Cinnamon for Blood Sugar
Cinnamon is the most-recommended and least-settled entry in this section. It is the spice people reach for first and the one with the weakest case, and there is a second problem underneath the efficacy question that matters more: the common supermarket species carries a liver toxin the expensive one does not.
Evidence tier 2: positive trials exist, and the most careful review of them concluded the evidence does not support the use.
Table of Contents
What the Review Actually Concluded
Costello and colleagues wrote a narrative review for the Journal of the Academy of Nutrition and Dietetics in 2016 asking directly whether cinnamon supplements have a role in glycemic control in type 2 diabetes. Their answer was that the evidence is insufficient to support it.
That conclusion is worth sitting with, because it is not the same as "cinnamon does nothing." Individual trials have reported reductions in fasting glucose. The problem is that the trials disagree with each other, use different species and doses, and the better-controlled ones tend to show less. When a literature looks like that, the honest summary is that the effect — if there is one — is small enough to be swamped by study design.
Cinnamon is also the clearest example on this site of a supplement whose reputation runs well ahead of its data. It is cheap, pleasant and nearly universally recommended, and none of those are evidence.
Cassia versus Ceylon: The Coumarin Problem
This is the part to act on regardless of what you conclude about glucose.
Most cinnamon sold in supermarkets and in supplements is cassia (Cinnamomum cassia), and cassia contains coumarin, a compound with documented hepatotoxicity in susceptible people. Ceylon cinnamon (Cinnamomum verum, sometimes called "true cinnamon") contains only trace amounts.
The doses used in glucose experiments — grams per day, sustained — are exactly the doses at which cassia coumarin intake becomes a real consideration, which is an uncomfortable combination: the amount you would take to chase an unproven benefit is the amount at which a known risk starts to matter. If you take cinnamon daily, take Ceylon. The cassia vs Ceylon and coumarin page covers the numbers.
If You Take It Anyway
Culinary quantities of cinnamon on food are not what this page is about and are not a concern. The considerations here apply to daily supplemental dosing:
- Use Ceylon, and check that the label says so — "cinnamon" without a species means cassia.
- Do not treat it as a substitute for anything that works. It is an addition at best.
- Give it a defined trial. If you are going to take it, measure before and after rather than taking it indefinitely on faith.
Cautions
- It lowers blood glucose, and so does your medication. The effects add. With insulin or a sulfonylurea this is a hypoglycemia risk, and dose changes belong with the prescriber — see hypoglycemia awareness and prevention.
- Cassia cinnamon carries a hepatotoxic coumarin load. At supplemental doses this is the main safety issue, and it is avoidable by using Ceylon.
- Caution with existing liver disease or with other hepatotoxic medications.
- Measure, do not assume. Adding a supplement without measuring means you learn about an interaction from a symptom rather than from a number.
Key Research Papers
Every DOI below was checked against Crossref and the abstract read for support before it was listed.
- Costello RB, Dwyer JT, Saldanha L, et al. Do Cinnamon Supplements Have a Role in Glycemic Control in Type 2 Diabetes? A Narrative Review. Journal of the Academy of Nutrition and Dietetics, 2016;116(11):1794–1802.