Oxidative stress plays a major role in the pathogenesis and progression of diabetes and CVD [22]. Furthermore, functional
foods with an antioxidant effect have been reported to repress oxidative stress [22], and positively associated with BP-lowering potential. Hyperglycemia causes the auto-oxidation of glucose, glycation of proteins, and the activation of polyol metabolism; cinnamon has been reported to improve the antioxidant status of patients with metabolic syndrome [23]. Previous studies also demonstrated that plasma melondialdehyde levels were reduced by an aqueous extract of cinnamon, indicating decreased lipid peroxidation [23]. This could be linked with BP regulation. According to Wainstein et al [15], it has been proposed that cinnamon may exert its beneficial effects via activation of peroxisome proliferator-activator receptors and inhibition of advanced glycation end-product formation. Several phenolic compounds found in cinnamon such as catechin, epicatechin, procyanidin B2, and phenol polymers, showed significant inhibitory effects on the formation of advanced glycation end products [21]. Cinnamon also has been shown to reduce both glucose and SBP in rodent studies [17]. Moreover, cinnamon could be included with low-carbohydrate ketogenic diets (LCKD) to improve glycemia and BP, as LCKD showed positive effects on HbA1c, body weight, waist circumference, serum triglycerides, and glycemic control in participants with T2DM [24]. However, patients with diabetes on a combination of ketogenic and cinnamon diet should be under strict medical supervision because of its higher blood glucose–lowering potential. Most importantly, not all clinical trials have shown positive effects of cinnamon on glycemic and BP regulation, and the type and amount of cinnamon, as well as the type of individual and the type of medication taken concurrently, are likely to affect the response to cinnamon [21]. One of the key limitations of this meta-analysis is that it is based on a small number of RCTs. Consequently, our meta-analysis may be under powered to detect statistically significant difference in many end points. Therefore, the small number of clinical trials and low population numbers do not allow a definitive conclusion to be drawn regarding the efficacy of cinnamon as a treatment for hypertension, and may raise expectations in terms of potential usefulness of cinnamon in BP control, which seem unjustified given the limited evidence to date.We have already observed many promising results in the field of nutritional supplements and cardiometabolic health, which however has been rarely supported by large, properly designed clinical trials. Therefore, there is a need to use caution in the interpretation of promising findings from very limited trial evidence, as in this context. Nevertheless, we hope to revisit this question in the future when there is more research data and enough power available to prove the long-term tolerability and efficacy of cinnamon on BP control.