Cinnamon: an aromatic condiment applicable to chronic kidney disease

Article information

Kidney Res Clin Pract. 2023;42(1):4-26

Publication date (electronic) : 2023 January 31

doi : https://doi.org/10.23876/j.krcp.22.111

Laís de Souza Gouveia Moreira¹, Isabela de Souza da Costa Brum¹, Drielly C. M. de Vargas Reis², Liana Trugilho¹, Tuany R. Chermut³, Marta Esgalhado⁴, Ludmila F. M. F. Cardozo⁴, Peter Stenvinkel^,5, Paul G. Shiels⁶, Denise Mafra^1,3,7

¹Graduate Program in Medical Sciences, Fluminense Federal University, Niterói, Brazil

²Graduate Program in Clinical Medicine, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil

³Graduate Program in Nutrition Sciences, Fluminense Federal University, Niterói, Brazil

⁴Graduate Program in Cardiovascular Sciences, Fluminense Federal University, Niterói, Brazil

⁵Division of Renal Medicine, Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Stockholm, Sweden

⁶Institute of Cancer Sciences, College of Medicine, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK

⁷Graduate Program in Biological Sciences – Physiology, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil

Correspondence: Peter Stenvinkel Division of Renal Medicine, Department of Clinical Science, Intervention and Technology, Karolinska University Hospital M99, 141 86 Stockholm, Sweden. E-mail: Peter.Stenvinkel@ki.se

Received 2022 May 30; Revised 2022 July 4; Accepted 2022 July 14.

Abstract

Introduction

Cinnamon is a spice used for centuries as a culinary flavoring agent with organoleptic properties in different cultures worldwide. It has been used traditionally as a remedy for respiratory and gastrointestinal complications and has been widely studied because of its potential health-promoting properties [1]. These include antioxidant, anti-inflammatory, antimicrobial, antidiabetic, anticancer, and antilipemic properties [2–4].

The anti-inflammatory properties of cinnamon have been suggested to be derived via inhibition of nuclear factor kappa B (NF-κB) expression and consequently reduced production of proinflammatory cytokines, such as tumor necrosis factor (TNF), C-reactive protein (CRP), and interleukin (IL) 6 [5–7]. Cinnamon also promotes the activation of nuclear factor erythroid 2-related factor 2 (Nrf2), which upregulates a host of cytoprotective defenses and increases the synthesis of antioxidant enzymes such as catalase (CAT), heme oxygenase 1 (HO-1), glutathione peroxidase 1 (GPx-1), and NAD(P)H dehydrogenase [quinone] 1 [6–9].

Patients with chronic diseases, including chronic kidney disease (CKD), commonly present with systemic inflammation and oxidative stress, dysregulated glucose and lipid metabolism, variations in blood pressure, and, consequently, a higher risk of cardiovascular disease (CVD) [10]. Furthermore, these patients may present with an altered composition of gut microbiota associated with increased uremic toxin levels in the circulation, exacerbating oxidative and inflammatory burdens [11].

The concept of food as medicine (nutrients and bioactive compounds are obtained from food) has been used to promote health and mitigate the chronic burden of lifestyle diseases [12]. Foods such as turmeric, propolis, Brazil nut, beetroot, berries, and cruciferous vegetables have documented benefits in patients with CKD, including control of inflammation, oxidative stress, and gut dysbiosis [13–19].

Few studies have been conducted on the effects of regular cinnamon consumption in patients with CKD. Therefore, in this narrative review, we summarize the beneficial effects of cinnamon and its possible role as a nonpharmacologic adjuvant therapy for complications associated with CVD, diabetes, obesity, and gut dysbiosis in patients with CKD to explore its medicinal benefits for these high-risk patient groups.

Cinnamon

Cinnamon is an indigenous spice obtained from the inner bark of trees belonging to the genera Cinnamomum from the Lauraceae family. It has been used since as early as 3,000 BC in Egypt. The name is of Greek origin (kinnámōmon), which translates as ‘sweet wood’ [20]. Today, it is used daily in various cuisines worldwide. Despite there being several varieties of cinnamon, only two, Ceylon cinnamon (also known as true cinnamon, which originates mainly from Sri Lanka) and cassia cinnamon (which originates from China, Vietnam, and Indonesia), are available in American and European food markets (Table 1) [2,21].

