An estimated 22% of adults the world over exhibit raised blood pressure (WHO 2014), and systemic hypertension remains the largest attributable risk factor for mortality worldwide – tendency increasing (Kapil et al. 2015).
On the brighter side: recent studies provide compelling evidence that ingestion of beetroot (Beta vulgaris rubra, red beetroot) offers beneficial physiological effects that may translate to improved clinical outcomes for pathologies such as hypertension (high blood pressure), atherosclerosis, type 2 diabetes, and dementia. Beetroot positively influences the cardiovascular system. Regarding hypertension, numerous studies showed beetroot significantly reduced systolic and diastolic blood pressure (Box 1) when delivered acutely as a juice or in bread (Clifford et al. 2015).
What’s In a Beet?
Apart from high levels of inorganic nitrate, NO3–, beetroot contains several potent phytochemical compounds: ascorbic acid (vitamin C), vitamin A, vitamin B6, flavonoids, carotenoids, phenolic acids, and betalains, a group of red-violet or yellow-orange pigments with strong antioxidant and anti-inflammatory properties (Ninfali & Angelino 2013). This has sparked interest to research possible roles for beetroot in pathologies characterised by chronic inflammation and oxidative stress (see Box 2), such as liver disease, arthritis, and cancer (Clifford et a. 2015). Other identified antioxidants from beetroot include epica techin, rutin and caffeic acid. It also contains sugar, potassium, magnesium, folic acid, iron, zinc, calcium, phosphorus, sodium, niacin, biotin, and soluble fibre (Wootton-Beard & Ryan 2011, Crocker 2008).
How Does it Work?
To understand how beetroot exerts its positive effects, let’s visit some biochemistry relevant to good vascular health (i.e. happy blood vessels). Nitric oxide, NO, is an important messenger molecule that modulates a vast number of physiological processes, ranging from vasodilation, muscle contractility, and immune function to neurotransmission and memory (Wylie et al. 2013, Weitzberg et al. 2010). The endothelium (inner lining of blood vessels) uses it to signal the surrounding muscle tissue to relax, leading to dilated blood vessels and increased blood flow. People suffering from cardiovascular disease, including high blood pressure, usually exhibit diminished NO levels (Kapil et al. 2015). Thus, one would think anything delivering NO to blood vessels may alleviate symptoms. This is only partly correct, however. Using NO from organic molecules like nitroglycerin showed benefit, and also complications (Kapil et al. 2015). But what about NO derived from inorganic sources (Box 3)?
Since some vegetables (e.g. beetroot, spinach, lettuce) contain high amounts of (inorganic) nitrate, several researchers investigated the possibility that the well-established beneficial effects of a diet rich in vegetables on cardiovascular diseasemay in part be due to nitrates (Weitzberg et al. 2010, Webb et al. 2008). Indeed, use of inorganic nitrate has a long medical history: an 8th Century Chinese manuscript uncovered at the Buddhist grotto of Dunhuang advises administering nitre (KNO3) sublingually to relieve angina pectoris (Butler & Feelisch 2008). Placement under the tongue proved crucial to achieve pain relief (see why below). Potassium nitrate served as a diuretic for oedema since the 16th century and different nitrate salts were in use until the mid-1930s, when alternative diuretics became available (Lidder & Webb 2012). The idea that inorganic nitrates exert beneficial effects on high blood pressure patients through conversion to nitrite was postulated over 80 years ago, and more recently also confirmed for healthy people (Coles et al. 2012, Kapil et al. 2010, Webb et al. 2008).
So, let’s look at beetroot in particular. It contains high levels of bioavailable inorganic nitrate, NO3– (250 mg/kg fresh weight). The short version is that ingesting beetroot delivers nitrate derived NO to blood vessels, causing dilation, and lowering blood pressure by up to 10 units over a 24h period, with greatest impact ~3h after drinking the juice (Webb et al. 2008).
In more detail, the body has two ways to provide NO: from endogenous reactions, and through the food supply. After a meal rich in nitrate, the small intestine rapidly absorbs it, with blood plasma nitrate levels greatly increasing and remaining elevated for hours (Presley et al. 2011, Lundberg et al. 2008). Plasma nitrite (NO2–) levels also increase after nitrate ingestion, albeit slower (Webb et al. 2008). Although most nitrate is excreted with urine, up to 25% make its way to the salivary glands with subsequent exposure to tongue bacteria in the oral cavity (Weitzberg et al. 2010). Remember the Chinese manuscript advising people to put nitrate (as KNO3) under their tongue? Tongue bacteria reduce nitrate to nitrite – a crucial step, as mammals cannot effectively metabolize NO3–, relying on symbiotic oral and gut bacteria instead (Lundberg et al. 2008). Upon swallowing saliva, nitrite enters the stomach and circulation, where enzymes convert it to NO, resulting in vasodilation and significant blood pressure lowering (Kapil et al. 2015). Note that regular use of antiseptic mouthwash may diminish tongue bacteria, and with them the oral nitrate – nitrite conversion (Clifford et al. 2015). Indeed, mouthwash use has been correlated with increased blood pressure in rats and humans (Habermeyer et al. 2015). All up, about 5% of a swallowed nitrate portion convert to nitrite (Bryan & Ivy 2015).
