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Supplements to Lower Blood Sugar: Berberine, Fiber, Cinnamon and What to Know With Diabetes

In type 2 diabetes and prediabetes, a few supplements lower blood sugar a little on top of diet, exercise and medicines. Berberine and soluble fiber such as psyllium each lowered HbA1c by about 0.6 points in pooled trials (grade B); cinnamon, magnesium and vitamin D results are mixed. Berberine is not a natural substitute for GLP-1 drugs. If you use insulin or other diabetes medicines, adding a supplement can push blood sugar too low.

Published How we grade evidenceEditorial policy

This guide is mainly about type 2 diabetes and prediabetes in adults; type 1 and gestational diabetes have their own short sections. HbA1c is a blood test of average blood sugar over about 3 months.

The short version

  • Lifestyle came first in the key trial: in adults at high risk, a diet and exercise program cut new diabetes by 58%, more than metformin (31%) (Knowler 2002).
  • Berberine lowered HbA1c by 0.63 points across 37 studies, often alongside diabetes pills. Grade B (Xie 2022).
  • Soluble fiber lowered HbA1c by 0.63 points across 29 trials. Grade B (Xie 2021).
  • Cinnamon helped in newer pooled trials but not in a Cochrane review. Grade C, mixed (de Moura 2025; Leach 2012).
  • Vitamin D slightly lowered the chance of prediabetes turning into diabetes in pooled trials. Grade B (Pittas 2023).
SupplementWhat trials foundSize of effectGrade
BerberineLower HbA1c and fasting glucoseHbA1c 0.63 points lowerB
Soluble fiber, psylliumLower HbA1c and fasting glucoseHbA1c 0.63 points lowerB
CinnamonReviews disagreeHbA1c 0.56 lower in one pooling, none in anotherC
MagnesiumSmall fasting glucose drop, HbA1c unclearSmallB
Vitamin D (prediabetes)Slightly fewer new cases of diabetes3.3% fewer over 3 yearsB
ChromiumResults vary hugelyUnclearC
Apple cider vinegarSmall trials, harms to teethUnclearC

What lowers blood sugar the most?

Not supplements. In the Diabetes Prevention Program, adults at high risk who joined a lifestyle program cut their rate of new diabetes by 58% against placebo, and metformin cut it by 31% (Knowler 2002). For diagnosed type 2 diabetes, medicines such as metformin and GLP-1 drugs have the strongest evidence; your prescriber sets them. Supplements are at most small add-ons. See our type 2 diabetes findings, prediabetes findings and type 2 diabetes protocol.

Does berberine lower blood sugar?

Grade B. Pooling 37 studies in type 2 diabetes (3,048 people), HbA1c fell 0.63 points and fasting glucose 0.82 mmol/L on berberine, more when starting levels were high; many trials added it to diabetes pills (Xie 2022). A larger 2024 pooling found most trials used 0.9 to 1.5 g a day for 1 to 3 months (Wang 2024). Of 54 reviews of berberine, 45 were rated very low quality, so the size of the effect is uncertain (Shi 2025). See our berberine page.

Berberine changes how drugs are cleared. In healthy men it slowed three liver enzymes, lifting blood levels of a test drug by 40% (Guo 2012), and in one of two small tests in healthy men it pushed up cyclosporine, a transplant drug, by about a fifth (Xin 2006). If you take metformin, read can I take berberine with metformin? and ask your prescriber.

Is berberine "nature's Ozempic"?

No. Across 23 trials, berberine lowered weight by 0.88 kg (Elahi Vahed 2026). In a 68-week trial in adults with overweight or obesity, weekly semaglutide injections cut weight by 14.9% against 2.4% on placebo (Wilding 2021). We found no trial comparing the two directly. If you take a GLP-1 drug, see supplements on GLP-1 medicines; for weight, see weight-loss supplements.

Do fiber supplements lower blood sugar?

Grade B. Pooling 29 trials (1,517 people with type 2 diabetes), soluble fiber supplements lowered HbA1c by 0.63 points and fasting glucose by 0.89 mmol/L, though results varied between trials (Xie 2021). With psyllium taken before meals, the drop was largest in people already treated for type 2 diabetes and absent in people with normal blood sugar (Gibb 2015). Take it with plenty of water and away from other medicines. See our psyllium and fiber pages.