Table 1.

Varieties of cinnamons and origins

Cinnamon contains carbohydrates (52%), fibers (33%), protein (3.5%), and fat (4%). This spice is also a source of potassium (134.7 mg/g), magnesium (85.5 mg/g), calcium (83.8 mg/g), phosphorus (42.4 mg/g), manganese (20.1 mg/g), and iron (7.0 mg/g) [22]. The key components of cinnamon are essential oils of trans-cinnamaldehyde, cinnamyl acetate, and eugenol; a range of bioactive resinous compounds including cinnamaldehyde, cinnamic acid, and cinnamate; water-soluble polyphenols such as catechin, epicatechin, procyanidin, quercetin, and kaempferol; and polyphenolic polymers [23,24]. Eugenol is the main compound in the leaves, whereas cinnamaldehyde is predominant in the bark and camphor in the root [2,23,25]. The spicy flavor and fragrance characteristics of cinnamon are due to cinnamaldehyde (known as cinnamic aldehyde). In addition, the aging of cinnamon leads to color darkening due to higher levels of resinous compounds [25].

The daily intake of cinnamon can be considered safe if it does not exceed the tolerable daily intake of coumarin (0.1 mg/kg of body weight) [2], which is a phytochemical with anticoagulant, carcinogenic, and hepatotoxic properties [2,26]. However, coumarin concentration depends on the type of cinnamon, e.g., cassia cinnamon contains significant amounts of coumarin, whereas Ceylon cinnamon contains only trace quantities [2].

Different species of cinnamon may present an array of other oils with diverse characteristics, and their effects have been widely debated. Various studies have used different species and forms of cinnamon supplementation, leading to equivocal findings [1,27,28].

Cinnamon: antioxidant and anti-inflammatory actions

High production of reactive oxygen species (ROS) and reactive nitrogen species and reduced antioxidant capacity lead to oxidative stress, which promotes the pathogenesis of several chronic diseases, including diabetes, CKD, and CVD [29,30]. Therefore, modulating antioxidant enzyme production can reduce ROS formation and oxidative stress, slowing chronic disease progression [31]. Various cinnamon extracts, such as Cinnamomum zeylanicum Blume essential oil, ethanol extracts of cinnamon bark, cinnamon bark aqueous extract, and methanolic crude extract of Cinnamomum verum, display antioxidant activity, which indicates the potential for cinnamon to manage oxidative stress-related disorders [32]. Most cinnamon studies in vitro and in vivo (Table 2) [9,33–47] demonstrate significant antioxidant activity through multiple mechanisms, including reduction of malondialdehyde level (lipid peroxidation marker), activation of transcription factor Nrf2, and synthesis of antioxidant enzymes such as HO-1, superoxide dismutase, CAT, and GPx [48,49]. Twenty-two chemical ingredients have been isolated from cinnamon in addition to cinnamaldehyde analogues; of these, lignan pinoresinol (PRO) and the flavonol (–)-(2R,3R)-5,7-dimethoxy-3', 4'-methylenedioxy-flavan-3-ol (MFO) display antioxidant capacity [50].

Table 2.

Studies involving cinnamon and antioxidant and anti-inflammatory actions

The primary mechanism by which cinnamon (principally the cinnamaldehyde component) acts as an anti-inflammatory is via the downregulation of NF-κB [33,51] and diminution of inflammatory cytokine expression (e.g., TNF, CRP, and IL-6). Cinnamon also appears to reduce the levels of IL-1β and IL-18 by inhibiting the expression of NLR family pyrin domain containing 3 inflammasome and caspase-1 [34].

Additionally, cinnamaldehyde suppresses the expression of cyclooxygenase 2, nitric oxide synthase and prostaglandin E2 (PGE2) [52,53]. It has been implicated in the decreased phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinases (p38 MAPKs) pathways [35]. The role of cinnamon as an antioxidant and anti-inflammatory agent is illustrated in Fig. 1.

Figure 1.

Antioxidant and anti-inflammatory actions of cinnamon in cells.

Bioactive compounds from cinnamon may activate the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), leading to the synthesis of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), heme oxygenase 1 (HO-1), glutathione peroxidase 1 (GPx-1), and NAD(P)H dehydrogenase [quinone] 1 (NQO-1). Also, these compounds can inhibit nuclear factor kappa B (NF-κB), activator protein 1 (AP-1), and NLR family pyrin domain containing 3 (NLRP3), reducing inflammatory cytokine production.

