EFFECTS OF DIETARY NITRATE FROM VEGETABLES ON BLOOD PRESSURE IN HEALTHY HUMANS

Abstract

Dietary nitrate is a naturally occurring component of vegetables and nitrate salts have been used for centuries as preservatives in processed meats. Up until recently, nitrate has been considered as a harmful contaminant. However, more recent research suggests that dietary nitrate supplements can reduce blood pressure (BP) and could be beneficial to cardiovascular health. This is important as 1 in 4 adults world-wide have hypertension, the largest single risk factor for cardiovascular disease. Three studies were conducted in order to assess the effects of dietary nitrate, obtained from vegetables, on BP in healthy humans.

The first study evaluated the effect of supplementing the diets of healthy young men with high-nitrate vegetables following a randomised crossover trial. They received vegetable boxes of either high-nitrate or low-nitrate vegetables over a two-week period. BP was measured and blood samples were obtained to analyse nitrate and nitrite concentrations prior to a moderate exercise test at the beginning and end of each two-week period.

The second study evaluated the same question but in a group of healthy young women. They were randomised in a crossover trial to receive boxes of high-nitrate vegetables, or to a control diet avoiding high-nitrate vegetables for one week. BP was measured and blood samples were obtained.

A third study was conducted to estimate dietary nitrate intake and its effect on BP and resting metabolic rate (RMR) in a group of healthy vegetarians, previously reported to have high nitrate intakes, compared to a similar group of omnivores. Following a single blind and non-randomised design, participants were provided with placebo mouthwash for seven days and then antibacterial mouthwash for a further seven days. BP and RMR were measured after both interventions. Dietary nitrate intake was estimated in both groups and blood and salivary samples were obtained.

This thesis concludes that consumption of high-nitrate vegetables lowered BP in healthy young women. However, this effect was attenuated in healthy young men. Additionally, there were no differences in nitrate intake, BP or RMR between vegetarians and omnivores. Further research is required before dietary nitrate can be considered as a nutrient beneficial to cardiovascular health.