This reductive pathway from nitrate to nitrite and then NO has also been demonstrated in the stomach, on the skin surface, and in urine (Lundberg et al. 2008). In addition, presence of vitamin C and polyphenols (reducing compounds), as readily available from fresh foods, greatly enhances nitrite reduction to NO (Lundberg et al. 2008).
Beetroot’s beneficial effects on the cardiovascular system are largely attributed to its high nitrate content.
(The following discusses nitrate. Given that positive effects of beetroot are largely attributed to nitrate and that it may underlie the recognized health benefits of a vegetarian diet, I thought an understanding of nitrate important. You can skip ahead to reading more about beetroot use and benefits though…)
But Wait, I Thought Nitrate Was Harmful?
On the whole, nitrate is subject to ongoing scientific debate, without consensus for the last 50 years (Powlson et al. 2008). When reading the literature, there seem to be two factions: one advocating for rethinking nitrate (in terms of recommended limits and actual health applications), and one pointing out its potential dangers (as evidenced mostly by animal studies), thus calling for more research before changing safety levels (Grinsven et al. 2006).
Nitrate and Public Perception
Public perception of nitrate leans toward the negative rather than the positive. Butler & Feelisch (2008) give a good account for the reasons: “The driving force for this development appears to have been the fear fostered by discussions, in both the lay press and scientific literature, about the purported health risks of exposure to nitrite and nitrate. Reports about methemoglobinemia [when nitrite reacts with hemoglobin, resulting in methemoglobin which cannot carry oxygen] in infants caused by drinks or food prepared with nitrate-rich (and bacterially contaminated) well water and vegetables such as spinach, celery, and carrots (“blue baby syndrome”), intentional and occupational intoxications in adults, increasing nitrate levels in soil and lakes as a result of fertilizer overuse, and the formation of potentially carcinogenic N-nitrosamines all contributed to the negative image that nitrite and nitrate have held in recent years. As a result, major efforts have been made to remove as much nitrite and nitrate as possible from our drinking water, to advocate replacement of nitrite by other (often less effective) food preservatives, and to establish cultivation conditions that result in crops with reduced levels of nitrate. Although possible long-term consequences of a chronically reduced intake of nitrite and nitrate on human health are unknown, doubts have been raised about the general health risk of nitrite/nitrate intake. […] Despite the critical voices, the image of nitrite and nitrate remains stigmatized.”
Concern about nitrate primarily stems from cases of infant methemoglobinemia and a possible link to cancers of the digestive tract (Powlson 2008).
Nitrate and Cancer
While neither nitrate nor nitrite act as direct carcinogens, nitrite derived from dietary nitrate may react with dietary amines to form carcinogenic nitrosamines. Since 1973, about 50 epidemiological studies researching the link between nitrate and stomach cancer incidence failed to show a convincing link (Powlson et al 2008, Lidder & Webb 2012). Some studies even reported a lowered cancer rate associated with high nitrate intake (Björne et al. 2004), and, as we shall see, many investigators report beneficial effects of dietary nitrate. The European Food Safety Authority sums it up such: “Epidemiological studies do not suggest that nitrate intake from diet or drinking water is associated with increased cancer risk. Evidence that high intake of nitrite might beassociated with increased cancer risk is equivocal” (EFSA 2008). With the exception of tobacco-specific nitrosamines, the evidence for carcinogenity of N-nitroso compounds in humans remains inconclusive, even though a 2012 review firmly concluded there was no association between nitrosamine formation in humans and gastric cancer (Butler 2015). But prospective cohort studies suggest an association of red meat and nitrite-preserved meat intake with an increased risk for colon cancer and chronic lung disease (Habermeyer et al. 2015, Hord et al. 2009). (Sodium nitrite serves as colorant, flavor enhancer, and antimicrobial agent in cured and processed meats, including bacon, bologna, corned beef, hot dogs, luncheon meats, sausages, and canned and cured meat and hams.)
The Netherlands Cohort Study tracked 120,000 men and women for 16.3 years and concluded that, although nitrosamines in the diet may cause oesophageal carcinomas, there was no clear association with other gastric subtypes (Butler 2015). All up, the evidence for a cancer causing role of nitrate and nitrite in humans is inconsistent (Milkowski et al. 2009).
