The cardiovascular effects of watercress on human health and performance

Burke, Rachel Robertson

Abstract

The purpose of this thesis is to assess an alternative dietary nitrate supplement as a possible ergogenic aid and to evaluate its therapeutic potential upon cardiovascular markers in healthy young and old age populations. The first experimental chapter of this thesis (Chapter 4) aimed to investigate the efficacy of an alternative dietary nitrate supplement. Watercress juice was compared to beetroot juice, a well-established, commercially available, dietary nitrate supplement, to sodium nitrate and to water, acting as control. The sodium nitrate condition would enable further insights into the mechanism of nitrate rich supplements. The first study aimed to investigate the acute effects of nitrate supplements on cardiovascular and oxidative/nitrosylative stress parameters at rest and following a 16.1 km cycling time trial on a SRM cycle ergometer (16.1 km TT). Participants (n=9) were randomly assigned to consume nitrate matched supplements and water. Plasma nitrate concentration significantly increased at 120 mins post-ingestion for the dietary nitrate conditions, (P < 0.05). However, plasma nitrite concentrations did not significantly increase, (P > 0.05). Watercress supplementation demonstrated a 1.4% performance improvement compared to the water trial and the fastest time (1655.1 (110.2) secs). Compared with beetroot juice (1673.8 (96.0) secs), sodium nitrate (1685 (102.3) secs) and water (1677.9 (129.8) secs). Interestingly, sodium nitrate observed the slowest time. The difference between trials were not significantly different (P = 0.31). However, a critical improvement in performance has been reported small as 0.5 - 1.5 % (Paton & Hopkins, 2006). Using this criterion, it is possible that our findings may be of real-world relevance. Watercress supplementation was the only supplement to indicate an increase in forearm blood flow (+0.18 (0.03) %/min), from baseline to 120 mins post-ingestion but this was not significant (P = 0.73). Beetroot decreased but was equivocal (-0.88 (0.30) %/min) (P = 0.25). Sodium nitrate tended to decrease (-0.60 (0.04) %/min) (P = 0.07) and water significantly decreased (-0.61 (0.01) %/min) (P = 0.03). These results suggest that there is potentially a synergistic effect between the nitrate content and other bioactive components in watercress or there is an effective bioactive component that is not nitrate which may have enhanced cycling performance in a young healthy physically active population.

Assessing nitrate supplementation in a cardiovascular compromised population, rather than young, physically active volunteers may provide further mechanistic insights. Therefore, the aim of the second experimental Chapter 5 was to investigate the efficacy of watercress supplementation on cardiovascular and oxidative/nitrosylative stress markers in a normoxic and hypoxic setting in a healthy, physically active, aged population. Participants (n=9) were randomly assigned to consume watercress supplement and water (control) in normoxic and normobaric hypoxic environment. Oxygen saturation significantly decreased (P < 0.05) in hypoxic environments; the control condition at 30 mins (-6 (2.4) %) and 120 mins post-ingestion (-6 (3.2) %) and watercress at 30 mins (-4 (2.4) %) and 120 mins (-2 (2.3) %) post-ingestion. Plasma nitrate concentration significantly increased (P < 0.05) in the watercress normoxic condition at the 30 mins (+14.2 (6.7) μmol/L) and 120 mins post-ingestion (+13.8 (5.7) μmol/L); and in the watercress hypoxic condition at the 30 mins (+12.3 (5.9) μmol/L) and 120 mins post-ingestion (+8.4 (9.7) μmol/L). However, plasma nitrite concentration did not change (P > 0.05). There were no differences in vasodilatory or oxidative/nitrosylative stress measures. Acute watercress supplementation containing 400 mg of nitrate does not improve vascular function or attenuate oxidative stress biomarkers in a healthy aged population at rest under normoxia or hypoxia.

With the substantial variation seen in a range of measures in Chapters 4 and 5. The purpose of the third experiment, Chapter 6, was to assess the error of measurement to support the interpretation of the previous findings. Therefore, the aim of this work was to investigate the repeatability of forearm blood flow, 16.1 km cycling TT performance on a SRM cycle ergometer (one week apart) and the change in oxidative/nitrosylative stress markers at baseline and after the TT, in a healthy, physically active, male cohort in normoxic conditions. There was limited difference between 16.1 km TT performance times and the coefficient of variation was low 1% (90% CI; 0.7% -1.9%). Forearm blood flow observed a high coefficient of variation of 39.3% (90% CI; 31.6 – 99.5%). Baseline and post TT for both oxidative/nitrosylative stress markers reported a large variation. For example, baseline protein carbonyls concentration across the two visits showed a high coefficient of variation of 65.5% (90% CI; 43.6 - 136.7%). Therefore, the primary findings from this investigation suggest that a 16.1 km TT, on a SRM cycle ergometer in a physically active, male cohort, is highly repeatable The low CV suggests that this test can enable sports scientists and trainers to better comprehend factors (e.g. ergogenic aids) that may influence cycling performance. In contrast, the repeatability of forearm blood flow was high and oxidative/nitrosylative stress markers, one week apart, demonstrated a high variability. Therefore, using these markers in a repeated measures research design should be used with caution.

Citation

Burke, R. R. The cardiovascular effects of watercress on human health and performance. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4222526

• Thesis Type: Thesis
• Deposit Date: Jul 7, 2020
• Publicly Available Date: Feb 23, 2023
• Keywords: Sports science
• Public URL: https://hull-repository.worktribe.com/output/4222526
• Additional Information: Department of Sport, Health & Exercise Science, The University of Hull
• Award Date: Nov 1, 2019