Cinnamon: repeatedly meta-analysed, with results that genuinely conflict — a 2013 review found improvements, a 2016 narrative review pushed back, and more recent dose-response work found effects again. Real signal, small effect, unresolved. Chromium: better-behaved evidence for people with type 2 diabetes and modest effects; much weaker justification for everyone else. Neither is a treatment.
Cinnamon: the ingredient the meta-analyses can't agree on
Cinnamon is unusual in this field because it has been studied enough to be reviewed and re-reviewed — and the reviews disagree with each other. That's frustrating if you want an answer, and genuinely informative if you want the truth.
2013: a positive meta-analysis
Allen and colleagues pooled randomised controlled trials in type 2 diabetes and reported improvements in fasting glucose and lipid measures.1 This is the paper that a decade of supplement marketing has been citing, usually without the caveats its authors included.
2016: the pushback
Costello and colleagues published a narrative review asking, essentially, whether cinnamon supplements have any real role in glycaemic control — and reached a considerably more sceptical conclusion, pointing at heterogeneity in the trials, differences in preparation, and inconsistency in outcomes.2
Note what happened there: same ingredient, largely overlapping literature, opposite emphasis. When that occurs, it almost always means the true effect is small enough that methodological choices can flip the conclusion.
2024–2025: dose-response, and effects again
Moridpour and colleagues ran an updated systematic review with dose-response meta-analysis in type 2 diabetes and found effects on glycaemic control,3 and a 2025 systematic review and meta-analysis looked at metabolic biomarkers more broadly and also found signal.4
The dose-response element matters more than the headline. A dose-response relationship — more ingredient, more effect — is one of the classic markers that an effect is real rather than noise. It's the strongest thing cinnamon has going for it.
The species problem — cassia vs. Ceylon
This is the part almost no product page mentions, and it's the practically useful one.
Most cinnamon sold in the world, and most cinnamon in supplements, is Cinnamomum cassia. It's cheaper than Ceylon cinnamon (C. verum), and it contains substantially more coumarin — a compound with recognised liver toxicity concerns at high, sustained intakes.
For a sprinkle on porridge, this is a non-issue. For someone taking a concentrated cassia extract every day for a year, it stops being a non-issue and becomes something worth knowing about. If a label says only “cinnamon bark,” assume cassia; if a manufacturer uses Ceylon, they say so, because it costs more.
| Cassia | Ceylon | |
|---|---|---|
| What you get by default | Almost always this — in supermarkets and supplements alike | Only when explicitly stated and paid for |
| Coumarin content | Substantially higher | Very low |
| Most trial evidence | Mostly cassia | Less studied |
| Daily long-term use | Worth a conversation with a doctor | Lower concern |
Chromium: better evidence, narrower application
Chromium is an essential trace mineral involved in insulin signalling. The deficiency case is straightforward — if you're low, correcting it helps. The interesting question is whether supplementing someone who isn't deficient does anything.
Asbaghi and colleagues examined chromium supplementation and glycaemic control specifically in people with type 2 diabetes and found effects,5 and earlier work looked at both diabetes and high-risk populations.6 There's also a reasonable background literature on micronutrient status in type 2 diabetes suggesting that deficiencies in this group are more common than in the general population,7 which gives the whole idea a plausible foundation.
So: reasonable evidence in diagnosed type 2 diabetes, thinner evidence in people who simply spike after lunch, and an effect size that is modest wherever it appears.
The dose question, which is where products differ most
Chromium doses in supplements vary by an order of magnitude, and this is one of the few places where you can actually compare products meaningfully because chromium is a mineral and therefore almost always disclosed individually rather than buried in a blend.
- Around 200 mcg is the common low-end dose. It's cheap and it lets a label say “contains chromium.”
- Around 1,000 mcg (1 mg) is closer to the range used in the trials. Gluco6, for instance, uses 1 mg as chromium niacinate — five times the common dose, and one of the genuinely defensible things about that product.
Which raises the obvious point: when a product does disclose a dose, you can judge it. When it hides the dose in a blend, you can't. That asymmetry is the whole argument of the buying checklist.
How this plays out on a real label
Gluco6 is a useful case study for both ingredients: chromium at a generous, disclosed 1 mg, and cassia cinnamon hidden inside a 525 mg proprietary blend where its dose is anyone's guess. Same product, best and worst practice side by side.
Disclosure: that review contains affiliate links. It scores the product 3.4 out of 5.
Safety notes worth taking seriously
Both of these can interact with medication. Chromium and cinnamon are studied because they may affect blood glucose; combining either with metformin, insulin or another glucose-lowering drug can have an additive effect. Talk to your prescriber first. Full walkthrough here.
Cassia cinnamon and the liver. If you have liver disease, drink heavily, or take a medication with hepatic considerations, high-dose daily cassia extract is worth raising with a doctor because of coumarin.
Chromium and the kidneys. People with kidney disease should not supplement chromium without medical advice.
What I'd actually conclude
Cinnamon has a small, contested, possibly real effect on fasting glucose, mostly demonstrated in people with type 2 diabetes, and comes with a species question most labels don't answer. Not a reason to buy a product; not a reason to be annoyed it's included either.
Chromium has the more coherent evidence base of the two, and it's the ingredient where dose most clearly separates a serious formula from a decorative one. If a blood sugar product uses 200 mcg, someone was ticking a box.
And both sit at position seven on the list of levers that actually move your glucose, well behind what you eat, in what order, and whether you move afterwards.
References
- Allen RW, et al. Cinnamon use in type 2 diabetes: an updated systematic review and meta-analysis. Ann Fam Med. 2013. PMID 24019277
- Costello RB, et al. Do Cinnamon Supplements Have a Role in Glycemic Control in Type 2 Diabetes? A Narrative Review. J Acad Nutr Diet. 2016. PMID 27618575
- Moridpour AH, et al. The effect of cinnamon supplementation on glycemic control in patients with type 2 diabetes mellitus: an updated systematic review and dose-response meta-analysis of randomized controlled trials. Phytother Res. 2024. PMID 37818728
- de Moura SL, et al. Effects of cinnamon supplementation on metabolic biomarkers in individuals with type 2 diabetes: a systematic review and meta-analysis. Nutr Rev. 2025. PMID 38917435
- Asbaghi O, et al. Effects of chromium supplementation on glycemic control in patients with type 2 diabetes. Pharmacol Res. 2020. PMID 32730903
- San Mauro-Martin I, et al. Chromium supplementation in patients with type 2 diabetes and high risk of type 2 diabetes. Nutr Hosp. 2016. PMID 27019254
- Kaur B, et al. Micronutrient status in type 2 diabetes: a review. Adv Food Nutr Res. 2014. PMID 24484939
Medical disclaimer. General information written by a layperson, not medical advice. Nothing here diagnoses, treats, cures or prevents any disease. Talk to a qualified healthcare professional before starting any supplement, particularly if you take medication or have liver or kidney disease.