Nitrate and Water
Drinking water contains variable amounts of nitrate, deriving from bacterial nitrogen fixation and breakdown of organic compounds in the soil. The nitrate amount permitted in water is regulated in Europe (50 mg/l) and the US (44 mg/l), beginning in the 1940’s, after noticing an apparent connection between infantmethemoglobinemia and well water containing high nitrate levels. Consequently, the EPA (US Environmental Protection Agency) set a maximum contaminant level for nitrate of 10 mg/l (nitrate nitrogen (NO3-N); multiply by 4.42 to give above 44 mg/l, referring to the NO3– ion), last revised in 2002 (EPA 2007). However, in 1948, experiments with babies (!) revealed nitrate levels as an unlikely cause of infant methemoglobinemia, but rather that exposure to fecal bacteria (from well water) and subsequent intestinal infections caused the condition (Powlson et al. 2008). Indeed, methemoglobinemia is highly unlikely in the absence of contaminating bacteria, as these are mandatory to convert nitrate to nitrite in order for raised nitrite levels to affect an infant(Lidder & Webb 2012).
That said, the cumulative environmental burden of nitrate from fertilizer use and large-scale livestock production (nitrate rich manure) may cause major changes to terrestrial and aquatic ecosystems, potentially affecting their biodiversity and species abundance, with knock-on effects for humans (Powlson et al. 2008, Grinsven et al. 2006). Examples include nitrate runoff to rivers and lakes causing excessive growth of algae and associated anoxia (diminished oxygen levels) in coastal and estuarine waters, and groundwater contamination (Katan 2009).
What about dietary nitrate concentrations?
Nitrate and Diet
The World Health Organisation (WHO) first recommended an upper level for dietary nitrate in 1962: the ADI (acceptable daily intake) for nitrate is 0–3.7 mg/kg (WHO Food Additive Series 50). It still stands today and equates up to 259 mg of nitrate for a 70 kg adult (or ~4.2 mmol). The ADI was based on a brief FDA (US Food and Drug Administration) report testing rats and two dogs on sodium nitrate. The WHO took these findings and calculated that a dose of ?500 mg sodium nitrate/kg body weight was harmless to rats and dogs (Katan 2009). Dividing that result by 100, they arrived at the current ADI for human nitrate consumption, either given as 5 mg/kg sodium nitrate, or as 3.7 mg/kg NO3– (equating 0.06 mmol NO3– ).
Despite being a major source of nitrate, increased consumption of vegetables is widely recommended because of their generally agreed beneficial effects for health (EFSA 2008). Some even suggest the well recognized, health-promoting effects of the Mediterranean diet might in part be due to nitrate (Butler & Feelisch 2008).
A vegetarian diet contains ~4.3 mmol nitrate per day, close to the ADI, but almost four times more than a “normal” diet at ~1.2 mmol (Lidder & Webb 2012). A relatively large range of nitrate dosing has been studied in humans and mice, showing clear therapeutic benefit without any signs of toxicity (Bryan & Ivy 2015). Indeed, acute nitrate ingestion (e.g. beetroot juice) may well exceed the suggested ADI (Lidder & Webb 2012, Lansley et al. 2011), seemingly without harmful consequences (Butler 2015), but a host of beneficial ones:
- nitrate derived NO inhibits blood platelet adhesion and aggregation (Lidder & Webb 2012),
- lowers blood pressure (Kapil et al. 2015),
- reduces oxygen cost of exercise (Lansley et al. 2011),
- improves intestine health (Björne et al. 2004),
- preserves or improves endothelial dysfunction (Webb et al. 2008),
- enhances exercise performance in healthy individuals and patients with peripheral arterial disease (Lidder & Webb 2012),
- has anti-inflammatory properties (Ninfali & Angelino 2013),
- from 2001, nitrite was discovered to provide an important alternative source of nitric oxide (NO), particularly at reduced oxygen levels (Liddder & Webb 2012),
- nitrite protects mitochondria by drecreasing the production of oxygen radicals (Weitzberg et al. 2010),
- nitrite accelerates wound healing through exerting antibacterial effects (Butler & Feelisch 2008),
- nitrite may increase cerebral blood flow in hypoxic areas and sustain cognitive function (Presley et al. 2011).
The body self-regulates its nitrate levels, excreting excess when exposed to high loads of dietary nitrates (Lidder & Webb 2012) – you may find beetroot colors urine and stool (beeturia) (Presley et al. 2011).
Foods high in nitrate (>1g/kg), in descending order: rocket, spinach, lettuce, radish, beetroot, Chinese cabbage; plants with medium nitrate levels (<1g/kg): turnip, cabbage, green beans, leek, spring onion, cucumber, carrot, potato, garlic, peppers (Lidder & Webb 2012). Also interesting to note: not all plant parts contain equal amounts of nitrate. Generally, leaves exhibit higher amounts than stems > roots > fruit > seeds. Plant nitrate content depends on genotype, soil quality, fertilizer use, storage conditions, among other factors (Hord et al. 2009).