Does cinnamon lower blood sugar?

Grade C, mixed. A 2012 Cochrane review of 10 trials (577 people with either type of diabetes) found no clear change in HbA1c and an inconclusive effect on fasting glucose (Leach 2012). A 2025 pooling of 28 trials (3,054 people with type 2 diabetes) found HbA1c 0.56 lower and fasting glucose 15.26 mg/dL lower, but results varied widely between trials (de Moura 2025). Most trials used cassia cinnamon (Leach 2012), which contains coumarin; coumarin can harm the liver in sensitive people, and heavy cassia users can reach the tolerable daily intake (Abraham 2010). Our type 2 diabetes page rates cinnamon B for a small improvement; we give it C because these two reviews disagree. See our cinnamon page.

Do chromium or apple cider vinegar help?

  • Chromium: grade C. Pooling 28 studies found fasting glucose 19 mg/dL lower and HbA1c 0.71 lower, but trials disagreed enormously (Asbaghi 2020); a reanalysis of 16 trials that allowed for placebo changes found no effect on fasting glucose (Bailey 2014). See our chromium page.
  • Apple cider vinegar: grade C. In 7 small studies in type 2 diabetes, it lowered fasting glucose by 21.9 mg/dL (Arjmandfard 2025). Drinking vinegar twice a day for 8 weeks raised tooth-wear scores by 18% (Anderson 2021), and a throat injury from a vinegar tablet led testers to find products that varied widely and may not have contained vinegar at all (Hill 2005).

Does magnesium help blood sugar?

Grade B, mixed. Pooling 23 trials (1,345 people with type 2 diabetes), magnesium lowered fasting glucose a little, with almost no change in HbA1c (Maqrashi 2025). In 5 prediabetes trials (384 people), fasting glucose did not change significantly, though 2-hour glucose fell (Basit 2026). Upper limit for adults: 350 mg of magnesium a day from supplements, because more can cause diarrhea; take more only with blood tests or your clinician's advice (NIH ODS; check your stack). With kidney disease, ask first, because magnesium can build up to harmful levels when the kidneys clear it poorly. See our magnesium page.

Does vitamin D help prediabetes?

Grade B for a small effect. In the D2d trial, 2,423 adults with prediabetes took 4,000 IU of vitamin D3 a day or placebo for a median of 2.5 years; 293 against 323 developed diabetes, a difference that was not statistically significant (Pittas 2019). Pooling D2d with two other prediabetes trials, one of which used a prescription vitamin D drug, cut the risk of diabetes by 15%, or 3.3 fewer cases per 100 people over 3 years (Pittas 2023). In 22,220 older adults not selected for prediabetes, 2,000 IU a day made no clear difference (Tobias 2025). Upper limit for adults: 4,000 IU (100 mcg) of vitamin D a day, because more can cause high blood calcium; take more only with blood tests or your clinician's advice (NIH ODS; check your stack). See our vitamin D page.

  • Inositol is studied mostly in PCOS; see supplements for PCOS.
  • Curcumin: grade B. Across 34 trials in prediabetes and type 2 diabetes, HbA1c fell 0.32 points (Bahari 2026). Some turmeric products have been linked to several dozen cases of acute liver injury (LiverTox); see supplements and your liver and our curcumin page.
  • Probiotics: grade C. HbA1c fell 0.44 points across 32 trials, but the reviewers rated the evidence low quality (Hejazi 2024). See our probiotics page.
  • Black seed: grade B. In 16 trials in type 2 diabetes, fasting glucose fell 21.43 mg/dL and HbA1c 0.44 points (Karimi 2025). Results varied widely between trials in a 30-trial pooling (Shirvani 2024).
  • Fenugreek: grade B. In 10 trials (706 people with type 2 diabetes or prediabetes), it lowered fasting glucose and HbA1c, with mild stomach upset (Kim 2023).
  • Gymnema: grade C. It lowered fasting blood sugar in 6 trials that the authors judged low quality (Zamani 2023).
  • Bitter melon: grade C. Cochrane found no clear effect in 4 trials (Ooi 2012); a later pooling of 10 trials found HbA1c 0.26 lower, on low to very low quality evidence (Peter 2019).
  • Alpha-lipoic acid: grade C. Sold for diabetic nerve pain, it probably made little or no difference to symptoms in a Cochrane review (Baicus 2024), and it can trigger insulin autoimmune syndrome, with repeated low blood sugar (Vallianou 2026).

