Effects of increased nitrate intake from beetroot juice on blood markers of oxidative stress and inflammation in older adults with hypertension

Abstract

Background

Vascular oxidative stress and low-grade inflammation are important in the pathology of cardiovascular disorders, including hypertension. Cell culture and animal studies suggest that inorganic dietary nitrate may attenuate oxidative stress and inflammation through nitric oxide (NO), and there is a need to investigate whether this translates to humans.

Aim

In this randomised, placebo-controlled crossover study, by measuring a combination of multiple blood biomarkers, we evaluated whether previously reported benefits of dietary nitrate translate to a reduced oxidative stress and an improved inflammation status in 15 men and women (age range: 56–71 years) with treated hypertension.

Methods

We investigated the effects of a single ∼400 mg-dose of nitrate at 3 h post-ingestion (3H POST) and the daily consumption of 2 × ∼400 mg of nitrate over 4 weeks (4WK POST), through nitrate-rich versus nitrate-depleted (placebo) beetroot juice. Measurements included plasma nitrate and nitrite (NOx), oxidised low-density lipoprotein (oxLDL), F₂-isoprostanes, protein carbonyls, oxidised (GSSG) and reduced glutathione (GSH); and serum high-sensitive C-reactive protein (hsCRP), chemokines, cytokines, and adhesion molecules. Flow cytometry was used to assess the relative proportion of blood monocyte subsets.

Results

At 4WK POST nitrate intervention, the oxLDL/NOx ratio decreased (mainly due to increases in plasma nitrate and nitrite) and the GSH/GSSG ratio (a sensitive biomarker for alterations in the redox status) increased, compared with placebo (for both ratios P < 0.01). The relative proportion of classical (CD14⁺CD16⁻) monocytes decreased at 4WK POST for placebo compared to nitrate intervention (P < 0.05). Other oxidative stress and inflammatory markers were not altered by increased nitrate intake relative to placebo.

Conclusions

The data from this study point toward a subtle alteration in the redox balance toward a less pro-oxidative profile by a regular intake of inorganic nitrate from plant foods.

Clinical trial registry number

NCT04584372 (ClinicialTrials.gov).