Applied nutritional investigationPharmacokinetic study of amaranth extract in healthy humans: A randomized trial
Introduction
A diet rich in vegetables has been described as beneficial for longevity and overall health. The positive effects of vegetables may be attributed, in part, to inorganic nitrate (NO3ˉ), which is present abundantly in green leafy vegetables [1], [2]. To elicit any biological effects, NO3ˉ are likely to be converted to the nitrite (NO2ˉ) ion in the mouth via facultative anaerobic bacteria on the surface of the tongue [3]. When swallowed, NO2ˉ is further converted into nitric oxide (NO). The reduction of NO2ˉ to NO and other reactive nitrogen intermediates are facilitated in hypoxia [4]. The production of NO via nitric oxide synthase (NOS) is impaired in hypoxia and, thus, it has been proposed that the NO3ˉ → NO2ˉ → NO pathway represents a complementary system for NO generation across a wide range of redox states [5]. NO is an essential physiological signaling molecule with numerous functions in the body, including the regulation of blood flow, muscle contractility, glucose and calcium homeostasis, and mitochondrial respiration and biogenesis [6], [7].
There is now substantial evidence that dietary NO3ˉ supplementation can significantly increase the NO2ˉ level and reduce resting blood pressure in young adults [8], [9], [10], [11]. Moreover, dietary NO3ˉ supplementation may have positive effects on the physiological response to exercise [8], [12]. Supplementation with NaNO3 [12] or beetroot juice [13] resulted in a significant reduction in oxygen uptake during submaximal cycling. A recent placebo-controlled study reported that beetroot juice supplementation significantly reduced the oxygen cost of treadmill walking and improved exercise tolerance in healthy young adults [14]. These results are remarkable because the oxygen uptake and work rate relationship have traditionally been considered to be independent of age, health status, and aerobic fitness [15]. The reduction in the oxygen cost of moderate-intensity exercise after dietary NO3ˉ supplementation may be a result of a reduced adenosine triphosphate (ATP) cost of muscle force production [8], enhanced mitochondrial efficiency [16], or both. Dietary supplementation of NO2ˉ and NO3ˉ in mice has been shown to reverse endothelial dysfunction, suppress microvascular inflammation, and reduce levels of C-reactive protein in mice subjected to a high-cholesterol diet [17].
The availability of the NOS substrate l-arginine, and especially the NOS cofactor tetrahydrobiopterin, is lower in older age [18], which together with lower NO2ˉ, a sensitive marker of NOS activity, suggests that NO synthesis through the NOS → NO pathway might be impaired with the process of aging [19]. Additionally, superoxide (O2ˉ) production is increased with aging, which would lower NO bioavailability, given the rapid reaction between (O2ˉ) and NO to form peroxynitrite [20]. Given the positive association between NO and vascular health, these aging-related perturbations to NO metabolism might contribute to the endothelial dysfunction [21] and arterial hypertension [22] that develop with old age. Therefore, it is feasible that dietary NO3ˉ supplementation might enhance NO bioavailability and vascular function in older adults.
Leafy vegetables and roots/rhizomes of some edible plants are rich sources of dietary NO3ˉ. Amaranth (red spinach) is one such plant popularly grown as leafy vegetable in tropical regions of the world including Africa, India, Bangladesh, Sri Lanka, and the Caribbean. It is also grown as leafy vegetable through southeast Asia and Latin America. The leaves and grains of amaranth are edible and contain large amounts of NO3ˉ as well as other nutrients [23]. Amaranth leaves also are an excellent source of carotenoids, iron, calcium, ascorbic acid, and proteins [24]. Consuming leafy vegetables in large quantities as a daily diet may not be enough to produce significant levels of NO3ˉ and NO2ˉ in blood or to result in clinical benefits. In a recent clinical study with older adults, plasma NO3ˉ and NO2ˉ were increased by a high NO3ˉ supplement, but not by high NO3ˉ foods [25].
The purpose of the present study, therefore, was to assess whether oral intake of an NO3ˉ-rich dietary supplement (amaranth extract) is able to increase NO3ˉ and NO2ˉ levels in blood plasma and the saliva of healthy adults. The study was designed as a placebo-controlled, randomized, crossover study with 16 healthy adults.
Section snippets
Medicament
We used 2 g amaranth extract (Arjuna Natural Extracts Ltd., Aluva, Kerala, India) for the test, and 2 g of glucose (99.4% d-glucose) was used as placebo.
Participants
We screened 23 individuals. Of these, 16 healthy adult males (age 18–40 y) met the inclusion criteria and were selected for the study. Study protocol was explained to all the participants and they willingly signed a consent form to participate in the trial. The study was approved by the ethics committee of Good Society for Ethical Research,
Results
Sixteen individuals were recruited for the study. All completed the period 1 study, whereas one dropped out in the second period of study for unknown reasons. Ingestion of amaranth extract/glucose powder was tolerated well by all participants. None of the participants reported any discomfort or side effects.
