Cinnamon, Spice and Everything Nice: Insulin-Sensitizing Spices
Eric Yarnell, ND, RH(AHG)
In recent years, several common spices have received attention as possible insulin sensitizers. Many of these spices, including Cinnamomum spp (cinnamon, cassia) bark and Syzygium aromaticum (clove) flower buds, were once central players in the spice trade. These and similar flavorful, well-known herbs could become critical components for helping people overcome or avoid metabolic syndrome and diabetes mellitus.
Cinnamon and Cassia
True cinnamon is rarely encountered on supermarket shelves in North America, as it has largely been replaced by the milder, cheaper Cinnamomum cassia (cassia). Long-esteemed in traditional Chinese herbal medicine, where it is known as rou gui, cassia and cinnamon are not identical. This herb has perhaps the strongest support as a potential clinically important insulin sensitizer.
Recently, two clinical trials assessed whether cassia influences insulin activity and other parameters of diabetes. The first clinical trial involved 60 adult men and women with non-insulin-dependent diabetes mellitus in Pakistan (Khan et al., 2003). In this randomized, double-blind, placebo-controlled crossover trial, daily intake of 1g, 3g or 6g of cassia bark powder in capsules all reduced mean fasting serum glucose, triglyceride, LDL cholesterol and total cholesterol levels significantly compared to the baseline, while no such changes occurred in the placebo group. Supplementation lasted 40 days. This trial was weakened by failure to do between-group statistical comparisons.
A more recent double-blind trial randomized 25 post-menopausal women to take either 1.5g cassia or placebo daily for 42 days (Vanschoonbeek et al., 2006). No effects on lipids or glucose tolerance were seen in either group. It is not clear why this study did not confirm the results of the previous trial. Though a relatively lower dose was used, the prior study detected no obvious dose-response curve. The study population was different than the mixed-sex group who participated in the first trial. Both ran for a relatively short period of time. A larger study using a moderately larger dose of true cinnamon as well as cassia in a mixed-sex group is needed to help clarify the efficacy of this herb.
Cinnamon and cassia appear to work due to maximizing insulin receptor function (Imparl-Radosevich et al., 1998; Jarvil-Taylor et al., 2001). They do not stimulate pancreatic insulin synthesis, and thus will not worsen insulin resistance. It is believed that the tannin component of the spices has insulin-sensitizing effects, as opposed to the volatile terpenoids so well known as antimicrobials and flavoring agents.
The genus Sygyzium (formerly included in Eugenia) contains the familiar spice S. aromaticum (clove). An extract of clove flower buds has been shown to have insulin-sensitizing effects in adipocytes and hepatocytes (Prasad et al., 2005). No human data are available.
Clove’s less well-known (in North America) cousin, S. cumini (jambol, rose apple), has been much more widely studied for this purpose. Traditionally, the fruit and seed have been used for people with diabetes. One double-blind trial tested whether an infusion of the leaves (2g/L water) could affect plasma glucose levels compared to glyburide and an infusion of Imperata braziliensis (Brazilian satintail), a plant with no known antidiabetic activity, or placebo in 27 patients (Teixeira et al., 2004). Plasma glucose levels fell significantly in the glyburide and Imperata group compared to the placebo and jambol groups after two weeks, suggesting that jambol is at the very least not effective in such a short time period, at the specific dose and/or using an aqueous leaf extract. Successful animal studies have used seed powder doses as high as 500mg/kg (Sridhar et al., 2005).
Other members of this genus have also shown some potential in pre-clinical studies. S. cordatum (water berry) leaf lowered glucose levels in diabetic rats in one study (Musabayane et al., 2005). None of the herbs mentioned have any known adverse effects beyond mild nausea at reasonable doses. Given all of this, much more research is warranted to determine the efficacy of extracts of various members of this genus based more closely on traditional uses.
The beautiful fruit of Myristica fragrans (nutmeg), until now, has been primarily considered a delayed-onset hypnotic, helping people who tend to wake up in the night stay asleep, and as a carminative. A new study suggests that a methanol extract of the seed contains lignans and other polyphenolic constituents with insulin-sensitizing effects (Yang et al., 2006). This fits with the traditional use of nutmeg in southern Asia for people with diabetes. An as-yet unpublished paper presented at the British Pharmaceutical Conference (Sept. 4-6) by lead researcher Rahul Somani found that nutmeg extract was effective at reducing plasma glucose and lipids in diabetic rats, though the research group suggested this was due to stimulation of pancreatic insulin production. Such an effect is potentially a serious problem, both due to the potential for causing beta-cell burnout and because raising insulin production will only aggravate insulin resistance. Further study is necessary.
Many other common spices have already been fairly well established as part of a program for metabolic syndrome and diabetes, including but not limited to Trigonella foenum-graecum (fenugreek); Allium cepa (onion); Ocimum sanctum (holy basil), common in Indian cuisine; and Momordica charantia (bitter melon), common in Southeast Asian cuisine (Yeh et al., 2003). These flavorful, food-based therapies could prove clinically helpful in improving insulin sensitivity and thus preventing or reversing metabolic syndrome and/or diabetes.
Imparl-Radosevich J et al: Regulation of phosphorylase phosphatase (PTP-1) and insulin receptor kinase by fractions from cinnamon: Implications for cinnamon regulation of insulin signaling, Horm Res 50:177-82, 1998.
Jarvill-Taylor KJ et al: A hydroxychalcone derived from cinnamon functions as a mimetic for insulin in 3T3–L1 adipocytes, J Am Coll Nutr 20:327-36, 2001.
Khan A et al: Cinnamon improves glucose and lipids of people with type 2 diabetes, Diabetes Care 26:3215-8, 2003.
Musabayane CT et al: Effects of Syzygium cordatum (Hochst.) [Myrtaceae] leaf extract on plasma glucose and hepatic glycogen in streptozotocin-induced diabetic rats, J Ethnopharmacol 97:485-90, 2005.
Prasad RC et al: An extract of Syzygium aromaticum represses genes encoding hepatic gluconeogenic enzymes” J Ethnopharmacol 96(1-2):295-301, 2005.
Sridhar SB et al: Preclinical evaluation of the antidiabetic effect of Eugenia jambolana seed powder in streptozotocin-diabetic rats, Braz J Med Biol Res 38(3):463-8, 2005.
Teixeira CC et al:Syzygium cumini (L.) Skeels in the treatment of type 2 diabetes: Results of a randomized, double-blind, double-dummy, controlled trial, Diabetes Care 27:3019-20, 2004.
Vanschoonbeek K et al: Cinnamon supplementation does not improve glycemic control in postmenopausal type 2 diabetes patients, J Nutr 136:977-80, 2006.
Yang S et al: Inhibition of protein tyrosine phosphatase 1B by lignans from Myristica fragrans, Phytother Res 20(8):680-2, 2006.
Yeh GY et al: Systematic review of herbs and dietary supplements for glycemic control in diabetes, Diabetes Care 26:1277-94, 2003.
Eric Yarnell, ND, RH(AHG), is a graduate of Bastyr University. He completed a two-year residency with Silena Heron, ND, and served as chair of botanical medicine at the Southwest College of Naturopathic Medicine. He is past senior editor of the Journal of Naturopathic Medicine. Dr. Yarnell is a founding member and current president of the Botanical Medicine Academy and author of numerous textbooks and articles, including Naturopathic Urology and Men’s Health, Naturopathic Gastroenterology and Clinical Botanical Medicine. His area of clinical focus is urology and men’s health. He is assistant professor in botanical medicine at Bastyr University.