TLR-4, toll-like receptor 4; ERK, extracellular signal-regulated kinase; AKT, protein kinase B; Keap1, Kelch-like ECH-associated protein 1; TNF-α, tumor necrosis factor alpha; CRP, C-reactive protein; IL, interleukin.

A limited number of studies have described the anti-inflammatory effects of cinnamon in humans, but the results remain inconclusive. Supplementation of 1.5 g/day of Cinnamomum burmannii powder in women with rheumatoid arthritis for 8 weeks promoted a reduction in both visual and pain scales, reduced tender and swollen joint counts, and reduced serum CRP and TNF levels [5]. Similarly, cinnamon (1.8 g/day for 2 months) in patients with migraines reduced serum IL-6 and nitric oxide (NO) levels [54]. The frequency, severity, and duration of migraine attacks decreased, suggesting a reduction in the inflammatory process [54]. In contrast, Davari et al. [51] used 3 g/day of cinnamon for 8 weeks in patients with type 2 diabetes (T2D). They found no beneficial effects on NF-κB, sirtuin 1 (SIRT1), or other systemic inflammation markers, including IL-6 and high-sensitivity CRP. The reasons for this outcome disparity remain unclear and may be multifactorial, including differing cinnamon sources, purity, and experimental methodologies.

Diabetes and cinnamon

Diabetes is one of the leading causes of CKD, manifesting as diabetic kidney disease. Several studies (Table 3) [51,55–78] have proposed that cinnamon therapy can improve insulin action and glucose metabolism, with procyanidin type-A polymers and cinnamaldehyde being the primary components associated with the antidiabetic effects [79].

Table 3.

Studies involving cinnamon and diabetes

Procyanidin type-A polymers in cinnamon can mimic insulin action as they increase insulin receptor autophosphorylation of β-subunit tyrosine residues and reduce oxidative stress in pancreatic β-cells [80,81]. Moreover, cinnamon extract (C. zeylanicum) ameliorated glucose transporter 4 translocation via the adiponectin and intracellular 5' adenosine monophosphate-activated protein kinase (AMPK) signaling pathway [82,83] and through stimulation of liver kinase B1 mediated AMPK phosphorylation [84].

Additionally, inhibition of α-glucosidase and pancreatic α-amylase, which promote postprandial glycemic amelioration, has been attributed to the action of the cinnamon extract [85].

Cinnamon also induces the expression of the peroxisome proliferator-activated receptors (PPAR) alpha and gamma (PPAR-α and PPAR-γ) in vitro and in vivo. This is notable as these regulate adipogenesis and insulin resistance by regulating the expression of genes encoding proteins involved in adipokine synthesis, adipocyte differentiation, and lipid and carbohydrate metabolism [86]. Additionally, cinnamaldehyde may stimulate the expression of PPAR-γ and PPAR delta (PPAR-δ) in differentiated adipocytes, promoting insulin sensitivity and fatty acid β-oxidation in adipose tissue and skeletal muscle [87]. Another component of cinnamon extract, the B-type procyanidin C1, has been demonstrated to stimulate preadipocyte differentiation as well as act as a potential insulin sensitizer through the protein kinase B (AKT)/endothelial NO synthase (eNOS): AKT/eNOS pathway in mature adipocytes [88]. The phosphoinositide 3-kinase (PI3K)/AKT pathway participates in glucose uptake by skeletal muscles, adipose tissues, and liver. Cinnamaldehyde treatment (10 mg/kg) has been reported to increase the expression of insulin receptor substrate 1 (IRS-1), PI3K, and AKT2 in diabetic rats, promoting enhanced insulin signaling by the IRS1/PI3K/AKT pathway and reducing insulin resistance and promoting an antidiabetic effect [55].

