Cassia cinnamon does not change the insulin sensitivity or the liver enzymes in subjects with impaired glucose tolerance

Background: Published studies have reported conflicting results regarding the effects of cinnamon on glucose, lipids and insulin. To gain further insight into the metabolic effects of Cinnamomum cassia we performed randomized, double-blinded placebo-controlled study using euglycaemic-hyperinsulinaemic clamp.

Methods: Twenty-one subjects with impaired glucose tolerance (IGT) were included in the study (10 or 11 subjects in each group). The study groups were matched for age, gender and body mass index (BMI). Waist-to-hip ratio, BMI, blood pressure, fasting blood glucose, insulin, triglycerides, total cholesterol, low-density lipoprotein, high-density lipoprotein , HbA1c, ASAT, ALAT, bilirubin, ALP, GT and PK were measured before and after the intake of capsules equivalent to 6 g cinnamon twice a day for 12 weeks. The changes in insulin resistance were measured by euglycaemic-hyperinsulinaemic clamp. The Wilcoxon signed rank sum test, the Mann-Whitney U test and Pearson’s chi-squared test were used to analyse the data. Values of p < 0.05 were considered to indicate statistically significant differences.

Results: At enrolment, the groups were similar in terms of age, gender and BMI. Of the 21 randomized patients with IGT, 17 completed the study (8 controls vs. 9 treated). The ingestion of 6 g cinnamon twice a day for 12 weeks had no significant effect on insulin sensitivity, HbA1c, fasting glucose or BMI. No significant changes were seen in lipids or liver enzymes.

Conclusions: This study showed that ingestion of 6 g C. cassia twice a day for 12 weeks did not change the insulin sensitivity or liver enzymes in subjects with IGT.

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Alex’s Notes: I’m a sucker for cinnamon. Just like my love-affair with vinegar, I use cinnamon daily and quite literally put it on everything – from my post-workout potatoes to mixing it with stevia in my Greek yogurt. The main reason I do so is simple: cinnamon tastes good. The exception here is Ceylon cinnamon which tastes absolutely horrible, but I digress. My cinnamon of choice is the cassia variety (and henceforth this is the variety meant by “cinnamon” unless otherwise stated).

Now I fully admit that I have an ulterior motive for consuming cinnamon with everything. Cinnamon has demonstrated strong anti-oxidant, anti-microbial, anti-inflammation, anti-diabetic and anti-tumor activity, and been shown to reduce postprandial blood glucose levels in healthy subjects – an effect it is best known for. And just smack that digesting Ceylon variety again; the blood sugar effects don’t occur with its use. However, blood sugar is only a piece of the postprandial puzzle, and several studies have shown an effect of cinnamon on insulin sensitivity, albeit indirectly. In an effort to see if there truly is an effect on insulin sensitivity, the current study utilized a euglycaemic-hyperinsulinaemic clamp to measure it directly. Additionally, they also investigated the effects of cinnamon on liver enzymes because of concerns regarding the toxic natural compound coumarin.

Twenty-one subjects with impaired glucose tolerance (IGT; judged via an oral glucose tolerance test) were recruited for this randomized, double-blind, placebo-controlled study. Four dropped out, leaving 17 subjects (72-years old; BMI of 26.5 kg/m2) to consume a confusing amount of cinnamon. The researchers state that the subjects took one pill with breakfast and one pill with dinner every day for 12-weeks, and that the pills either contained 700mg of cellulose (placebo) or 200mg of cellulose plus 500mg of cinnamon (experimental). However, at every time-point after this the authors state that 12g of cinnamon was consumed daily (6g with breakfast & dinner).

I would assume the “one pill” was a mistake and that multiple pills were taken with the above amounts in each to equate 6g with each meal. That would be 12 pills per meal and could easily explain why one of the drop-outs did so because of difficulty swallowing the capsules. That would also mean the placebo group was consuming 8.4g of cellulose per meal, and this will make sense in a moment. The only significant changes after 12-weeks were a reduction in fasting insulin and an increase in insulin sensitivity in the placebo group, clearly indicating that the cellulose had an active effect. I honestly don’t see how this is surprising given that the placebo was providing an additional 12g of fiber daily (and this explains why two of the four dropouts complained of GI problems and were from this group). Why the researchers used cellulose instead of maltodextrin or some other benign powder is beyond me.

Aside from the above, neither group had any changes in fasting glucose, HbA1c, blood lipids, or liver enzymes. It appears that cinnamon may have some benefits to healthy persons, but the effects become more pronounced with worse glycemic control (e.g. diabetes).

Regarding courmarin, there is about 3000 mg/kg present in cinnamon, which equates daily ingestion of 36mg in the current study. This amount was clearly well tolerated for 12-weeks and provides strong relief regarding cinnamon consumption for upwards of 12g per day. So the bottom line here is to eat your fiber! Okay, sticking with cinnamon it appears that the effects go on both sides of the fence and with doses being well tolerated up to 12g per day there is no reason not to consume some cinnamon with your meals.

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