Which B Vitamin Is Inositol? Unpacking the Truth About the Pseudovitamin

October 4, 2025 •

4 min read

Although it was once called Vitamin B8, inositol is not officially a B vitamin. The body can naturally produce this intriguing compound from glucose, which is why it was reclassified as a "pseudovitamin". This brings to light the common question, which B vitamin is inositol, and highlights its significant role in human health despite its non-essential status.

Quick Summary

Inositol, previously mistaken for vitamin B8, is a vitamin-like carbohydrate produced by the body. This article clarifies its true nature, exploring its vital functions in insulin signaling, mental health, and cellular processes, along with key dietary sources and supplement uses for conditions like PCOS and metabolic syndrome.

Key Points

Not a B Vitamin: Inositol was historically called Vitamin B8 but is no longer classified as a vitamin because the body can synthesize it from glucose.
A Pseudovitamin: It is now known as a vitamin-like carbohydrate, or pseudovitamin, that plays essential roles in cellular signaling and function.
Exists in Different Forms: The most studied supplemental forms are myo-inositol (MI) and D-chiro-inositol (DCI), which act differently in the body.
Supports Insulin Sensitivity: Inositol helps improve the body's response to insulin, benefiting those with metabolic syndrome, PCOS, and diabetes.
May Improve Mental Health: It influences neurotransmitters like serotonin, showing promise for anxiety, panic disorder, and OCD in some studies.
Found in Many Foods: Natural sources include fruits, grains, nuts, and beans, though supplements offer higher therapeutic doses.
Generally Safe: Supplements are typically well-tolerated, with mild and temporary gastrointestinal side effects possible at higher doses.

The Inositol Identity Crisis: Why It's No Longer a B Vitamin

For many years, inositol was included in the B-vitamin complex and referred to as vitamin B8. This classification was based on its important functions and its presence in foods often associated with B vitamins. However, scientific advancements revealed a crucial distinction: unlike true B vitamins, inositol is not an essential nutrient that must be solely obtained from the diet. The human body, specifically the kidneys and liver, can synthesize its own supply from glucose.

Because a nutrient must be obtained externally to be considered a vitamin, inositol was declassified and is now known as a "pseudovitamin" or vitamin-like substance. Its status as a carbohydrate with vitamin-like properties allows it to play vital roles in metabolic processes and cellular communication without being a formal member of the vitamin family.

The Body's Inositol Production

The body's ability to produce its own inositol is a key factor in its reclassification. The kidneys alone can produce up to 2 grams of myo-inositol per day. This is in addition to the amount obtained from a typical diet, which provides around 0.5 to 1.0 grams daily. Endogenous production, along with dietary intake, is generally sufficient to meet the body's baseline needs, explaining why a clinical deficiency is rare.

The Different Faces of Inositol: Myo- and D-Chiro-Inositol

Inositol isn't a single molecule but rather a family of nine different isomers, which are molecules with the same chemical formula but different arrangements. The two most biologically significant forms, especially for supplemental use, are myo-inositol (MI) and D-chiro-inositol (DCI). These two forms are involved in distinct but complementary biological pathways.

A Tale of Two Isomers


Aspect	Myo-Inositol (MI)	D-Chiro-Inositol (DCI)
Primary Function	Involved in follicular-stimulating hormone (FSH) signaling and facilitates cellular glucose uptake.	Primarily involved in glycogen synthesis, storage, and the disposal of excess glucose.
Abundance	The most abundant form of inositol in the body, making up about 99% of its total inositol.	Less abundant, as it is produced via the conversion of myo-inositol by the epimerase enzyme.
PCOS Ratio	Optimal levels are crucial for healthy ovarian function and egg quality.	Excessive DCI, particularly in the ovaries, can have a detrimental effect on egg quality and hormonal balance.
Supplemental Use	Often used in higher doses, sometimes paired with folic acid, for fertility and metabolic conditions.	Often combined with MI in a specific ratio (like 40:1) to mimic the body's natural balance.

