation.

Inositol is generally safe, but higher intakes can cause mild side effects such as nausea, gas, diarrhea, headaches, and dizziness. It's best to start with a lower amount and increase gradually under medical guidance.

Inositol plays a role in the function of neurotransmitters like serotonin and dopamine, which influence mood. Some studies suggest it may help with certain mental health conditions, such as panic disorder, though more research is needed.

The way inositol supplements are taken can vary depending on the health condition being addressed, and they are often taken in split doses. It is important to consult a healthcare provider to determine the appropriate approach for your needs, especially if you have pre-existing conditions like diabetes.