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Nitrate Lab Report
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The Effect of Beetroot Juice on Blood Pressure and the Oxygen Cost of ExerciseIntroduction
Diets that are high in vegetables have been found to benefit health and also is associated with
a longer life span (Visiolo, Bogani, Grande & Galli, 2005). The consumption of vegetables is
known to decrease the risk of coronary heart disease (CHD), strokes and diabetes (Joshipura
et al. 2001). Dietary nitrate is found in green leafty vegetables and beetroot, where they
contain around 250 mg per 100 g of fresh weight (Lundberg et al. 2009). Beetroot,
particularly, is high in inorganic nitrate and the nitrate is removable to create the placebo
(Gilchrist, Shore & Benjamin, 2010).
Nitric oxide is produced in the body via two pathways; the nitric oxide synthase pathway and
the entero salivary pathway (Sobko, Marcus, Govoni & Kamiya, 2010; Lundberg, Weitzberg
& Gladwin, 2008). The first of these is the bodies natural way of creating nitric oxide (NO)
via the semi essential amino acid, L-arginine (Moncada & Higgs, 1993). Nitrogen enzymes
use L-arginine and molecular oxygen to create NO, the free radical gas (Lundberg et al.
2008). NO has a limited lifetime withing the body and is limited diffusion capacities
(Lundberg et al. 2008). It can however be stabilised in the blood and tissue via oxidisation,
from nitrate to nitrite; this is done by xanthine oxidase and an anaerobic bacterium (Lundberg
et al. 2008). This creates the ability for the nitrite to enter the blood and make its way to the
working muscles (Lundberg et al. 2008). The second pathway is via the consumption of
foods that contain dietary nitrate. The nitrate is swiftly absorbed in the upper gastrointestinal
track and the nitrate mixed with the previously formed NO (made from the nitric oxide
synthase enzyme), creating an oxidisation reaction in the blood (Lundberg et al. 2008). This
is then taken to the salivary glands (around 25%) and the rest is excreted via urine (Lundberg,
Weitzberg, Cole & Benjamin, 2004). This then enters the oral cavity where the facultative
anaerobic bacterium uses the nitrate as an alternative electron accepter instead of oxygen in
respiration, reducing the nitrate to nitrite by the process of nitrate reductase (Duncan et al.
1995). When the saliva then enters the acidic stomach, it converts nitrite to nitrous acid,
which later decomposed to produce NO and nitrogen oxides (Lundberg, Weitzberg &
Lundberg, 1994). This can be enhanced by Vitamin C which can also be found within the diet
(Weitzberg & Lundberg, 1998).
Vanhatalo et al. (2010) found that a 500 ml per day of beetroot juice resulted in a 3 %
decrease in systolic blood pressure (BP) and a 4 % decrease in diastolic BP. This may not
, seem like a large decrease; however, it may be vital in hypertensive patients preventing
around 75000 deaths year (Saunders, 2007). A 5 % reduction in BP can be seen to reduce the
risk of stroke by 22 % and CHD by 19 % (Vanhatalo et al. 2010). Kelly et al. (2013) found a
2.5 day supplementation showed a decrease in both systolic and diastolic BP. Wylie et al.
(2013) showed a dose of 8.4 mmols resulted in peak reductions of systolic BP. It was also
shown that an average decrease of 3.7 mmHg was found in diastolic BP (Larsen, Ekblom,
Sahlin, Weitzberg & Lundberg, 2006). Nitric oxide is a mediator of vasodilation (Vanhatalo
et al. 2010).
The oxygen cost of exercise was seen to reduce by 5 % after three days of supplementation in
low and high intensity exercise (Bailey et al. 2009). Larsen et al. (2011) found a reduction in
V̇O2 during submaximal work and an increase in muscular efficiency, through a quantity of
inorganic nitrate that can be consumed in a vegetable rich diet. The oxygen sparing effect of
nitrate happened without changes to the circulating nitrate concentrations, whilst work
performance was maintained or improve, which highlights a more efficient metabolism or
improved mechanical efficiency (Larsen et al. 2011). This implies the effect may be on the
mitochondria, meaning the ATP has become more efficient (Larsen et al. 2011). This may be
linked to the phosphate/oxygen ration (P/O ratio) which measures the amount of oxygen used
per ATP produced (Hinkle, 2005). Nitrate reduces factors that decrease P/O ratio efficiency
for example proton leakage and proton slippage (Brand, Chien, Ainscow, Rolfe & Porter,
1994; Groen, Berden & Van Dam, 1990).
Considering all the previous evidence, the hypothesis was set as the beetroot juice will reduce
BP and the oxygen cost of exercise.
Method
Participants
10 participants were consented (Mass 77.03 kg ± 10.11 kg and height 1.76 m ± 0.08 m).
Participants were asked to not use mouthwash during the consumption of the beetroot juice as
it reduced the nitrate-reducing bacteria within the mouth (Petersson et al. 2009).
Procedure
The participants visited the laboratory on one occasion where they completed a time to
exhaustion test (TTE). Before any exercising commenced the participants height (Seca 213,
Seca, UK) and body mass (Seca 770, Seca, UK) were taken. This allowed the body mass
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