Despite the salutogenic effects of cinnamon treatment in diabetes, other human-based studies have yielded equivocal results. In one systematic review, no significant benefits were found for cinnamon in reducing glucose and glycated hemoglobin (HbA1c) levels in patients with type 1 diabetes [89]. Conversely, a meta-analysis has reported that intake of whole cinnamon or cinnamon extract lowered fasting blood glucose (FBG) in T2D and prediabetes [90]. In a meta-analysis of 435 patients, Akilen et al. [91] reported that cinnamon doses ranging from 1 to 6 g/day ingested for between 40 days and 4 months reduced HbA1c and fasting glycemia levels. In 2013, a further meta-analysis including 543 patients reported that cinnamon supplementation (powdered cinnamon and aqueous extract) ranging from 120 mg to 6 g ingested for between 4 and 18 weeks reduced blood glucose, total cholesterol, and triglycerides but did not affect HbA1c level [92]. Costello et al. [80] have shown that cinnamon dietary supplements (doses ranging from 120 to 6,000 mg/day ingested for between 4 and 16 weeks) have clinically meaningful effects on glycemic control (FBG or HbA1c) in patients with T2D.

Additionally, a meta-analysis showed no effect of powdered cassia cinnamon intake (1–2 g) on fasting glucose, HbA1c, triglycerides, low-density lipoprotein (LDL), and total cholesterol levels in patients with T2D. On the other hand, a higher (at least 3 g) rather than a lower dose of cassia bark powder or cassia extract associated with lifestyle and diet protocols was more effective for glucose control in T2D [93].

Analyzing the impact of cinnamon on patients with diabetes is very complex as cinnamon contains several compounds, such as coumarin, cinnamic acid, cinnamaldehyde, cinnamic alcohol, and eugenol, with varied concentrations among species [94]. In addition, results are related to the quality of cinnamon, the type of branches, and manufacturing practices among species and formulations [95].

The effectiveness of cinnamon in glucose control may depend on how well the diabetes was controlled during the study. In addition, previous studies have used different parameters and periods [95]. Therefore, administering cinnamon can be a helpful add-on therapy in integrative medicine for managing T2D. Still, long-term trials are required to establish the efficacy and safety of cinnamon. In addition, the differing contributions of various microbiomes between subjects must be addressed [96].

Cinnamon: benefits in obesity

Obesity is a strong predictor of renal dysfunction and CKD [97]. Some physiological responses of the kidneys to obesity include increased glomerular filtration rate, tubular reabsorption of sodium, filtration fraction, and renal plasma flow [98]. Central obesity and abdominal fat are risk factors for metabolic syndrome, which is also associated with the development and progression of CKD and CVD [99].

Cinnamon has been studied as a potential nutritional strategy for managing obesity and its complications [9]. Cinnamon’s antiobesogenic effect may be related to its ability to induce thermogenesis in adipocytes as mediated by uncoupling protein 1 which is expressed in brown and beige tissues and improves metabolism to promote weight loss [100].

Moreover, cinnamaldehyde activates a classic thermogenesis pathway through protein kinase A signaling that phosphorylates p38 MAPK, inducing the transcription of thermogenic genes such as hormone-sensitive lipase and lipid droplet-associated protein perilipin 1 [52]. Additionally, as cinnamaldehyde is the primary natural agonist of the transient receptor potential ankyrin 1 (TRPA1), it may also indirectly influence food intake and weight gain, which can be expressed in gastrointestinal functions such as decreasing ghrelin secretion [101,102]. Other natural compounds present in cinnamon oil, such as cumin aldehyde (cumin), p-anisaldehyde (anise), and triglycaldehyde (onion/garlic), can activate human TRPA1 specifically but with lower affinity compared to cinnamaldehyde. Among these compounds, cumin aldehyde demonstrated glucose-dependent insulin secretagogue activity in diabetic rats by TRPA1 stimulation [102].

The AMPK pathway is also relevant to the study of obesity as it is a mediator of cellular energy production, which can improve insulin sensitivity in insulin-sensitive tissues, such as adipose tissue [103]. Cinnamon seems to exert beneficial effects via AMPK activation and enhanced adiponectin concentrations, as demonstrated by Kopp et al. [104]. They evaluated the Gi/Go-protein-coupled receptor 09A, which stimulates adiponectin secretion after binding trans-cinnamic acid from cinnamon.

Other protective effects ascribed to cinnamon appear to result from a reduction of hepatic expression of the transcription factor sterol regulatory element-binding protein-1c (SREBP-1c) and NF-κB, in conjunction with upregulation of PPAR-α, a cluster of differentiation 36 (CD36), fatty acid synthase, carnitine palmitoyltransferase I, and Nrf-2 [105]. Studies of obese rats with hepatic steatosis caused by a high-fat diet suggest enhancement of hepatic beta-oxidation and inhibition of hepatic lipogenesis, oxidative damage, and inflammation resulting from cinnamon intake.

