Effectiveness of Cinnamon for Lowering Hemoglobin A1C in Patients with Type 2 Diabetes: A Randomized, Controlled Trial

Recruitment

Patients were contacted by volunteers and invited to attend an informational session about the study. One hundred ninety patients were contacted and 116 agreed to attend informational sessions. They were conducted on a rolling basis, with several sessions a week at various times, and the principal investigator or an assistant presented details about the study, distributed and explained informed consent documents, and answered questions. One hundred nine patients agreed to participate and signed informed consent documents at the information sessions (Figure 1). No compensation was offered to volunteers.

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Figure 1.

Randomization diagram with reasons for exclusion and complete accounting of patients.

Standard demographic data and information regarding the number of diabetes medications, insulin use, and cinnamon intake were collected via an 11-question survey developed by the investigator and tested for clarity on 5 diabetic patients before the study (Table 2). Responses regarding medication use were confirmed in the medical record. Participants were queried about current cinnamon intake (normal, no addition to diet; high, supplemented to diet in any amount or type, ie, capsules, powder, syrup). Participants were asked to continue their pretrial level of cinnamon intake.

Randomization

We randomized patients by blocking (a technique designed to ensure that the treatment and control groups are of similar size) in groups of 10. Marked papers were prepared by a person not otherwise involved with the research team; half of each block of 10 was marked “treatment” and the other half was marked “control.” These were pulled from a box at the time of consent, so allocation was concealed until that time. Neither participants nor investigators were blinded, but the laboratory (true outcome assessor) was blinded to group allocation.

After randomization, all patients were instructed to follow up for their diabetes care as they normally would during the subsequent 90 days. All patients were allowed to adjust their usual medications and doses as recommended by their physician. Each patient had a serum, nonfasting HbA1c drawn on day 0 and again at day 90 to 95. Those patients randomized to take cinnamon received 180 capsules (500 mg each) of Cinnamomum cassia (Puritan's Pride, Oakdale, NY) from the 96th Medical Group pharmacy at the time of randomization. They were instructed to take 2 capsules daily with food in addition to their normal medications. Those randomized to usual care were instructed to take their normal medicines and follow up with their physician as per their normal schedule. The investigator contacted participants by phone and letter at 80 to 88 days after randomization to remind them to have their blood drawn. In addition, information regarding medication changes and cinnamon compliance was collected at this time. All participants had laboratory blood draws done at the same accredited laboratory using the same assay (G7 High Performance Liquid Chromatography Analyzer, Tosoh, Tokyo, Japan).

To determine a power of 0.80, we calculated a sample size of 126, with α = 0.05 (SD, 1). The effect size considered to be clinically significant was a 0.5% lowering of HbA1C.

We analyzed the primary outcome by an unpaired 2-sample t test (mean difference between baseline and final HbA1C). The data sets were normally distributed. An intention-to-treat analysis was performed. Missing data because of withdrawals or noncompliance were dealt with by carrying forward the last known value for HbA1C.

The Institutional Review Board of the 59th Medical Wing, Wilford Hall Medical Center, approved this trial, and the voluntary fully informed consent of the patients used in this research was obtained as required by Title 32 Code of Federal Regulations 219 and Air Force Instruction 40-402.

Strengths and Weaknesses of This Study

This trial was strengthened because it was an effectiveness trial that described community clinical practice and it measured outcomes that are important to diabetes care providers. Trials of efficacy are appropriate to identify whether an intervention works, but without effectiveness data in the types of patients who will receive the intervention it is difficult for clinicians to determine whether to incorporate it into their practice.

We used standard, off-the-shelf cinnamon capsules that patients would find at their local stores or on the Internet. We did not test these capsules for purity because there is no regulation of cinnamon as a food supplement and we wanted to mimic cinnamon that patients would buy on their own.

The primary reason that no placebo was used in this study was the strong taste of cinnamon capsules. This precluded any blinding of patients because they would know within minutes whether they had taken the treatment or not. This lack of placebo made it difficult to prove beyond any doubt that the cinnamon itself versus the daily reminder to take the cinnamon provided was the cause of the lowered HbA1C.

Recruitment stopped before reaching the predicted sample size because of the unplanned relocation of the investigator. A statistically significant benefit is still seen with fewer numbers.

Strengths and Weaknesses in Relation to Other Trials

Previous trials have shown conflicted results about the efficacy of cinnamon to treat diabetes. These trials have a variety of shortcomings: they generally studied well-controlled patients with type 2 diabetes^7,8,10; some only measured fasting glucose⁶; some measured HbA1C after as little as 30 days’ time⁷; some had narrow age, sex, or racial limits to their study populations^6–9; all excluded insulin use and comorbid conditions; and none allowed medication changes. Only one included a power analysis.¹⁰ Although meta-analysis of these trials¹¹ is interesting, the diverse nature of the trials makes it very difficult to draw useful conclusions from a combined analysis.

There are several reasons why this current trial may have shown benefit where earlier trials did not. First, this is the largest randomized cinnamon trial to date in type 2 diabetics. Second, we were more likely to see a treatment effect because we studied only patients with poorly controlled type 2 diabetes. Third, it is possible that the inclusion of patients using insulin and those with comorbid conditions potentiated the effect of cinnamon, but this is unlikely because the groups were similar. Finally, diabetics in the United States may have different characteristics than those in other countries.

The Meaning of This Study

This study gives diabetes care providers and diabetic patients an easily accessible, likely safe, and cheap alternative to help treat type 2 diabetes. According to the United Kingdom Prospective Diabetes Study,¹² a drop of HbA1C from 7.9% to 7% lowers the risk of macrovascular disease 16%, retinopathy 17% to 21%, and nephropathy 24% to 33%; thus, a 0.83% drop in HbA1C levels in patients might be expected to yield similar reductions in morbidity.

Unanswered Questions and Future Research

Whether there is synergy between cinnamon and prescription medications (including insulin) is a topic for further research. Some have postulated that lipids are lowered by the use of cinnamon. Because one of the proposed mechanisms of cinnamon is increased insulin sensitivity, the treatment of patients with the metabolic syndrome with adjunct cinnamon may yield weight loss, improved lipid profiles, and better glucose tolerance. Both in vitro and in vivo animal studies have shown that cinnamon is an insulin sensitizer.² Several compounds within cinnamon have been identified as possible sources of this sensitization process.