Inositol: The Unofficial 'B8 Vitamin' with Strong Clinical Evidence
Inositol is sometimes called vitamin B8, though that designation is unofficial — the body can synthesise it from glucose. However, therapeutic doses used in clinical research far exceed the body's production capacity, which is why supplementation has real clinical value.
Inositol has an impressive evidence base for polycystic ovary syndrome (PCOS), anxiety disorders, insulin sensitivity, and metabolic health — making it one of the most underrated water-soluble supplements available.
The Inositol Family
Inositol exists as nine structural isomers. The two with the greatest clinical relevance are:
Myo-Inositol (MI)
The most abundant form in the body. Participates in insulin signalling, phosphoinositide second messenger systems, and serotonin receptor modulation (Croze & Soulage, 2013).
D-Chiro-Inositol (DCI)
A mediator of insulin action derived from myo-inositol. Critical for glucose uptake in skeletal muscle. Women with PCOS show a tissue-specific deficiency of DCI (Bevilacqua et al., 2015).
The 40:1 Ratio (MI:DCI)
The physiological ratio found in healthy tissues — and the combination showing the strongest results in PCOS clinical research.
Clinical Evidence Summary
PCOS (Polycystic Ovary Syndrome)
PCOS is the most studied inositol application. Myo-inositol (2–4 g/day) has demonstrated:
- Normalisation of LH/FSH ratio
- Restored ovulation in anovulatory women
- Reduced androgen levels (testosterone, DHEA-S)
- Improved insulin sensitivity
- Higher pregnancy rates in fertility treatment
A meta-analysis (Unfer et al., 2017) confirmed efficacy of 4 g myo-inositol + 400 mcg folate versus folate alone.
Anxiety and OCD
Inositol modulates serotonin and other neurotransmitter signalling in the brain. Studies have found:
- 18 g/day significantly reduced panic attack frequency (Benjamin et al., 1995)
- OCD symptom severity reductions comparable to fluoxetine in some studies
- Mild antidepressant effects at high doses
Note: these are very high doses — standard 2–4 g supplements may not achieve anxiety effects.
Insulin Sensitivity and Pre-Diabetes
Myo-inositol improves insulin receptor sensitivity through a mechanism similar to, but milder than, metformin. Research in high-risk women shows improved glucose tolerance (Croze & Soulage, 2013). A broader review of how inositol isomers interact with insulin signalling is available in Bevilacqua & Bizzarri (2018).
OstroVit Inositol 200g Naturaalne (€16.90 at the time of writing) provides inositol in flexible powder form for precise dosing, available at maxfit.ee.
NOW Inositol 500mg 100caps (€14.90 at the time of writing) is a convenient capsule format for daily maintenance use.
Inositol for Athletes
For athletic populations, inositol offers:
- Glucose metabolism optimisation — improves carbohydrate utilisation efficiency
- Serotonergic support — potential mood and recovery benefits during heavy training
- Cell membrane phospholipid synthesis — structural role in cell health
Safety and Side Effects
Inositol is well-tolerated at standard doses. At very high doses (above 12 g/day), some people experience:
- Nausea
- Loose stools
- Headache
Start with 1–2 g and titrate up gradually. Most people tolerate 4 g/day without issues.
Dosing Guide
- PCOS and insulin sensitivity: 2–4 g myo-inositol/day, ideally combined with DCI at 40:1 ratio
- Anxiety protocols (research doses): up to 18 g/day — only with specialist guidance
- General health and metabolic support: 1–2 g/day
- Take in split doses with meals for best tolerance
FAQ
Which inositol is best for PCOS?
The combination of myo-inositol and D-chiro-inositol at a 40:1 ratio has the strongest clinical evidence for PCOS. 4 g myo-inositol with 100 mg D-chiro-inositol daily is the most commonly studied dose.
Can inositol help with anxiety?
Clinical studies used very high doses (12–18 g/day) to show anxiolytic effects. A standard 2–4 g supplement may not replicate these results. It can be used as a supportive measure but should not replace clinical treatment for anxiety disorders.
Is inositol found in food?
Yes — in citrus fruits, beans, whole grains, and nuts. However, dietary amounts are far below the therapeutic doses used in research. For clinical outcomes in PCOS or metabolic health, supplementation is necessary.
References
- Croze, M. L., & Soulage, C. O. (2013). Potential role and therapeutic interests of myo-inositol in metabolic diseases. Biochimie, 95(10), 1811–1827. https://pubmed.ncbi.nlm.nih.gov/23764390/
- Unfer, V., Facchinetti, F., Orrù, B., Giordani, B., & Nestler, J. (2017). Myo-inositol effects in women with PCOS: a meta-analysis of randomized controlled trials. Endocrine Connections, 6(8), 647–658. https://pubmed.ncbi.nlm.nih.gov/29042448/
- Benjamin, J., Levine, J., Fux, M., Aviv, A., Levy, D., & Belmaker, R. H. (1995). Double-blind, placebo-controlled, crossover trial of inositol treatment for panic disorder. American Journal of Psychiatry, 152(7), 1084–1086. https://pubmed.ncbi.nlm.nih.gov/7793450/
- Bevilacqua, A., Carlomagno, G., Gerli, S., et al. (2015). Results from the International Consensus Conference on myo-inositol and D-chiro-inositol in Obstetrics and Gynecology—assisted reproduction technology. Gynecological Endocrinology, 31(6), 441–446. https://pubmed.ncbi.nlm.nih.gov/26036719/
- Bevilacqua, A., & Bizzarri, M. (2018). Inositols in insulin signaling and glucose metabolism. International Journal of Endocrinology, 2018, 1968450. https://pubmed.ncbi.nlm.nih.gov/30595691/
Also read our guide to inositol timing and overview of inositol deficiency signs. See also:
- Myo-inositol for PCOS: 2026 guidelines update
- Women's health products
- Vitamin complexes