Aqueous extract of Cinnamomum cassia bark has been linked to neurochemical and behavioral effects in rats by decreasing food intake through augmentation of 5-hydroxy tryptamine in the brain [106].

Only a few studies have reported a relationship between cinnamon and antiobesogenic effects in humans. Yazdanpanah et al. [107] have conducted a systematic review and meta-analysis to investigate the effects of cinnamon on fat and body mass, body mass index (BMI), waist circumference, and waist-hip ratio. In total, 21 randomized controlled trials (RCTs) with 1,480 participants were included, and it was reported that cinnamon supplementation decreased obesogenic parameters. In agreement with the studies discussed, a systematic review and dose-response meta-analysis suggested that cinnamon supplementation could improve obesity measures, particularly in obese subjects aged <50 years at dosages of ≥2 g/day for at least 12 weeks [108]. More recently, Keramati et al. [109] evaluated the effects of cinnamon on obesity rates in humans through an umbrella meta-analysis, which indicated that cinnamon supplementation reduced BMI. The effects of cinnamon were more pronounced at doses of ≥3 g/day and in patients with polycystic ovary syndrome. Table 4 [52,72,105,110–123] lists these associated experimental and clinical studies on the effects of cinnamon on obesity.

Table 4.

Studies involving cinnamon on obesity

Cinnamon and cardiovascular disease

Patients with CKD have a high risk of developing premature CVD due to a combination of traditional risk factors, including diabetes, obesity, dyslipidemia, hypertension, and a toxic uremic milieu [124]. Cinnamon may benefit cardiovascular health; indeed, studies have shown hypotensive effects, control of dyslipidemia, and protection of the endothelium and vascular smooth muscle cells (VSMC). As already discussed, cinnamon has anti-inflammatory and antioxidant properties, which can reduce the progress of atherosclerosis [56]. However, postulated hypotensive effects ascribed to cinnamon remain inconclusive [125]. Ghavami et al. [126] evaluated the effects of cinnamon supplementation on blood pressure through a systematic review and meta-analysis of RCTs. Eight studies, including 582 participants, suggested that cinnamon supplementation had beneficial effects only on diastolic blood pressure.

Components of cinnamon, such as catechin, epicatechin, procyanidin B2, and phenolic polymers, can act as agonists of PPARs, inhibiting the formation of advanced glycation end products to reduce oxidative stress and increasing the bioavailability of vasodilator NO [108,125].

Furthermore, cinnamon improves the lipid profile and reduces lipid oxidation and the risk of vascular blockage, mitigating potential hypertensive conditions [127]. Flavonoids and phenolic acids found in cinnamon inhibit pancreatic lipase, which is necessary for forming chylomicrons [110]. Cinnamon ameliorates lipid profiling by suppressing the expression of transcription factor SREBP-1c and liver X receptor alpha enzymes, such as ATP-citrate lyase and NF-κB p65. Furthermore, it upregulates PPAR-α expression to enable modulation of lipid metabolism [9]. Additionally, cinnamon has been reported to inhibit the secretion of proatherogenic apolipoprotein B 48 CD36, and the class A macrophage scavenger receptor, as well as the uptake of acetylated LDL, again suggesting that cinnamon can act as a preventive medicine [128,129].

Despite these promising results, the evidence remains inconclusive. Krittanawong et al. [130] have systematically reviewed the literature and evaluated cinnamon consumption and cardiovascular risk. A meta-analysis that included 23 studies (1,070 subjects) concluded that there was no association between cinnamon consumption and differences in LDL-cholesterol, high-density lipoprotein cholesterol, and HbA1c levels. Studies on cinnamon in vitro, in animals, and in humans are listed in Table 5 [9,45,131–144]. Again, allowance for different exposome features, such as microbiota composition, may be pertinent here [145].

Table 5.

Studies involving cinnamon on cardiovascular health

Does cinnamon benefit the gut microbiota?

