Cinnamon, for blood sugar regulation?

Yesterday a patient asked me about taking cinnamon to help with her uncontrolled diabetes. Other people, some with pre-diabetes and some just trying to optimize their blood glucose levels, have asked me the same. Turns out cinnamon is worth a quick review together. I personally went down all kinds of rabbit holes, festooned with bad studies and even worse influencing, as I tried to compose for her an excellent, evidence-based answer (and a post for everyone here).

So I’m going to spare you that deep dive,

and instead bring you the distilled bottom line

in this latest installment of my…

Maybe a little, but the evidence is pretty weak. A 2023 review of 28 trials in ~3K people found that cinnamon lowered fasting blood sugar and three month average blood sugars (HBA1c). But this oft-cited review was full of statistical landmines and red flags, and would have the casual reader believing that cinnamon was as effective as some prescription diabetes medications. In short, it’s a house of cards. It might have been what my patient read before seeing me, given her enthusiasm.

An earlier Cochrane review, the gold standard for this kind of analysis, looked at 10 trials and found no significant benefit for HbA1c, insulin, or glucose levels after meals. Most trials of cinnamon were found to have uncertain or high risk of bias to boot. Cochrane tries extra hard to weed out bad studies.

And this is absolutely true: unlike FDA-approved medications for diabetes, no study of cinnamon has shown prevention of heart attacks, kidney disease, or any other diabetes complication. Doubtful they even tried to look.

Cinnamon is not a substitute for prescribed diabetes medication. Never reduce, stop, or refuse medications in favor of a supplement here. And I would not count on meaningful reductions in blood sugar for folks with pre-diabetes, or health-conscious people trying to keep their blood glucose levels down.

Most cinnamon that we buy in supermarkets is cassia cinnamon, which contains coumarin. Coumarin is a compound that can damage the liver in high doses. It is not to be confused with the blood thinner coumadin (although it is biochemically related, it does not thin the blood).

A level teaspoon of cassia carries roughly 4.5 to 20 mg of coumarin depending on the brand and production methods.

The same teaspoon of Ceylon cinnamon carries under 1 mg.

European regulators set a safe daily limit of about 7 mg of coumarin for an adult. So a single teaspoon of cassia can meet or exceed a full day’s allowance.

I came across a number of reports of liver toxicity from too much cinnamon, including examples in this report from Australia. Most doctors do not think of cinnamon when we are trying to figure out why someone’s liver enzymes are showing damage/inflammation… but we do have a healthy distrust of most wild card supplements for reasons like this.

Our livers clear coumarin using the same enzymes used for many prescription drugs. When that machinery is already tied up with handling those meds (or ample doses of cassia cinnamon), the coumarin clearance takes a different metabolic pathway and produces by-products that can be toxic to the liver. For example, one case report involved acute hepatitis in a person taking a cinnamon supplement with their prescribed rosuvastatin (Crestor, for high cholesterol). There are genetic variants of these liver enzymes in certain people that present much higher risks than average, too.

People taking daily cassia supplements/spoonfuls with statins, acetaminophen, methotrexate, isoniazid, antifungals, or regular alcohol need to know about this potential interaction.

Additionally, if cinnamon does actually produce some glucose-lowering as some of the messy individual trials we can all find online suggest, people on certain diabetes meds (like glipizide, glyburide, insulin, etc) might need to be careful about blood sugars going too low.

I’m going to keep enjoying cinnamon sometimes, maybe in smoothies, other rare times with melted butter and sugar on toast… and if I’m lucky again someday, on several pasteis de nata, gobbled down fresh out of a Manteigaria Bakery oven in Lisbon, Portugal:

Worth the whole trip. Seriously.

Though I’m not alarmist about this, I will probably take a look at the cinnamon in my pantry, and switch over to Ceylon cinnamon the next time I’m shopping.

If I currently have cassia-type in the pantry, I’ll keep the dosing to maybe a quarter-teaspoon at time, no more.

Speaking of which, I’m getting hungry for dinner, so I’m heading home now.

I won’t be recommending cinnamon for blood sugar regulation, especially in people with diabetes. There’s just not enough good evidence, and there are some risks.

Take good care!