Cinnamon and Blood Sugar: What the Studies Show and Why Ceylon Is Not the Same as Cassia

It is just after seven. The porridge is steaming, the coffee machine is gurgling. And then it comes, like every morning: the heaping spoonful of cinnamon.

I take both questions seriously. Behind your morning spoonful is a good need: to do something for your metabolism yourself. That need deserves information you can rely on.

That is why I look at your cinnamon spoon from several directions: human studies, assessments by the German Federal Institute for Risk Assessment, BfR for short, toxicology and the KPNI lens. KPNI stands for clinical psychoneuroimmunology. It describes the interplay of nerves, hormones, the immune system and metabolism.

Can cinnamon lower blood sugar? What the meta-analyses show

You stir in the cinnamon and hope for a better number at your next check-up. Is that hope justified?

The hype began with a small study from Pakistan.

Many more studies have been published since then. They do not speak with one voice.

In 2019, a team led by Deyno from universities in Uganda and Ethiopia arrived at a similar picture with 16 studies. They included people with type 2 diabetes and with prediabetes. Fasting blood sugar fell by an average of 0.545 mmol/L, while HbA1c showed no significant change.

Imagine ten cooks who are all baking a cinnamon cake. Each one uses a different cinnamon, a different amount and a different oven. Nobody is surprised when the cakes turn out differently. That is exactly what the cinnamon studies look like.

Newer analyses: small effects, wide spread

A 2024 dose-response meta-analysis from Tabriz with 24 studies also reported lower values for fasting blood sugar and HbA1c, expressed as standardized effect sizes. As early as 2016, a team led by Costello reviewed eleven studies with 694 people. In ten of them, the participants continued taking their diabetes medication. Seven studies used cassia, only one used Ceylon cinnamon, and three did not name the type at all. The effects were modest. Only four studies reached the target values of the American Diabetes Association.

And now you know why I speak of a small signal with cinnamon and not of a treatment.

And in prediabetes? What small studies have observed

Prediabetes sounds like a waiting room. Not diabetes yet, but no longer quite carefree either. This is exactly where the thought comes easily: with cinnamon, I can slow this down.

There are also studies with no effect at all. A team led by Vanschoonbeek at Maastricht University gave 25 postmenopausal women with type 2 diabetes 1.5 g of cassia cinnamon daily for six weeks. Insulin sensitivity, glucose tolerance and blood lipids did not change.

And where effects do appear, they are usually modest. A team led by Lira Neto at the Universidade Federal do Ceará gave 160 people with type 2 diabetes, who continued taking their tablets, 3 g of cinnamon in capsules for 90 days. HbA1c fell 0.2 percentage points more than with placebo, and the team itself called the reduction modest.

And now you know why, with prediabetes, I talk about movement and food first, and only then about spices.

How might cinnamon work in the body? A look through the KPNI lens

Maybe you are wondering: if cinnamon does move something, how would that even work? A spice is not a medicine, after all.

Imagine your stomach as a floodgate. If it opens more slowly, sugar reaches your blood in small portions rather than as one big wave.

You can think of insulin as a key. It opens the doors of muscle and fat cells so that sugar from the blood can get in. This lock is exactly where the lab findings on cinnamon come in.

In 2012, a team led by Rafehi at the Baker IDI Heart and Diabetes Institute in Melbourne summarized the lab findings. In cell experiments, cinnamon improved insulin signaling pathways in muscle. In fat tissue, it increased the production of so-called PPAR receptors, comparable to a class of diabetes medications. Studies also showed anti-inflammatory properties. In humans, the review concluded, fasting blood sugar was the only value that improved with some consistency.

Through the KPNI lens, your cinnamon spoon touches several systems at once. In metabolism, it is about how well the insulin key opens the cell doors. In the hormonal system, gut hormones such as GIP play a part, helping to steer insulin release after meals. The immune system is involved because silent inflammation can dampen the action of insulin. And the nervous system brings the morning spoon itself into play: a ritual gives you something to hold on to, and that need is real.

And now you know why I distinguish so carefully between a lab finding and an everyday benefit.

Ceylon or cassia: why the difference in your jar matters for your liver

On the supermarket shelf, the label often says just one word: cinnamon. No type, no origin. How are you supposed to know what you are spooning every morning?

Once ground, the variations even out somewhat. The BfR found average values of around 3,000 mg per kg in cassia powder. In Ceylon cinnamon, its own measurements were at most 297 mg per kg.

Can you rely on the label? A label is a good start, but not proof. In a 2006 BfR assessment of cinnamon capsules, one product was labeled as Ceylon cinnamon. According to the BfR, the measured coumarin content of 2,300 mg per kg clearly pointed to cassia.

That leaves one hope: maybe the coumarin in the spice is bound so tightly that the body barely absorbs it? That is exactly what the BfR tested.

And now you know why the type on the package can matter more than the shape of your spoon.

How much cassia cinnamon is too much? The BfR limit in grams and on your spoon

Back to your morning. A heaping spoonful over your porridge, one in your coffee. Is that already a lot?

Where the limit of 0.1 mg per kilogram comes from

Coumarin used to be given as a medicine for lymphatic and venous congestion. Along the way, it became apparent that a small proportion of those treated responded with elevated liver values. In severe cases, this led to liver inflammation with jaundice, and in most cases it reversed.