Microbiota dysbiosis is a disruption to the normative microbial community driven by host-related exposome factors such as diet, resulting in perturbations to its composition and function [145,146]. Dysbiosis is associated with many chronic diseases, such as metabolic syndrome, inflammatory bowel disease, and CKD, which present a typical proinflammatory phenotype. Increased permeability in the gut with age and condition enables the entry of microbial metabolites, pathobionts, or endotoxins such as lipopolysaccharides (LPS) into the circulation [147,148]. It also presents a loss of symbiotic microbes.

Beyond typical treatments to mitigate dysbioses, such as pro-, pre-, or symbiotics, some bioactive compounds can be effective in modulating the gut microbiota [149,150]. Studies of the benefits of cinnamon in this capacity have been increasing [150,151].

Cinnamon compounds, such as polyphenols, reach the colon and serve as substrates for bacterial metabolism [152]. Normative gut microbiota is dominated by anaerobic bacteria from the Firmicutes and Bacteroidetes phyla. Dysbiosis is characterized by a loss of microbial diversity and symbionts and an increased representation of pathobionts [96,153]. Cinnamon effectively enriches gut microbiota by reducing Proteobacteria and increasing Bacteroidetes [154].

The essential oil in cinnamon contributes to the growth of salutogenic bacteria capable of short-chain fatty acid production. These can produce butyrate, acetate, and propionate, which not only serve as the substrate for the host cells but also regulate inflammation [154,155]. Cinnamon oil may improve microbiota diversity and downregulate inflammatory processes [154]. Moreover, cinnamon oil can protect against LPS-induced intestinal injury through upregulation of epidermal growth factor, claudin-1, occludin, alkaline phosphatase (ALP), and pregnane X receptor expression, improving gut barrier integrity [156]. The evidence supports cinnamon or cinnamon compounds as nutritional adjuvants for maintaining intestinal integrity [156,157].

An experimental study conducted with early-weaned rats, highly susceptible to intestinal stress and alterations, has shown that treatment with 100 or 200 mg/kg body weight/day cinnamaldehyde for 2 weeks improved the gut barrier and was accompanied by an increase in mucin production, reduced inflammation, and improved microbiome diversity [158]. These authors suggested that the beneficial effects were due to inhibition of NF-κB activation; upregulated expression of mucin 2, trefoil factor 3, and tight junction proteins; and reduced IL-6 and TNF-α expression, potentially mediated by increased in gut microbe diversity [158].

Another recent study has supported this assertion, indicating that the microbiota in ovariectomized mice displayed improved diversity after treatment with cinnamic acid. This result was accompanied by an elevation in transforming growth factor beta levels in bone marrow cells, which induced osteoblast differentiation and increased the expression of osteogenic markers [159].

Based on these data, cinnamon usage is encouraged not only to manage diseases influenced by microbiota, such as CKD but also for general health. The role of the microbiota in the health of the general population has recently been exemplified by a report linking poor renal function with accelerated aging and an imbalanced diet [160]. These data are pertinent to the treatment and management of CKD, as well as other diseases of aging.

Cinnamon: could it be of benefit in chronic kidney disease?

Although studies evaluating the effect of cinnamon on the kidneys are scarce, the salutogenic effects suggested by the literature (as shown in Fig. 2) suggest an overall benefit [161]. CKD is a significant cause of mortality globally, and its prevalence is growing in low-middle-income countries, where social deprivation amplifies its effects [145]. The reenvisioning of the Hippocratic concept of ‘food as medicine’ champions the use of natural bioactives as potential therapeutics to tackle the emerging diseasome of aging [12]. The use of cinnamon is merited for evaluation to be included in the physician’s and nutritionist’s armamentarium.

Figure 2.

The potential benefits of cinnamon to patients with diabetes, obesity, or CVDs.

Cinnamon can provide physiological benefits by mimicking insulin action through insulin receptor autophosphorylation of the β-subunit of tyrosine and promoting glucose transporter (GLUT) translocation via the 5' adenosine monophosphate-activated protein kinase (AMPK) signaling pathway. Cinnamaldehyde has antidiabetic activity through upregulation of the insulin signaling pathway, induction of peroxisome proliferator-activated receptors (PPARs), and inhibition of α-glucosidase and pancreatic α-amylase. Cinnamon may increase the expression of uncoupling protein 1 (UCP-1), promoting thermogenesis. It can also reduce hepatic expression of sterol regulatory element-binding protein-1c (SREBP-1c) and nuclear factor kappa B (NF-κB) and upregulate PPAR-α, fatty acid synthase, carnitine palmitoyltransferase I (CPT-1), and nuclear factor erythroid 2-related factor 2 (Nrf-2) to promote cytoprotective effects and reduce inflammation. Cinnamaldehyde might act as a natural agonist of transient receptor-ankyrin receptor 1 (TRPA1), reducing ghrelin secretion and food intake. Cinnamon may decrease SREBP-1 and cluster of differentiation 36 (CD36) expression and increase expression of PPAR-γ, reducing oxidative stress, inflammatory burden and, therefore, cardiovascular risk.

