Health Reference Library

Which supplements for blood sugar have evidence?

This entry is part of the Nutri Tailor Health Reference Library — cited research on supplements, nutrients and adjacent areas of health.

Summary

All of these sit behind weight, movement and fibre. Berberine at 500 mg two or three times daily lowered fasting glucose and HbA1c in pooled randomised trials, mostly Chinese and of mixed quality, and it interacts with many prescriptions and is not for pregnancy. Myo-inositol at 2 to 4 g daily has its real evidence in PCOS, improving cycle regularity and insulin measures. Cinnamon at 120 mg to 6 g a day lowered fasting glucose modestly across ten trials with no HbA1c effect, and Cochrane called the evidence insufficient. Chromium shows small, inconsistent effects, mostly where glucose is already raised, with 200 micrograms the usual trial dose. Anyone on glucose-lowering prescriptions checks first.

How it works

Each of these works at the margin of insulin signalling. Berberine activates the same cellular energy sensor, AMPK, that exercise and metformin act on, which reduces liver glucose output and improves uptake; it is a pharmacologically active alkaloid rather than a nutrient. Myo-inositol is a second messenger in the insulin pathway and its effect is clearest where that pathway is disrupted, as in PCOS. Cinnamon's polyphenols improve insulin receptor signalling in cells and slow gastric emptying, which explains a fasting glucose effect without a sustained HbA1c effect. Chromium is a genuine cofactor for insulin action at tiny amounts, and adding more helps only where there was a shortfall or where glucose is already high. None replaces the glucose sink that muscle provides or the liver-fat reduction that weight loss delivers.

Effective dose

Berberine trials used 500 mg two to three times daily with meals for 8 to 12 weeks or longer. Myo-inositol trials in PCOS used 2 g twice daily, sometimes combined with D-chiro-inositol in a 40 to 1 ratio, judged at three to six months, detailed on the [inositol dosage page](/apps/learn/inositol-dosage-and-timing-how-to-run-a-fair-test). Cinnamon trials ranged from 120 mg to 6 g a day over 4 to 18 weeks, with Ceylon cinnamon preferred for long-term use because cassia carries coumarin. Chromium trials mostly used 200 to 1,000 micrograms of chromium picolinate a day; UK adults need around 25 micrograms, set out on the [chromium picolinate page](/apps/learn/what-is-chromium-picolinate-and-does-it-help-blood-sugar).

Timing

HbA1c moves over three months, so every option here is judged at a three-month re-test, not on a finger-prick glucose reading. Berberine effects on fasting glucose appear within weeks. Inositol in PCOS is judged at three to six months. Chromium and cinnamon, where they do anything, show at three months.

Safety profile

Berberine interacts with many prescriptions through liver enzymes, can drop glucose too far alongside glucose-lowering prescriptions, is not taken in pregnancy or breastfeeding, and commonly causes digestive upset at trial doses. Cassia cinnamon at gram doses delivers coumarin that can affect the liver; Ceylon cinnamon carries far less. Chromium above 1,000 micrograms a day has no evidence of extra benefit and isolated reports of kidney and liver effects. Inositol is well tolerated, with loose stools at higher doses. Anyone on insulin or sulfonylureas must involve their clinician before adding any glucose-active supplement, because hypoglycaemia is the risk.

Special populations

For women with PCOS, inositol comes first by evidence. For people on metformin, berberine works on overlapping mechanisms and the combination needs a clinician. In pregnancy none of these applies except, under clinical guidance, inositol. For older adults on multiple prescriptions, berberine's interaction profile usually rules it out. People with kidney disease avoid high-dose chromium.

Guideline positions

NICE NG28 does not recommend any supplement for glucose management; diet, weight and movement come first. The berberine evidence is a 2015 meta-analysis of randomised trials in type 2 diabetes, hyperlipidaemia and hypertension concluding berberine had comparable effects to conventional therapy with no serious side effects, noting the trials were mostly Chinese and of variable quality. The 2023 international PCOS guideline includes inositol as an option, and a 2024 systematic review found myo-inositol improved menstrual regularity and insulin measures. For cinnamon, the 2013 pooled analysis of 10 trials found fasting glucose and lipid reductions but no significant HbA1c change, while the 2012 Cochrane review judged the evidence insufficient. The American Diabetes Association does not recommend chromium.

Practical framework

The first three levers are decided before any of these, on [how to lower blood sugar](/apps/learn/how-to-lower-blood-sugar-what-the-evidence-supports). Where HbA1c sits in the 42 to 47 zone and no glucose-lowering prescription is in place, berberine at trial dose for 12 weeks with an HbA1c retest is the option with the most evidence, accepting the quality caveats and the interaction rules. Where the underlying picture is PCOS, inositol is the evidence-based choice and berberine is not needed. Cinnamon is a kitchen-dose experiment rather than a therapy. Chromium suits people whose diet is poor or whose glucose is already raised, at 200 micrograms, judged at three months. Nutri365 reads whether any of these is moving HbA1c, against weight and movement changes made at the same time, checks for interactions and contraindications against anything prescribed, and refers questions outside scope to a health specialist.

Common misconceptions

A supplement cannot substitute for the 5 to 10 kg that moves HbA1c in trials. Cinnamon at kitchen doses is food rather than an intervention. Berberine is a drug-like compound rather than a harmless herb, which is exactly why it has measurable effects and measurable interactions. A lower finger-prick glucose reading on the day is not a lower HbA1c at three months.

Sources

  1. Lan J, Zhao Y, Dong F, et al 2015. Meta-analysis of the effect and safety of berberine in the treatment of type 2 diabetes mellitus, hyperlipemia and hypertension. Journal of Ethnopharmacology. PMID: 25498346
  2. Allen RW, Schwartzman E, Baker WL, Coleman CI, Phung OJ 2013. Cinnamon use in type 2 diabetes: an updated systematic review and meta-analysis. Annals of Family Medicine. PMID: 24019277 · DOI: 10.1370/afm.1517
  3. Leach MJ, Kumar S 2012. Cinnamon for diabetes mellitus. Cochrane Database of Systematic Reviews. PMID: 22972104 · DOI: 10.1002/14651858.CD007170.pub2
  4. Fitz V, Graca S, Mahalingaiah S, et al 2024. Inositol for Polycystic Ovary Syndrome: A Systematic Review and Meta-analysis to Inform the 2023 Update of the International Evidence-based PCOS Guidelines. Journal of Clinical Endocrinology and Metabolism. PMID: 38163998
  5. Teede HJ, Tay CT, Laven JJE, et al; International PCOS Network 2023. Recommendations from the 2023 international evidence-based guideline for the assessment and management of polycystic ovary syndrome. European Journal of Endocrinology. PMID: 37580861
  6. 2024. Chromium: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements.
  7. 2022. Type 2 diabetes in adults: management (NG28). NICE.

Related entries

Back to chromium overview