So What to Make of It?
Given the evidence, consuming increasing amounts of vegetables is associated with a reduced risk of cardiovascular disease and increased longevity. A report by the World Cancer Research Fund assessing the impact of food, nutrition, and physical activity on incidence of cancer showed no link of vegetable intake with increased cancer (Kapil et al. 2011). Indeed, all evidence points to the contrary. Similarly, evidence linking inorganic nitrate ingestion to increased incidence of cancer is weak (Katan 2009).
Butler & Feelisch (2008) also offer a good point regarding nitrite causing cancers of the digestive tract: “Interestingly, the average dietary intake of nitrate roughly equals that produced by the endogenous production of NO. Thus, if nitrite truly were of concern to human health because of its propensity to form carcinogenic nitrosamines, then the human body would have a significant evolutionary design flaw because c. 5% of all ingested and endogenously produced nitrate eventually ends up as nitrite in the stomach.”
Weitzberg et al. (2010) express their view on nitrate like this: “The nutritional implications of nitrate and nitrite biology are exciting. The amounts of these anions needed for the effects on the cardiovascular system […] are readily achieved by our everyday diet. Future studies will elucidate whether the cardiovascular benefits of a diet rich in vegetables, such as the Mediterranean diet, are related to nitrate. If that is the case, we may have to reconsider our current thinking, and what is presently considered a harmful constituent may in the future be regarded as an essential nutrient”.
Five years later, Bryan & Ivy (2015) concur with the nutrient view, adding to previous evidence that nitrate/ nitrite exert beneficial effects at levels exceeding current recommended limits (Hord et al. 2009). And as said before, salivary nitrate levels may indeed rise above many times the acceptable daily intake limit after beetroot ingestion (Tamme et al. 2010, Lundberg et al. 2008) or consuming high amounts of other nitrate rich vegetables (Habermeyer et al. 2015, Gilchrist et al. 2010). Regular, prolonged daily beetroot juice consumption is tolerated well (Kapil et al. 2015) and evidence for carcinogenic effects of dietary nitrate/ nitrite is inconsistent(Bryan & Ivy 2015, Gilchrist et al. 2010). If typical consumption patterns of vegetables and fruits exceed regulatory limits – beetroot juice or a portion of spinach consumed in one serving of salad can exceed the ADI – the value of such a guideline becomes questionable (Bryan & Ivy 2015, Hord et al. 2009).
Given the long time it takes for new basic science discoveries to take root and translate into well established practice – about 17 years – perhaps it’s time to reconsider nitrate, now. While I’m not for changing (raising) environmental nitrate/ nitrite limits, I do think our body’s innate intelligence handles elevated dietarynitrate/nitrite levels, as resulting from beetroot and other vegetable intake, by itself (see Webb et al. 2008 for images showing nitrate ingestion and its subsequent fate in the body). Indeed, nitrate participates in so many physiological processes, that it cannot be simply dismissed as an unwanted toxin (Carlström et al. 2010, Hord et al. 2009). Rather, the body requires correct amounts to function properly, reabsorbing nitrate through the kidneys (an estimated 96%) and also producing its own. Paracelsus probably had it right in saying: ”Dose makes the poison” (Bryan & Ivy 2015).
I regularly add beetroot to my daily vegetable juice, no worries. Of course, under clinical considerations, the situation for a hypertensive person may be different. That said, Kapil et al. (2015) postulate that the blood pressure lowering effects seen in patients with mild hypertension may be greater in patients with more severe hypertension, a sentiment shared by others: “This therefore holds promise that dietary nitrate will be more effective in reducing blood pressure [BP] when it is needed, i.e. in people with high normal BP or hypertension, and results of dietary nitrate in hypertensives are awaited. Similarly, dietary nitrate would appear not to induce unwanted hypotension [low blood pressure] in people with low normal BP. The enterosalivary circulation also provides an inherent limiting mechanism to prevent excessive conversion of nitrate to nitrite, avoiding the risk of nitrite toxicity” (Lidder & Webb 2012, Webb et al. 2008).
The awaited results alluded to are now available from Kapil et al. (2015), who provide the first clinical evidence “of durable blood pressure reduction with dietary nitrate supplementation [beetroot juice] in a relevant patient group”.
How Much Beetroot Should I Ingest? In What Form?
