Introduction
Functional Compounds in Beetroot
Beetroot Effects on Endothelial Function
The Effects of Beetroot on Blood Pressure and Vascular Function
The Effect of Beetroot on Glucose and Insulin Homeostasis
The Effect of Beetroot on the Microbiome
References
Further Reading
Beetroot is a nitrate-rich root vegetable. Research has demonstrated that the consumption of nitrates from sources such as beetroot, carrots, and turnips, may increase the body's available nitric oxide, a key regulator of vasodilation, which could produce long-term effects on lowering blood pressure.
Beetroots. Image Credit: Ulada/Shutterstock.com
Ingested nitrates are metabolized to produce nitrates by enteral bacteria, and are subsequently reabsorbed by the intestines.
Functional compounds in beetroot
Beetroot consists of several biologically active phytochemicals. These include betalains (which comprise ~ 70–100% of the phenolic content of beetroot) such as betacyanins and betaxanthins, polyphenols, flavonoids, inorganic nitrate (NO3), and saponins.
Beetroot is also a rich source of minerals such as potassium, phosphorous, calcium, magnesium, copper, sodium, iron, zinc, and manganese. It is also considered to be a potent source of vitamin C.
Beetroot is classified as one of the ten plants with the highest antioxidant activity. This antioxidant activity is attributed to its high phenolic content. Phenolic compounds can function as antioxidants in several ways. The hydroxyl groups function as hydrogen donors which can react with reactive oxygen and nitrogen species to terminate the production of new radicals, subsequently breaking the cycle of new radical generation.
The antioxidant function of phenolic compounds is also attributed to the metal ion chelation; these are also implicated in the production of free radicals. Moreover, phenolic structures can interact with and inhibit proteins, namely enzymes, involved in radical generation. These include cytochrome P450 isoforms, cyclooxygenases, xanthine oxidases, and lipoxygenases.
Beetroot effects on endothelial function
This improvement in endothelium function is attributed to its high, biologically safe nitrate concentration. Although nitrate is an inert compound, it transforms into nitrite and nitrogen oxide due to activity in the oral cavity.
Nitrogen oxide (NO) is known to have a vasodilatory effect, which consequently causes a reduction in blood pressure and increased delivery of oxygen and nutrients to active muscle.
Beetroot is highly sought after for this reason as biologically safe nitrate is difficult to prepare. Nitrate-rich beetroot supplements, prepared through methods such as freeze-drying to prolong shelf life and maintain biological activity, have recently entered the market. Among them, pseudoplastic beetroot gels and beetroot chips are the most recently formulated functional forms of beetroot supplements.
Beetroot is also considered to be high in oxalic acid, containing 94.6–141.6 mg/100 g. Oxalic acid is a metal ion chelator and promotes the formation of nephroliths (kidney stones), and so is considered to be a health concern in patients predisposed to kidney dysfunction.
The effects of beetroot on blood pressure and vascular function
The functional effect of beetroot on blood pressure has been demonstrated in a study of 72 hypertensive patients. Half of the patients ingested 250 mL of beetroot juice once daily and the other half who were administered a nitrate-free beetroot juice placebo. Sustained reductions of 7.7 mm Hg in systolic pressure and 5.2 mm Hg in diastolic pressure were observed over 24 hours.
This effect is similar to the average blood pressure drop observed with a single antihypertensive treatment (9.1 mm Hg in systolic pressure/5.5 mm Hg in diastolic pressure). Beetroot was also found to produce an ∼20% improvement in endothelial function.
Several other studies have corroborated this finding, emphasizing the blood pressure-lowering properties of beetroot in normal and hypertensive individuals across various health states. The nitrate to nitrite pathway is predominantly the cause of such effects; however, other bioactive compounds (i.e., betacyanins) contribute to the positive effects on blood pressure and vascular function.
NO also results in a decrease in reactive oxygen species (ROS) production, which subsequently improves endothelial function. This decrease in ROS, with an upregulation in the activity of antioxidant enzymes, subsequently results in a reduction in oxidative stress.
NO also promotes renal function through the activation of the Soluble Guanylate Cyclase-cyclic guanosine monophosphate (SGC-cGMP) pathway which results in a decrease in renovascular resistance, subsequently promoting renal function.
Renal function is also promoted through the direct effect of NO on the angiotensin II type I receptor gene expression. This promotes the production of the compound NO2- S-nitrosothiol, reducing the concentration of Nicotinamide Adenine Dinucleotide Phosphate (NADPH) oxidase activity, improving renal blood flow and vascular relaxation and altering water retention.
Compounds such as betalains and polyphenols can suppress cyclooxygenase-2, an enzyme that mediates the inflammatory response and reduces NF-κB, an activator of inflammatory T cells. This serves to reduce inflammatory markers and improve the function of the endothelium which results in reducing blood pressure.
Blood pressure. Image Credit: Chompoo Suriyo/Shutterstock.com
The effect of beetroot on glucose and insulin homeostasis
Beetroot has a potential hypoglycemic effect. Several studies have shown a significant reduction in blood glucose level, as well as an improved glycemic and insulin response.
Polyphenols, flavonoids, nitrates, and other bioactive compounds are critical in mediating this effect. In addition to lowering blood sugar on controlling the glycemic response, some studies have indicated a favorable effect on lipid profile.
The effect of beetroot on the microbiome
The consumption of beetroot juice is associated with the abundance of certain species of bacteria in the mouth and a decrease in bacteria associated with inflammation and diarrhea.
Researchers hypothesize that a healthy oral microbiome sustained over a long period could serve to slow down negative cognitive and vascular alterations that are correlated with increased age.
There are several health-promoting characteristics of beetroot and its downstream metabolic products. The compounds serve as potential treatments for disorders associated with the metabolism including diabetes, hypertension, insulin resistance, and kidney dysfunction.
Several studies support the systolic and diastolic blood pressure reducing properties of beetroot, alongside its ability to inhibit platelet aggregation and improve endothelial and vascular function.
Moreover, studies have conclusively reported the ability of beetroot to reduce blood glucose and improve insulin homeostasis. Finally, studies support the reno-protective effect of beetroot. These effects are attributed to its high concentration of phytochemicals, alongside several other compounds and essential nutrients. Most poignantly, beetroot is abundant in inorganic nitrate - a key mediator of these effects.
References
- Clifford T, Howatson G, West DJ, et al. (2015) The potential benefits of red beetroot supplementation in health and disease. Nutrients. doi:10.3390/nu704280.
- Mirmiran P, Houshialsadat Z, Gaeini Z, et al. (2020) Functional properties of beetroot (Beta vulgaris) in management of cardio-metabolic diseases. Nutr Metab (Lond). doi:10.1186/s12986-019-0421-0.
- Zamani H, de Joode MEJR, Hossein IJ, et al. (2021)The benefits and risks of beetroot juice consumption: a systematic review. Crit Rev Food Sci Nutr. doi:10.1080/10408398.2020.1746629.
- Mirmiran P, Houshialsadat Z, Gaeini Z, et al. (2020) Functional properties of beetroot (Beta vulgaris) in management of cardio-metabolic diseases. Nutr Metab (Lond). doi:10.1186/s12986-019-0421-0.
Further Reading
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