LXR-α, liver X receptor alpha; CVD, cardiovascular disease.

Common pathways underpin the salutogenic effects of cinnamon in CKD, including the inactivation of the ERK/JNK/p38 MAPK pathway leading to reduced renal interstitial fibroblast proliferation and hypertrophy [162]. Nrf2 pathway stimulation, promoting attenuation of renal damage and preservation of renal function, is also a key element in this mechanism [8,163–165]. Other reported benefits of cinnamon are the inhibition of peroxynitrite-induced nitration and lipid peroxidation and its influence on the production of NO and PGE2 [166,167].

Patients with CKD experience premature and accelerated aging [145], and cinnamon may also benefit in mitigating the effects of cellular aging. In support of this, it has been reported that cinnamaldehyde attenuates cellular senescence in the kidney through PI3K/AKT pathway-mediated autophagy via downregulation of microRNA-155 [168].

Cinnamon is a promising candidate in the dietetic management of CKD, as it can mitigate complications such as dyslipidemia and diabetes. Studies have suggested possible improvements in kidney function through dietetic approaches aimed at upregulating antioxidant and anti-inflammatory defenses [12,169]. However, despite the known properties of cinnamon, its effect on patients with CKD has not been explored, and most studies are experimental (Table 6) [65,168,170–173]. This highlights the need for further investigations.

Table 6.

Experimental studies involving cinnamon on kidney diseases

Toxicity caused by cinnamon

Contrary to popular belief, herbal medicines are not entirely safe and may have adverse effects. The available data suggest that cinnamon is safe for use as a spice, and moderate ingestion has several health benefits, as previously reported. However, its use for medicinal purposes in high doses or over a long duration may lead to adverse effects, such as gastrointestinal disturbances and self-limiting allergic reactions that should be clinically monitored [174]. Yun et al. [175] have reported that cinnamon extract (2 g/kg body weight/day for 13 weeks) might result in nephrotoxicity and hepatotoxicity in rats due to high doses of coumarin. In animals, despite all the extracts tested showing possible antioxidant activity in vitro, they showed acute dose-dependent toxicity (1,000, 2,000, 3,000, 4,000, and 5,000 mg/kg body weight) in vivo, with increased levels of aspartate transaminase, alanine transaminase ALP, urea, and creatinine reported in animals treated with the highest dose [57].

In a systematic review of the adverse effects of cinnamon, the authors report that most studies did not identify the cinnamon species responsible for these effects. Knowing that different cinnamon species contain other components, such as coumarin, studies on herbal medicines should be standardized to include their exact identification, dose, and duration of treatment [174]. Recently, Gu et al. [176] evaluated the safety of cinnamon in humans through a study using relevant meta-analyses and systematic reviews of RCTs and concluded that there are no adverse effects caused by cinnamon.

There is no exact recommendation for the daily intake of cinnamon. Still, studies recommend approximately 1 to 4 g per day, and attention should be paid to the amount of coumarin in different types of cinnamon and symptoms such as diarrhea, nausea, and vomiting [161].

Conclusion

Cinnamon compounds have several beneficial effects for consideration for inclusion in a ‘food as medicine’ strategy to treat CKD. These reside in inherent antioxidant, anti-inflammatory, cardioprotective, antiobesogenic, and antidiabetic properties. Additionally, they may reside in the ability of cinnamon to influence the composition of the gut and microbiota. Though most reported studies are preclinical, they indicate that human clinical studies are merited. Therefore, different clinical trials need to be planned regarding the dose and period of supplementation, the types of cinnamon species, and other populations. This review highlights the need for further studies on patients with CKD who suffers from several comorbidities, in which the use of cinnamon supplementation has demonstrated potential advantages.

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