How did the BfR arrive at its number? An expert report for Germany's Federal Institute for Drugs and Medical Devices analyzed 82 cases of possible coumarin-related liver damage. Even at the lowest doses of 25 to 30 mg daily, 10 percent of the cases still occurred. The BfR divided 25 mg by a safety factor of 5 and arrived at 5 mg per day. For a body weight of 60 kg, that corresponds to roughly 0.1 mg per kilogram. The European Food Safety Authority arrived at the same value using animal data.

Why do some people react sensitively? In humans, coumarin is mostly broken down via so-called 7-hydroxylation, a detoxification pathway. In rats and mice, by contrast, a pathway that produces toxic intermediates dominates. It has been discussed whether weaker 7-hydroxylation due to variants in the liver enzyme CYP2A6 makes some people more susceptible. A German study could not confirm this, and according to the BfR the cause remains unclear. I explain how liver enzymes process foreign substances in several steps in Liver detoxification phase 1 and phase 2.

The calculation, step by step

Briefly over the limit is not the same as permanently over it

The TDI is like a speed limit with a built-in safety margin. If you go a little too fast for a moment, you do not end up in the ditch right away. If you drive well over the limit every day, you use up the buffer. According to the BfR, slightly exceeding it for one to two weeks is not a cause for concern, for example during the Christmas season. The BfR sees a risk mainly when someone eats a lot of cassia cinnamon with a high coumarin content over a longer period.

Since 2011, EU maximum levels for coumarin have applied to ready-made foods containing cinnamon, for example 50 mg per kg for traditional cinnamon star cookies and 5 mg per kg for desserts such as rice pudding. For cinnamon as a spice in your kitchen, however, there is no maximum level.

How often does cinnamon as a food harm the liver? In 2012, the BfR had no reports of toxic liver inflammation after heavy cinnamon consumption, with the exception of one suspected case in a young woman who had eaten a particularly large amount of cinnamon in the preceding weeks. In 2019, a systematic review by a team led by Hajimonfarednejad in Shiraz collected studies, case reports and spontaneous reports. The most common problems were gastrointestinal complaints and allergic reactions, mostly temporary. For medicinal use at higher doses or over longer periods, the team recommends medical monitoring.

And now you know why, with cinnamon, I ask about type and amount first, and only then about blood sugar.

Cinnamon capsules and diabetes medication: where caution makes sense

The capsule looks like the serious version of the spoon. Measured, neat, almost like a medicine. That is exactly what makes it so tempting.

At 6 g of cassia daily, the highest dose in the study from Pakistan, an average content would add up to 18 mg of coumarin. According to the BfR, that corresponds to 0.3 mg per kilogram at 60 kg, which is three times the TDI. The BfR considered cinnamon products for lowering blood sugar to be medicines in principle. They would need proof of efficacy, a record of side effects such as hypoglycemia, and testing for interactions. Germany's Federal Institute for Drugs and Medical Devices and the German Diabetes Society shared this position.

Cinnamon plus medication: why you should not simply add them up

In ten of the eleven studies in Costello's review, the participants continued taking their diabetes medication. According to the BfR, as of 2006 there had been no testing for hypoglycemia and interactions of the kind that is standard for medicines. A team led by Necyk at the University of Alberta in Canada points out that natural products with blood sugar lowering properties could promote hypoglycemia when combined with medication.

This mainly concerns medications that can cause hypoglycemia on their own, such as insulin or sulfonylureas. My advice: never take cinnamon products as a silent add-on. Let your doctor know, measure more often in the first weeks and never change your medication on your own.

And Ceylon capsules? First studies with extracts

In 2006, the BfR wrote that it was not known whether Ceylon cinnamon affects blood sugar in a similar way to cassia. Since then, the first randomized trials with standardized extracts have come from Sri Lanka, the country of origin of Ceylon cinnamon.

A second study from Sri Lanka with 150 adults and 1,000 mg of extract daily missed its primary goal, a reduction in LDL cholesterol. Fasting blood sugar, on the other hand, fell 8.59 mg/dL more than with placebo, especially in people with diabetes. It was funded by the manufacturer of the extract, and the coumarin content was 0.01 percent. Important: both studies used standardized extracts, not kitchen powder. The results cannot simply be transferred to your spoon.

The European Medicines Agency describes Ceylon cinnamon bark as a traditional herbal medicinal product, based on long-standing use. Its indications are mild, cramp-like gastrointestinal complaints with bloating and flatulence, as well as mild diarrhea. The monograph does not mention blood sugar.

And now you know why a cinnamon capsule belongs on your medication list, not just in your kitchen.

Why cinnamon capsules are no substitute for movement and meal structure

To be honest: the spoon is convenient. It asks nothing of you except a flick of the wrist in the morning. Movement and new eating habits, by contrast, feel like work.

These numbers measure different things than the cinnamon studies, so I do not offset them directly against each other. But they show where research sees the bigger levers: in movement, muscle work and meal structure.

I describe in detail how movement can affect blood sugar after meals in Movement and blood sugar after meals. You can read why your muscles are a large sugar store in Strength training for diabetes and insulin resistance. And how you can recognize insulin resistance in Recognizing insulin resistance.

And now you know why I would rather talk about your walk after dinner than about your cinnamon spoon.

What can you actually do now?

You do not have to throw out your cinnamon. You can use it more consciously.

Maybe behind your morning spoonful is the need to have your blood sugar in your own hands. A first step could be to know your numbers instead of counting spoonfuls.

You can read what fasting may have to do with insulin resistance in Fasting, blood sugar and insulin resistance. And I describe how milk thistle and liver values are connected in Milk thistle for fatty liver.

Frequently asked questions about cinnamon and blood sugar

Further reading in the ViveCura guide

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