1–3 g/day. For continued use, prefer Ceylon cinnamon.
Weak/mixed · ≈ −10 to −19 mg/dL — strong on glucose, weak on HbA1c
View the study (meta-analysis) →⏱ 3 min read
Cinnamon is a spice used for millennia in every culinary culture in the world, but modern pharmacology has confirmed over the last two decades that its action on glucose metabolism goes beyond folklore: small doses (1–6 grams daily) modestly reduce fasting blood glucose and HbA1c in people with type 2 diabetes or prediabetes, an effect that is consistent across meta-analyses and is obtained with an intervention that costs pennies a day.
There are two main species of cinnamon on the market, with very different toxicological profiles: Ceylon cinnamon (Cinnamomum verum) has a low coumarin content and is considered safe for long-term use, whereas cassia cinnamon (Cinnamomum cassia or aromaticum, the most common in supermarkets and cheap supplements) has a high coumarin content that can be hepatotoxic with prolonged high intake, an important difference when choosing a product.
The strongest evidence for cinnamon concerns blood glucose: several meta-analyses of randomized trials have shown modest reductions in fasting blood glucose (10–30 mg/dL) and HbA1c (0.1–0.3 points) in people with type 2 diabetes or prediabetes, with doses of 1–6 grams daily of cinnamon powder or extract for 4–16 weeks; the effect is comparable to other mild nutritional interventions for blood glucose.
The most plausible mechanism combines modulation of peripheral insulin sensitivity (with effects on the translocation of the GLUT4 transporter to skeletal muscle), inhibition of digestive enzymes that release glucose (alpha-amylase, alpha-glucosidase), and an antioxidant effect that reduces the oxidative stress associated with the chronic hyperglycemic state.
On the lipid profile, meta-analyses show modest but significant reductions in total cholesterol, LDL, and triglycerides, together with modest increases in HDL, in people with type 2 diabetes; the effect on lipids in people without diabetes is less consistent, which suggests that part of cinnamon's cardiovascular benefit is mediated by the improvement in underlying glycemic control.
In digestion and gastric emptying, several small studies have shown that cinnamon slows gastric emptying and reduces the postprandial glucose peak when consumed with meals, a useful property for people prone to reactive hypoglycemia or exaggerated glucose spikes after eating refined carbohydrates.
In polycystic ovary syndrome, several small trials have shown improvements in menstrual regularity and in markers of insulin resistance with doses of 1.5–3 g/day over several months, in line with the general effect on insulin sensitivity that appears to be the central mechanism of most of its clinical applications.
The most efficient way to obtain effects on blood glucose is 1–3 grams daily of Ceylon cinnamon powder (no more, to avoid coumarin even if it is Ceylon), whether sprinkled on meals (coffee, yogurt, oatmeal, smoothies), in standardized capsules, or as an aqueous extract (which preserves the active water-soluble compounds without the fat-soluble coumarin); clinical effects on metabolic markers appear between 4 and 12 weeks.
The most important precaution is to choose Ceylon cinnamon rather than cassia for continued use: 1 gram daily of cassia can contain up to 5 milligrams of coumarin, close to the safety limit set by the EFSA (0.1 mg/kg/day); people with preexisting liver disease, those taking hepatotoxic drugs, or those combining cinnamon with anticoagulants (coumarin has intrinsic anticoagulant activity) should be especially cautious; in pregnancy, it is recommended to limit consumption to usual culinary use.
Information, not medical advice. Scientific evidence reflects the quality of the studies.