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Quick answer
Cinnamon is a safe and tasty spice in normal food amounts. As a supplement for blood sugar, the evidence is inconsistent. Some reviews of trials found a small drop in fasting blood sugar in people with type 2 diabetes; others found no meaningful change in HbA1c, the long-term measure of blood sugar control that doctors use to guide treatment.
Cinnamon is not a treatment for diabetes. And the most common supermarket type, cassia cinnamon, contains coumarin, which can harm the liver if taken in large amounts every day.
Types of cinnamon
There are two main types, and the difference matters:
- Cassia cinnamon (Chinese or Indonesian cinnamon): the most common and cheapest type in many countries. Darker, with a strong flavour. Contains relatively high levels of coumarin.
- Ceylon cinnamon ("true cinnamon", from Sri Lanka): lighter, more delicate, made of thin rolled layers. Contains very little coumarin.
Most studies used cassia cinnamon, often 1 to 6 grams a day.
What the research says
Lab and animal studies suggest that compounds in cinnamon may improve how cells respond to insulin and slow the digestion of carbohydrates. Human results are mixed:
- A 2013 meta-analysis in the Annals of Family Medicine pooled 10 trials in people with type 2 diabetes. Cinnamon lowered fasting blood glucose by about 25 mg/dL (1.4 mmol/L) and improved cholesterol and triglycerides, but did not significantly change HbA1c. The studies varied widely in dose, duration and quality.
- Other reviews have found smaller effects or no benefit, and some trials in Western populations showed no improvement at all.
- In people with prediabetes, a small trial found a modest improvement in blood sugar response, but larger studies are needed.
Overall, if cinnamon has an effect, it is small and unreliable, much smaller than diet changes, exercise, weight loss or diabetes medicines.
How people use it
As food, cinnamon is a great way to add sweetness and flavour without sugar:
- Sprinkle on oats, yoghurt or fruit
- Add to coffee or tea instead of sugar
- Use in stews, rice and spice blends
If you are thinking about a supplement:
- Talk to your doctor or diabetes team first, especially if you take medicines that lower blood sugar.
- Choose Ceylon cinnamon if you plan to take cinnamon regularly in larger amounts, to limit coumarin.
- Keep cassia to small amounts. European food safety authorities set a tolerable daily intake for coumarin of 0.1 mg per kg of body weight. Cassia cinnamon can contain enough coumarin that about 1 to 2 grams a day (roughly half to one teaspoon) could reach this limit for a small adult.
- Check your blood sugar more often when you start, to look for any change and avoid lows.
Possible side effects and interactions
- Liver damage from coumarin, with large, regular amounts of cassia cinnamon, especially in people with liver disease
- Low blood sugar when combined with insulin or other glucose-lowering medicines
- Mouth irritation and allergic reactions: cinnamon flavouring can cause mouth sores (cinnamon contact stomatitis), a reaction dentists recognise that is often linked to cinnamon-flavoured chewing gum
- Bleeding risk: coumarin itself is not a blood thinner in these amounts, but people on warfarin should keep cinnamon intake consistent and tell their doctor about supplements
- Choking: the "cinnamon challenge" of swallowing a spoonful of dry powder is dangerous and has caused lung injury
Who should avoid cinnamon supplements
- People with liver disease (especially cassia cinnamon)
- People taking insulin or sulfonylureas, unless their doctor agrees and they monitor blood sugar
- People taking medicines that can affect the liver
- Pregnant or breastfeeding women (food amounts are fine)
- Children (food amounts are fine)
When to see a doctor
See a doctor if:
- You have symptoms of high blood sugar: excessive thirst, passing a lot of urine, tiredness, blurred vision, frequent infections or slow-healing wounds
- You have risk factors for diabetes (family history, overweight, high blood pressure, history of gestational diabetes) and have not been tested. Type 2 diabetes is common in the Gulf region and often has no symptoms early on.
- You have diabetes and your readings are regularly above your target, or you have hypoglycaemia (shakiness, sweating, confusion)
- You notice yellowing of the skin or eyes or dark urine
Frequently asked questions
How much cinnamon should I eat a day?
As a spice in food, there is no need to measure. For regular, larger amounts, prefer Ceylon cinnamon and keep cassia to under about half a teaspoon a day.
Can cinnamon replace metformin?
No. Metformin and other diabetes medicines have strong evidence for lowering blood sugar and preventing complications. Cinnamon does not.
Does cinnamon help with weight loss?
There is no good evidence that it does.
Is cinnamon tea helpful?
Cinnamon tea is a pleasant, sugar-free drink. It contains much less of the active compounds than the doses studied.
References
- National Center for Complementary and Integrative Health (NCCIH). Cinnamon. https://www.nccih.nih.gov/health/cinnamon
- Allen RW, et al. Cinnamon use in type 2 diabetes: an updated systematic review and meta-analysis. Annals of Family Medicine, 2013.
- European Food Safety Authority (EFSA). Coumarin in flavourings and other food ingredients with flavouring properties. EFSA Journal, 2008.
- German Federal Institute for Risk Assessment (BfR). Frequently asked questions about coumarin in cinnamon and other foods.