Choosing the right amounts can be tricky. Research revealed that polyphenols and antioxidant capacityof beetroot were higher in biodynamic and integrated farming systems compared to conventional farming (Ninfali & Angelino 2013) and an Austrian study showed that beetroot products by different manufacturers also vary widely in their nitrate content. Wruss et al. (2015) tested 16 commercial juices, four beetroot powders and freshly prepared juice from seven different beet varieties. Nitrate content diverged by a factor of 10 between freshly pressed juices (approx. range 0.56 – 4.6 g/l) and a factor of up to 240 between commercial juices and powders (range 0.01 – 2.4 g/l). With the exception of one beet variety (Robuschka), freshly made juices contained significantly higher nitrate levels (an average of 1970 mg/l, corresponding to about 985 mg/kg fresh weight) compared to commercial juices. This seems to speak for getting a juicer and starting growing beets. =) At least for reading labels and thus making wiser choices. Apart from the volume used, the actual nitrate concentration matters to accurately determine your intake. It should be printed on the label or be available from the manufacturer. With the information given here, you should be equipped to determine best juice volumes for a given product (Box 4). Let’s take a look at what beetroot juice volumes and concentrations different studies applied to measure any effects.
Webb et al. (2008) used organic beetroot juice to study the effect on blood pressure in healthy volunteers. Participants drank 500 ml of either beetroot juice (0.3 mmol nitrate/ kg) or water, with repeated blood pressure readings taken over the next 24 hours. Within three hours of ingestion, a reduction in both systolic (10 mm Hg) and diastolic blood pressure (8 mm Hg) was noted, with the effect still present 24h after a single administration. Subsequently, the same group used 250 ml (5.5 mmol nitrate) of organic beetroot juice in healthy volunteers, observing similar effects (Kapil et al. 2010). Wylie et al. (2013) tested organic beetroot juice supplementation in healthy volunteers to observe similar results at 140 ml and 280 ml volumes (equating ~ 8.4 and 16.8 mmol of nitrate content).
Zamani et al. (2014) tested obese, hypertensive heart failure patients (>56 years of age) on stable medication for improved exercise capacity under the influence of a single organic beetroot juice administration (140 ml, 12.9 mmol nitrate). Their data suggest that NO3– improved exercise capacity in study participants by elevating peak oxygen uptake and delivering more oxygen to exercising muscles.
Another beetroot juice supplementation study in older adults provided two drinks per day (816 mg total nitrate) to observe an increase in plasma nitrite concentration, reduced blood pressure, and positive physiological responses to exercise. Nitrate supplementation at a dose of 6.62 mg/kg can also enhance exercise performance in patients with peripheral artery disease (Bryan & Ivy 2015).
One UK company developed a 70 ml organic beetroot shot that Wootton-Beard & Ryan (2011) found to be a potent deliverer of antioxidants and polyphenols. Other companies also created beetroot shots and sports drinks with high nitrate content (e.g. 240 mg/ 60 ml serving) (see Wruss et al. 2015).
A recent double-blind, placebo controlled clinical trial offering hypertensive patients 250 ml(~6.4 mmol nitrate) of organic beetroot juice daily for four weeks showed a sustained and significant reduction of blood pressure (Kapil et al 2015). Endothelial function also improved by c. 20% and arterial stiffness was reduced. Patients tolerated the intervention well, with no signs of tachyphylaxis or induced endothelial dysfunction, contrary to other NO interventions using organic nitrates (e.g. nitroglycerin) (Kapil et al. 2015, Lidder & Webb 2012). The researchers conclude: ”This is the first evidence of durable blood pressure reduction with dietary nitrate supplementation in a relevant patient group. These findings suggest a role for dietary nitrate as an affordable, readily available, adjunctive treatment in the management of hypertensive patients”. Out of all references, this would be the one to take to your healthcare practitioner to discuss your “beetroot options”. It presents exciting results. Bring them to your doctor’s attention!
The daily amount of inorganic nitrate from beetroot juice consumed in above studies ranged from 5.5 to 18.4 mmol/ dose, corresponding to 341 – 1141 mg nitrate and about 132 – 440% of the ADI value for a 70 kg adult, respectively.
Given the reported range of tested concentrations and volumes, it seems 200 – 400 mg of nitrate a day may suffice. Tamme et al. (2010) recommend a daily mean beetroot juice intake of 150 ml, going from dietitian’s guidelines. Alternatively, a 60 ml beetroot shot might do the trick, too. Personally, rather than dealing with figures and calculations, I just press fresh juice from homegrown/ organic beets. I add some beetroot almost every day, mixed in with greens, carrots, apples, whatever floats around the kitchen. Below recipe came out of what I had left one day and trying to create a palatable concoction regardless, leading to one of my favorite drinks. =) As seen, fresh juices may contain a higher dose of nitrate than mentioned above (>>560 mg/l). So far, I have felt no repercussions from adding beetroot frequently.