Key Health Benefits of Inositol

Though not a vitamin, inositol provides significant health benefits, often studied in high-dose supplemental form for specific conditions:

Improving Insulin Sensitivity: Inositol acts as a second messenger in insulin signaling, helping the body's cells respond more effectively to the hormone. This makes it beneficial for conditions linked to insulin resistance, such as polycystic ovary syndrome (PCOS), metabolic syndrome, and type 2 diabetes. For example, studies suggest inositol can improve blood sugar, triglyceride, and cholesterol levels in those with metabolic syndrome.
Supporting Mental Health: Inositol plays a crucial role in regulating neurotransmitters like serotonin and dopamine, which are key for mood balance. Research suggests it may help alleviate symptoms associated with panic disorder, obsessive-compulsive disorder (OCD), and, in some cases, depression. Some studies indicate that individuals with these conditions may have lower levels of inositol in their brains.
Enhancing Reproductive Health: In women with PCOS, inositol can be particularly effective. It has been shown to improve insulin function, lower high androgen levels, reduce triglycerides, and improve ovarian function, leading to more regular menstrual cycles and increased fertility. A specific ratio of myo-inositol to D-chiro-inositol (MI:DCI) has shown promise in managing PCOS symptoms.

Dietary Sources and Supplementation

Inositol is found naturally in a variety of foods, with some of the best sources including:

Fruits: Oranges, grapefruit, and cantaloupe are particularly good sources.
Grains: Whole grains and high-bran cereals, as well as brown rice, contain inositol.
Beans and Nuts: Legumes like beans and chickpeas, along with nuts like almonds, provide a healthy dose.
Organ Meats: Liver is a rich animal source.

While a healthy diet provides a small amount, therapeutic effects often require the higher concentrations found in supplements. Supplementation can be especially helpful for individuals with insulin resistance or other conditions where dietary intake may not be enough to produce a noticeable clinical effect. For specific conditions like PCOS, supplements often provide a targeted blend of myo-inositol and D-chiro-inositol.

Safety and Side Effects

Inositol is generally considered safe and well-tolerated by most people, especially at typical doses. Mild gastrointestinal side effects are the most commonly reported, particularly at higher doses, and may include nausea, gas, or diarrhea. In rare cases, higher doses have been reported to cause headaches, fatigue, or dizziness.

Precautions: Individuals with bipolar disorder should exercise caution, as very high doses might potentially trigger manic episodes. Pregnant and lactating women should consult a healthcare provider before taking supplements, although some studies have investigated myo-inositol for gestational diabetes. It is always important to discuss new supplements with a doctor, especially when managing existing health conditions or taking other medications.

Conclusion

In summary, while inositol was once mistakenly classified as a B vitamin, it is not one in the traditional sense because the body can produce it. Instead, this powerful pseudovitamin plays a crucial role in various metabolic and neurological functions, influencing everything from insulin sensitivity to mood regulation. Though a healthy diet provides natural sources, supplements are often utilized for their therapeutic potential in managing specific conditions like PCOS and metabolic syndrome. Always consult a healthcare professional to determine if inositol supplementation is right for you, especially concerning dosage and potential interactions with other medications.

This article is for informational purposes only and does not constitute medical advice. For specific health concerns, consult a qualified healthcare provider. (Learn more about inositol research on the NIH website)

Frequently Asked Questions

No, inositol is not officially a B vitamin, though it was once referred to as Vitamin B8. This classification was changed after it was discovered that the human body can produce its own supply.

Inositol was reclassified as a pseudovitamin because it is not an essential nutrient that must be consumed through the diet. The kidneys and liver can synthesize it from glucose, so the body can produce its own supply.

Myo-inositol (MI) and D-chiro-inositol (DCI) are different forms (isomers) of inositol. MI is the most abundant form and primarily helps with cellular glucose uptake, while DCI assists with glycogen synthesis. The optimal balance of these two is important, especially for women with PCOS.

Inositol offers several potential health benefits, including improving insulin sensitivity, supporting mental health (for anxiety, panic disorder, and OCD), and enhancing female reproductive health, particularly in women with PCOS.

You can find inositol in various foods such as citrus fruits, beans, whole grains, nuts, and organ meats. Some specific examples include grapefruit, cantaloupe, wheat bran, and liver.

Inositol is generally well-tolerated, but common side effects can include mild gastrointestinal discomfort like nausea, gas, and diarrhea, especially at higher doses. Other less common side effects may include headaches and dizziness.

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