Inositol is a sugar-like alcohol (sugar alcohol) that occurs in nine stereoisomers. In dietary supplements, myo-inositol and D-chiro-inositol are the most relevant, often combined in a 40:1 ratio. Because the body produces inositol itself, it isn't a true vitamin; it's also found in many foods.
Inositol is a sugar-like alcohol that occurs in nine different forms – in supplementation, myo-inositol and D-chiro-inositol are the most relevant, often combined in a 40:1 ratio. Inositol used to be occasionally referred to as "vitamin B8", but strictly speaking it is not a vitamin, because the body can produce it itself. In this guide you will learn, factually and neutrally, what inositol is chemically, how the two main forms differ, which foods contain it and what to look out for in supplements.
The key points in brief
- Inositol is a sugar alcohol and occurs in nine stereoisomers.
- By far the most common natural form is myo-inositol.
- Another well-known variant is D-chiro-inositol, often combined with myo-inositol in a 40:1 ratio.
- The body produces inositol itself; in addition, it occurs in many foods.
- For inositol there are currently no approved health claims in the EU – we describe it neutrally.
What is inositol – and why is it not a true vitamin?
Chemically, inositol belongs to the sugar alcohols. Despite the name, it has nothing to do with the alcohol you drink: it is a ring-shaped compound with six carbon atoms bearing hydroxyl groups. This structure resembles that of grape sugar (glucose), which is why inositol tastes slightly sweet. The decisive point: the body can synthesise inositol itself, among other things from glucose. Because it does not depend on being supplied from outside, inositol is not considered an essential nutrient and therefore not a true vitamin either. The former designation "vitamin B8" is a historical relic and is outdated today.
There are a total of nine so-called stereoisomers – variants with the same molecular formula but a different spatial arrangement of the atoms. In supplementation practice, two of them are particularly relevant.
What inositol is in the body
Inositol is more than just a sweet-tasting sugar alcohol – it is a building block of cell structures. In cell membranes it occurs in bound form as a component of certain fat compounds (phosphatidylinositols). These are part of the cell's own signalling system: information is relayed within the cell via them. This is well-characterised cell biology and textbook knowledge – and the reason why inositol is scientifically interesting. From this role, however, we do not derive any specific health benefit for a supplement; more on that below.
Myo-inositol and D-chiro-inositol: the difference
| Form | Occurrence | Distinctive feature |
|---|---|---|
| Myo-inositol | most common natural form | base form from which others can arise |
| D-chiro-inositol | rarer; formed in the body from myo-inositol | often contained in combination products |
Myo-inositol is the dominant form in the body and in food. D-chiro-inositol occurs more rarely and can be converted in the body from myo-inositol by an enzyme. Many products combine the two in a fixed quantity ratio. A frequently cited ratio is 40:1 (myo- to D-chiro-inositol), modelled on the estimated natural ratio in certain body fluids. This is a pure description of the product composition and not a statement about any health effect.
What research is investigating
Well established and textbook knowledge is the biochemistry: inositol is an endogenous sugar alcohol and a building block of certain cell structures, among other things in cell membranes and in the cells' signalling system. Beyond that, the roles of myo- and D-chiro-inositol in metabolism are actively being researched, as is the question of which ratio of the two forms in the body and in supplements makes sense. Much of this is the subject of ongoing investigations; there are as yet no claims derived from it that are approved for foods in the EU. We therefore stick to what can be described with certainty – chemistry, forms, occurrence and use.
Natural sources in food
Inositol is present in many plant and animal foods and is part of a normal diet. Good sources are:
- citrus fruits (especially the fruit membranes and the white part under the peel)
- legumes such as beans, chickpeas and lentils
- wholegrain cereals and bran
- nuts and seeds
In plant foods, inositol is often present in bound form as phytic acid (inositol hexaphosphate). Through a plant-based diet, people therefore regularly take in inositol – together with the body's own production, the organism is thus generally well supplied. Typical daily intake from food is in the range of around one gram, but can vary considerably depending on eating habits. Anyone who eats a lot of wholegrains, legumes and fruit tends to take in more than with a heavily processed diet.
Forms and use in supplementation
In supplements, inositol is usually offered as a slightly sweet powder or in capsules. Thanks to good water solubility, the powder dissolves easily and can be stirred into water, juice or other drinks – many find the slight sweetness pleasant. Because inositol is water-soluble, intake is flexible; a fixed time is not prescribed. In addition to myo- and D-chiro-inositol, combination products sometimes contain further substances such as folic acid or certain vitamins. Powder offers freely selectable dosing, capsules are practical for on the go. On the fundamental question of absorption, it is worth taking a look at Bioavailability simply explained; for dosing powder, Dosing powder correctly helps.
What you can look out for in terms of quality
- Form and ratio: a clear indication of myo- and, where applicable, D-chiro-inositol, including the quantity ratio.
- Purity: ideally without unnecessary additives, sweeteners or flavourings; laboratory-tested (see Laboratory-tested: what does that mean?).
- Declared amount: the stated content per daily portion.
- Dosage form: powder for flexible dosing, capsules for on the go.
As a German manufacturer with laboratory testing, Scheunengut relies on clean raw materials and traceable declaration.
Honestly put into context
What is established is what inositol is chemically, that the body produces it itself and where it occurs in food. What is open – or legally not usable as a claim – are specific health effects: for inositol there are currently no approved health claims in the EU under Regulation (EU) No 432/2012. We therefore describe it factually and neutrally. For health-related questions or persistent complaints – and generally during pregnancy, breastfeeding or when taking medication – please consult your doctor.
Suitable products & further guides
You will find inositol and related vital substances in the overview under Vitamins, Minerals & Trace Elements. Since inositol was historically assigned to the B vitamins, the category B Vitamins also fits. For further reading: B vitamins at a glance (B1–B12), Choline, Which supplement suits your goal, Bioavailability simply explained and Nutrients for women.
Frequently asked questions (FAQ)
Is inositol a vitamin?
No, strictly speaking not. Inositol used to be occasionally referred to as vitamin B8, but it is a sugar alcohol that the body can produce itself – among other things from glucose. Because it does not depend on being supplied from outside, inositol is not considered an essential nutrient.
What does the 40:1 ratio for inositol mean?
It describes the quantity ratio of myo-inositol to D-chiro-inositol in many combination supplements. The 40:1 ratio is modelled on the estimated natural ratio in certain body fluids. It is a pure statement about the product composition and not a claim about any effect.
Which foods contain inositol?
In citrus fruits (especially in the fruit membranes), legumes such as beans, chickpeas and lentils, in wholegrain cereals and bran, and in nuts and seeds. In plant foods it is often present in bound form as phytic acid.
As a powder or capsule – which form is better?
Both have advantages. Powder dissolves well in drinks and allows a freely selectable dose, capsules are practical for on the go. Since inositol is water-soluble, intake is flexible in terms of timing. The choice is above all a question of handling and preference.
Health notice: This guide is for general information purposes only and does not replace individual medical or pharmaceutical advice. Food supplements are not a substitute for a balanced, varied diet and a healthy lifestyle. If you have health concerns, are pregnant or breastfeeding, or are taking medication, please consult a doctor or pharmacist. How our guides are created →
Sources
- Dietary Supplements – Yes or No — Verbraucherzentrale
- Health assessment of food supplements — German Federal Institute for Risk Assessment (BfR)
- Colorful Pills for a Clear Conscience – What Do Dietary Supplements Actually Do? — German Nutrition Society (DGE)
- Food supplements — European Food Safety Authority (EFSA)