Above thoughts refer to healthy people intending to stay that way. Athletes seeking to improve performance (see also below) should ingest a minimum of 500 ml beetroot juice (450-550 mg nitrate) at least 2.5h before exercise to allow sufficient time for nitrite formation (Bryan & Ivy 2015). To use beetroot for blood pressure management, involve your doctor to set the appropriate dose for you and to monitor effects. As age, gender, weight and any present health conditions all play into this, giving a ball park figure for beetroot as a treatment is inappropriate here. Rather, everyone needs to decide what is best for their specific circumstances. Cited studies may provide guidance for determining the amount of beetroot per day for medicinal purposes. Possible synergistic effects with present medication should be considered.
A note on storing fresh juice: don’t. It’s best to drink it straight away. If you absolutely must store it, find a dark glass container (to exclude light) and fill it to the limit (to exclude oxygen) before capping and storing it in the fridge. For maximum benefit, drink as soon as possible, preferably on the same day. Tamme et al. (2010) showed that the nitrate/ nitrite content of homemade and small-scale industrially produced vegetable juices decreases/ increases markedly over 48h when not cooled. They also measured pH and noted a decrease of up to >2 units (that’s >100x more acidic than the fresh juice) within 48h of storage at c. 20°C. Keeping the juice cool helped preserve initial characteristics and slowed changes, including microbial growth (coliforms, moulds, yeast). Their data suggest one would probably be best off to drink freshly made juice right away, and to refrigerate lightly pasteurized commercial juice for no longer than 24h.
My preferred form of beetroot intake is juice. That said, beetroot in salad or soup works well too, and both are delicious options, as is roasted beetroot. Both cooked spinach and beetroot retain next to 100% of their nitrate content, so its bioavailability remains high after cooking (Lidder & Webb 2012), even though other beneficiary constituents (antioxidants) may decline with heat exposure.
It should be noted that we don’t yet have any long-term beetroot/ dietray nitrate supplementation studies (as in monitored effects of regular consumption for, say, one year or longer) to clearly establish its prolonged benefit at seemingly no risk. One study pointed out beetroot’s high oxalic acid content (Wruss et al. 2015), a substance that may cause gall and kidney stone formation. However, I believe, rather than looking at single ingredients, the whole aspect of a food is more important. We know little about the synergies that define how any given food affects an organism. I would not be surprised to learn that other (beetroot or dietary) constituents render oxalic acid harmless, for example (as is the case for vitamin C and other antioxidants which effectively inhibit carcinogen forming nitrosation reactions (Bryan & Ivy 2015)). Either way, consuming up to 500 mg oxalic acid a day is considered safe, so anyone drinking less than 1l of beetroot juice per day should be fine in this regard (Wruss et al. 2015). Additionally, Carpentier et al. (2014) found no negative impact on kidney physiology from one week of nitrate supplementation.
As with anything, a healthy balance is probably best. Incorporating beetroot frequently seems a good idea to me, and I do. Play with the intervals you like best. On the whole, it looks as though the benefits of dietary nitrate far outweigh potential risks (Wruss et al. 2015, Bryan & Ivy 2015, Milkoswki et al. 2009).
Other Observed Benefits from Beetroot
High Antioxidant Content
Its deep red color hints at ample presence of pigments. Beetroot’s antioxidant capacity partly stems from its rich betanin pigment content (300-600 mg/kg). Betanin defuses highly reactive radicals (Box 5), thus preventing oxidative damage to cell membranes (lipid peroxidation) and red blood cells (Clifford et al 2015). Betalain pigments reduce the risk of atherosclerotic plaque formation by protecting both LDL (low-density lipoprotein) and endothelial cells from oxidative stress caused byinflammation (Ninfali & Angelino 2013).
A study examining the antioxidant capacity of 23 juice drinks found beetroot the most effective, exceeding results of tomato, carrot, mixed vegetable, orange and pineapple juices. Only pomegranate showed a higher antioxidant capacity in the FRAP (free radical antioxidant power) assay (Clifford et al 2015). Interestingly, both antioxidant capacity and polyphenol content of a 70 ml beetroot juice shot markedly increased after simulated (experimental) digestion (Wottoon-Beard & Ryan 2011), indicating high bioaccessibility after consumption. Other vegetable juices tested showed similar trends, only at much lower values.
Liver Protective Effect
Research on rats showed prolonged beetroot juice consumption (28 days) exerted a protective effect on the liver when experimentally exposed to a carcinogen. Beetroot juice reduced biomarkers of liver injury and DNA damage, indicating an attenuating, liver protective effect (Clifford et al. 2015, Krajka-Kuzniak et al. 2012).
Anti-bacterial Effect & Wound Healing
Nitrite exerts an antibacterial effect and accelerates wound healing, with known effectiveness on infected skin blemishes. Salivary nitrite confers the same effect and at least partly explains why most animals instinctively lick a wound (Butler & Feelisch 2008).
