1. Nitrate – a new nutrient?
Introduction
Nitrate is not recognized as a nutrient essential for health.
Recent studies at the University of Exeter and elsewhere have
demonstrated that dietary nitrate, via conversion to plasma
nitrate and nitrite, can reduce blood pressure. This has
exciting implications for future prevention of cardiovascular
diseases. Previous UK studies have used beetroot juice or
other nitrate supplements, rather than whole vegetables. We
tested the hypotheses that supplementation with high nitrate
vegetables, eaten as part of a normal diet will:
• increase plasma nitrate and nitrite and
• reduce blood pressure.
We hypothesised that low nitrate vegetables would not have
these effects.
Method
Having obtained ethical approval, 15 healthy, physically
active, male participants were recruited (average age 25 +/- 6
years). Participants were randomised in a 6-week, cross-over
design to receive high or low nitrate vegetables for 2 weeks,
with a 2-week ‘wash-out’ diet (normal diet with no restrictions)
in between. Participants changed the vegetable component of
their diets only and otherwise ate their normal diet. Before and
after each 2-week period, participants had their blood
pressure measured and had a blood test. Vegetables were
delivered to participants weekly by Riverford Organic Farms
Ltd. High nitrate vegetables included green leafy vegetables,
leeks, celery and fennel. Low nitrate vegetables included
tomatoes, onions, peppers, cucumber and carrots.
Quantitative dietary assessments were carried out to assess
nitrate intake. Data were analysed using two way repeated
measures ANOVA, post-hoc Fisher’s LSD tests and
significance accepted at p < 0.05. Correlations were assessed
using Pearson’s product-moment correlation coefficients.
Results
Supplementing the diets of physically active, young, males with
high nitrate vegetables:
 significantly increased estimated nitrate intake
 significantly increased plasma nitrate and nitrite (Figure 1)
 resulted in a significant correlation between diastolic blood
pressure and plasma nitrite (Figure 2). So, as plasma nitrite
increased, blood pressure dropped.
In contrast, low nitrate vegetables did not produce these effects.
Conclusions
Supplementing the diets of healthy, young, males with high
nitrate vegetables increased plasma nitrate and nitrite, which
correlated with a downward trend in blood pressure.
A small reduction in blood pressure in the UK population could
prevent nearly 40,000 deaths from stroke and heart disease
each year as well as prevent associated disabilities.
To increase consumption of high nitrate vegetables, current
public health advice to eat ‘5 A Day’ could be changed to ‘5 A
Day, plus leafy veg’, to improve health and prevent
cardiovascular disease.
Ann Ashworth, Stephen J. Bailey, Jamie R. Blackwell,
Fred Dimenna, Giles M. Hayward, Anni Vanhatalo, Andrew M. Jones
Sport and Health Sciences, St. Luke’s Campus, University of Exeter, Heavitree Road, Exeter, EX1 2LU.
High nitrate
vegetables:
Low nitrate
Vegetables:
Spinach Carrots
Lettuce Onions
Rocket Tomatoes
Figure 1: Effects of high and low nitrate vegetables on plasma nitrite in 15
participants.  Different from before high nitrate diet (p < 0.05)
Figure 2: Pearson’s product-moment correlation coefficient between the
change in diastolic blood pressure and the change in plasma nitrite
following two week’s supplementation with high nitrate vegetables.
0
50
100
150
200
250
300
350
400
450
before high
nitrate diet
after high
nitrate diet
before low
nitrate diet
after low
nitrate diet
Plasma
nitrite
(nM)