What about type 1 diabetes?

No supplement replaces insulin. Our do vitamins help type 1 diabetes? page covers vitamin D and the rest. Supplements that lower glucose can change insulin needs: in a 1990 study of 27 people with type 1 diabetes, a gymnema leaf extract lowered insulin requirements in a small study that was not randomized, grade D (Shanmugasundaram 1990). On insulin, any glucose-lowering supplement raises your risk of low blood sugar (hypoglycemia), so test more often and tell your diabetes team first. See our type 1 diabetes findings and protocol.

What about gestational diabetes?

  • Myo-inositol: grade C. A 2023 Cochrane review of 7 trials (1,319 women, 6 of the trials in Italy) found it may lower the chance of gestational diabetes (6 trials, 1,140 women: risk ratio 0.53), with certainty rated low to very low (Motuhifonua 2023). As a treatment for diagnosed gestational diabetes, it has only 2 small trials (142 women) (Brown 2016).
  • Probiotics: grade A for harm, so we'd skip them. Their effect on gestational diabetes was uncertain, and they made pre-eclampsia more likely (risk ratio 1.85, high certainty) (Davidson 2021).
  • Vitamin D: grade C. The effect on gestational diabetes is very uncertain (Palacios 2024).

Take any supplement in pregnancy only as advised by your midwife or obstetric team. Avoid berberine in pregnancy: it displaced bilirubin from the blood protein that carries it, in lab and rat studies, and a berberine herb has been reported to raise the chance of jaundice-related brain damage (kernicterus) in newborns (Chan 1993). See our gestational diabetes findings, protocol and prenatal supplements guide.

What we'd skip

  • Berberine in pregnancy or around newborns, because it may worsen newborn jaundice (Chan 1993).
  • Probiotics to ward off gestational diabetes: more pre-eclampsia (Davidson 2021).
  • Bitter melon: no clear benefit in Cochrane's trials (Ooi 2012).
  • Apple cider vinegar tablets: throat injury and unreliable contents (Hill 2005).
  • Large daily amounts of cassia cinnamon: coumarin and the liver (Abraham 2010).

Safety and interactions

When to see a doctor

  • Emergency: vomiting, belly pain, fruity breath, fast breathing or confusion, which can mean diabetic ketoacidosis, especially in type 1.
  • Same day: very high readings with thirst, passing a lot of urine or weight loss; or shaking, sweating or confusion from low blood sugar after adding a supplement.
  • Before starting: pregnancy, kidney or liver disease, or any diabetes medicine.

Never stop insulin or metformin on your own; ask the prescriber or pharmacist. If you are under 18, ask a clinician.

FAQ

What supplement lowers blood sugar the most? Berberine and soluble fiber such as psyllium each lowered HbA1c by about 0.63 points in pooled trials in type 2 diabetes (grade B). Both are small next to lifestyle change and medicines.

Is berberine "nature's Ozempic"? No. It lowered weight by 0.88 kg across 23 trials, while weekly semaglutide cut weight by 14.9% in a 68-week trial in adults with overweight or obesity. We found no trial comparing the two directly.

Does cinnamon lower blood sugar? Reviews disagree (grade C, mixed): a 2025 pooling found HbA1c 0.56 lower, while a 2012 Cochrane review found no clear change. Cassia cinnamon contains coumarin, which can harm the liver.

Does apple cider vinegar help type 2 diabetes? Seven small studies found lower fasting glucose (grade C), but drinking vinegar daily wore down tooth enamel in a trial.

Can I take supplements with type 1 diabetes? No supplement replaces insulin. Glucose-lowering supplements can lower your insulin needs and cause lows, so tell your diabetes team first.

Sources

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