Potential to Attenuate Adverse effects of Cancer Drugs, Use as Chemopreventive Agent and Cancer Treatment
Beetroot may lessen adverse effects of common cancer treatments and act as chemopreventive agent for breast cancer by promoting cancer cell death. It also exerted a protective effect on (rat) heart cells when combined with doxorubicin, a widely used cancer drug (but limited in its clinical application through causing irreversible heart toxicity) (Das et al. 2013).
Experiments with human breast and prostate cancer cell lines and healthy skin cells showed that beetroot extract affected both cancer cells and healthy cells. Both doxorubicin and beetroot extract exerted dose-dependent cell toxicity. Contrary to the cancer drug which inhibited all cell lines 100% at both highest test concentrations within three days, beetroot extract, while significantly less cytotoxic than doxorubicin, continued to decrease cancer cell growth rates over seven days. It also rendered healthy cells viable at >90% and >60% at highest concentrations. Thus, “red beetroot extract may have the potential to lower the serious adverse effects associated with doxorubicin (adriamycin) therapy. This may be especially relevant since high doses of this anticancer antibiotic are usually prescribed. Thus, studies are needed to evaluate whether the beetroot extract when used in combination with doxorubicin can mitigate its toxic effects” (Kapadia et al. 2012). The same paper reported of positive beetroot extract effects on human colon cancer cell lines, increasing apoptosis (cell death) and reducing cancer cell division without exhibiting cytotoxicity.
Other research consistently showed reduced incidence of experimental tumors on skin, lung, liver, and esophagus in various animal models when exposed to red beetroot extract (Betanin, the E162 food coloring agent) and its chemopreventive value in rodents (Kapadia et al. 2012, Kujawska et al. 2009). Chemopreventive agents act to reduce cell proliferation, angiogenesis (blood vessel development to the tumor), and inflammation. They also stimulate cancer cell death (Das et al. 2013). Beetroot’s betanin pigment is known to induce apoptosis, possibly one reason why beetroot has been used for a long time to treat intestinal and genital tumors. Juices of fresh roots or leaves were considered effective in tumor therapies of the digestive system, lung, liver, breast, prostate and uterus. The stability of betalains in beetroot juice has been considered crucial for its antitumor effect (Ninfali & Angelino 2013). High cellular activity of NO synthases (enzymes that generate NO) appear associated with cytostatic or cytotoxic effects on tumor cells. In vitro studies with human cancer cells point to an inhibitory effect of nitrite on cancer cell replication mediated by NO (Habermeyer et al. 2015).
Together, these results look promising and future studies should verify their clinical relevance. And in the meantime, nothing keeps us from enjoying beetroot.
Inflammation influences nitrate/ nitrite metabolism. Infections induced by bacteria, parasites, or viruses and inflammatory diseases such as gastritis, hepatitis, and colitis represent recognized risk factors for human cancers of the stomach, liver, and colorectum. Such inflammatory conditions enhance biosynthesis of NO, nitrite, and nitrate (Habermeyer et al. 2015). Thus, eating nitrate rich foods may support the body’s healing response by increasing NO availability. Experiments showed that beetroot supplements could possibly rival synthetic drugs in their anti-inflammatory effects. Beetroot (betalain) extracts reduced pain and inflammation in osteoarthritic patients and results from animal studies report similar findings (Clifford et al. 2015).
Improved Intestinal Health
Björne et al. 2004 examined the effect of salivary nitrite on gastric mucosal blood flow and mucus thickness.They concluded that dietary nitrate may protect intestinal health and confirmed the importance of oral microflora as symbiotic species that thrive on ingested food (nitrate) and in return provide their host with nitrite, the substrate necessary to generate NO in the stomach and circulation. In the acidic stomach, nitrite-containing saliva generates NO with a concomitant increase in mucosal blood flow. The firmly adherent mucus layer also increases in thickness, thereby protecting the gastrointestinal tract from chemical assault generated by pathogens, drugs, or digestion (Björne et al. 2004, Gilchrist et al. 2010).
Improved Cerebral Blood Flow
An MRI (Magnetic Resonance Imaging) study on people ?70 years of age showed that dietary nitrate increased plasma nitrite levels and cerebral blood flow within white matter. It suggests a possible use for improving regional brain perfusion in older adults in brain areas critical to executive functioning (e.g. memory) (Presley et al. 2011). Conditions to benefit could include age-associated dementia and cognitive decline, as they may exhibit restricted cerebral blood flow and hypoxia, both scenarios in which dietary nitrate showed promising results (Bond et al. 2013, Presley et al. 2011). A Near-Infrared Spectroscopy (NIRS) study in 40 healthy adults revealed that a single dose of nitrate (~ 5 mmol) from beetroot juice can modulate cerebral blood flow in response to task performance and potentially improve cognitive performance, suggesting one mechanism by which brain function may benefit from vegetable consumption (Wightman et al. 2015).