Discussion
Nitric oxide is one of the most important signaling molecules produced within the body. The loss of NO generation because of endothelial dysfunction is one of the major causes of cardiovascular diseases [26]. Continuous generation of NO is essential for the integrity of the cardiovascular system [27]. The first pathway for the endogenous production of NO is through the oxidation of the guanidino nitrogen group of l-arginine (a semi-essential amino acid) by a group of enzymes called NOS
Conclusion
The results of this study clearly indicate that a single oral dose of amaranth extract is able to increase the levels of NO3ˉ and NO2ˉ in the body for at least 8 h. The increase in NO3ˉ and NO2ˉ levels can help in increasing the overall performance of people involved in vigorous physical activities or sports. Because NO deficiency is one of the reasons for endothelial dysfunction and disorders related to aging, amaranth extract may be beneficial for the elderly.
Acknowledgment
The authors acknowledge Arjuna Natural Extracts Ltd, Aluva, Kerala, India for providing the samples of amaranth extract (Oxystorm®).
References (34)
- et al.
Dietary nitrate: good or bad?
Nitric Oxide
(2010) Nitrite in nitric oxide biology: cause or consequence? A systems-based review
Free Radic Biol Med
(2006)- et al.
Emerging role of nitrite in human biology
Blood Cells Mol Dis
(2004) - et al.
Dietary inorganic nitrate improves mitochondrial efficiency in humans
Cell Metab
(2011) - et al.
Plasma nitrite reflects constitutive nitric oxide synthase activity in mammals
Free Radic Biol Med
(2003) - et al.
Plasma nitrate and nitrite are increased by a high-nitrate supplement but not by high-nitrate foods in older adults
Nutr Res
(2012) - et al.
Acute effect of high nitrate diet on brain perfusion in older adults
Nitric Oxide
(2011) - et al.
The role of nitrite in neurovascular coupling
Brain Res
(2011) - et al.
Mediterranean food and health: building human evidence
J Physiol Pharmacol
(2005) - et al.
Chemical generation of nitric oxide in the mouth from the enterosalivary circulation of dietary nitrate
Nat Med
(1995)
The nitrate-nitrite-nitric oxide pathway in physiology and therapeutics
Nat Rev Drug Discov
Nitric oxide regulation of mitochondrial oxygen consumption II: molecular mechanism and tissue physiology
Am J Physiol Cell Physiol
Dietary nitrate supplementation enhances muscle contractile efficiency during knee-extensor exercise in humans
J Appl Physiol (1985)
Effects of dietary nitrate on blood pressure in healthy volunteers
N Engl J Med
Acute and chronic effects of dietary nitrate supplementation on blood pressure and the physiological responses to moderate-intensity and incremental exercise
Am J Physiol Regul Integr Comp Physiol
Acute blood pressure lowering, vasoprotective, and antiplatelet properties of dietary nitrate via bioconversion to nitrite
Hypertension
Effects of dietary nitrate on oxygen cost during exercise
Acta Physiol (Oxf)
Cited by (20)
The importance and use of Amaranthus for crop diversification in the SADC region
2023, South African Journal of BotanyCitation Excerpt :Such findings reveal that amaranth can be utilised in fighting vitamin A deficiency and anaemia amongst children and lactating mothers in developing countries (Nawiri et al., 2013). Subramanian and Gupta (2016) also reported that oral administration of a 2 g single dose of amaranth extract increased the NO3− and NO2− levels in the body for at least 8 h when compared with a placebo group in a crossover design study. They further indicated that an increase in NO3− and NO2− levels could help to improve the overall performance of people involved in vigorous physical activities or sports.
Suitability of Amaranthus species for alleviating human dietary deficiencies
2018, South African Journal of BotanyCitation Excerpt :The vegetable intervenes in combating malnutrition and vitamin A deficiencies in children (Bulux et al., 1994; Tang, 1998) and recommended as one of the most effective and sustainable way of supplementing dietary systems and curbing nutrient deficiencies (Nawiri et al., 2013). Recent research undertaken by Subramanian and Gupta (2016) concluded that oral intake of amaranth extracts is able to increase the levels of nitrate (NO3−) and nitrite (NO2−) in the body for a minimum of 8 h. This was because the rich dietary supplement offered by amaranth increases nitrite and nitrate concentrations in the saliva and blood plasma of healthy adults.
Safety Evaluation of Amaranth Extract by Acute, Sub-Chronic and Chronic Exposure in Rats
2023, Biomedical and Pharmacology JournalThe nutraceutical properties and health benefits of pseudocereals: a comprehensive treatise
2023, Critical Reviews in Food Science and NutritionAmaranth, quinoa and chia bioactive peptides: a comprehensive review on three ancient grains and their potential role in management and prevention of Type 2 diabetes
2022, Critical Reviews in Food Science and Nutrition
The authors participated equally in the conception and design of the study; generation, collection, assembly, analysis and/or interpretation of data; drafting the manuscript; and approval of the final version of the manuscript. The authors have no conflicts of interest to declare.