From a clinical perspective, “nitrate and nitrite has been shown to be beneficial in models of I/R injury [ischemic reperfusion – when blood flows back into tissues previously deprived of regular blood flow/ oxygen supply] to the heart, brain, liver, kidney, and lungs” (Weitzberg et al. 2010), with a maximum protective effect at a dose of 48 nmol of nitrite (liver and heart). Interestingly, a similar systemic load of nitrite can be achieved in humans by eating only 100 g of a nitrate-rich vegetable, such as beetroot or spinach (Weitzberg et al. 2010).
Potential to Attenuate Metabolic Syndrome
The term “metabolic syndrome” includes a cluster of risk factors for cardiovascular disease and type 2 diabetes mellitus, among them obesity, dyslipidaemia, hypertension, and insulin resistance. The prevalence of the metabolic syndrome reaches epidemic proportions. WHO estimates that 347 million people worldwide suffer from diabetes mellitus (McNally et al. 2015).
Experiments on rodents showed that seven weeks of dietary nitrate (NaNO3) treatment decreased weight gain, visceral fat, and plasma triglyceride concentrations compared to controls. It also improved glucose tolerance and reduced blood glucose concentrations (Carlström et al. 2010). These outcomes were achieved with a nitrate concentration corresponding to a daily dietary intake of 100 – 300 g of nitrate-rich vegetables (e.g. beetroot, lettuce, spinach) in humans.
Nitrate can readjust the energy imbalance in obesity and appears to target multiple aspects of the metabolic syndrome. “It is evident that the use of dietary inorganic nitrate as a tool to tackle the metabolic syndrome has great potential” (McNally et al. 2015).
Improved Sports Performance
Numerous studies demonstrated that 3–6 days of dietary nitrate supplementation reduces the oxygen cost (the rate of oxygen use for a task) of moderate intensity exercise and may enhance exercise tolerance in healthy, young adults (Wylie et al. 2013).
Sodium nitrate (NaNO3) reduced oxygen cost during standardized exercise within three days of dietary supplementation, apparently improving metabolic efficieny. Subsequent studies with beetroot juice as the nitrate source confirmed these results, reducing oxygen cost during maximal performance and significantly extending time-to-exhaustion (Weitzberg et al. 2010), an improvement equating approximately 1%–2% in sporting performance (Lansley et al. 2011). While the molecular mechanism behind these effects remains unclear, data point to central mitochondrial involvement (mitochondria = energy generating cell organelles) (Weitzberg et al. 2010) and the nitrate – nitrite – NO pathway (Lansley et al. 2011).
Other physical performance positively affected by nitrate supplementation (and resulting lowered oxygen cost) include cycling, rowing, knee extensor exercise, and treadmill walking and running. Time trials with competitive cyclists ingesting 0.5 l organic beetroot juice pre-race improved by 2.8% (4 km) and 2.7% (16.1 km), indicating not only a statistically significant result, but also a practically meaningful outcome for athletes (Lansley et al. 2011). Wylie et al. (2013) found the most effective beetroot dose for exercise tolerance in athletes was 140 ml of juice, approximately equating a nitrate concentration of 8.4 mmol.
Beetroot exerts a plethora of beneficial health effects, attributed to its high nitrate and antioxidant content. Human studies to date show beetroot reduces inflammation, averts oxidative stress, preserves endothelial function (protects blood vessels), restores brain blood flow, enhances athletic performance, and lowers blood pressure.
Each 2 mm Hg rise in systolic blood pressure increases the risk of mortality from ischaemic* heart disease by 7% and that from stroke by 10% (Siervo et al. 2015). Conversely, lowering blood pressure by 5 mm Hg reduces the risk of stroke by 35% and the risk of ischaemic heart disease by 21% (Bryan & Ivy 2015). Thus, even a small change in blood pressure may confer a most meaningful benefit. Beetroot juice reduces blood pressure profoundly and consistently (Wylie et al. 2013), by up to 10 mm Hg, and commonly 5 mm Hg. This is well worth anyone’s consideration, especially because it is known that a reduction of 5 mm Hg is associated with decreased cardiovascular morbidity and mortality, thereby sufficiently reducing the long-term risk of developing cardiovascular disease (Habermeyer et al. 2015). * [ischaemia: inadequate blood flow to a region, organ or tissue]
Therefore, a small increase in the habitual consumption of nitrate and polyphenol-rich beverages such as beetroot juice may not only benefit the individual, but also have a significant positive effect on public health at large (Wootton-Beard & Ryan 2011), protecting people’s cardiovascular system, strengthening their antioxidant defences, and helping to prevent oxidative stress damage (Clifford et al. 2015) with its potential knock-on effects. So….beet it!