The dose-response effects of nitrate-rich beetroot ingestion on cardiovascular and endothelial function: a randomised controlled trial.

Dietary nitrate supplementation increased plasma nitrate and nitrite concentrations across all doses.

• Three doses were tested: 200 mg, 400 mg, and 800 mg NO3--rich beetroot powder.
• Measurements were taken prior to (control) and 2.5 hours post supplement ingestion.
• The study used a double-blind, randomised, crossover design.
• Plasma [NO3-] and plasma [nitrite] were both elevated following supplementation, but no between-dose differences in effect on cardiovascular outcomes were reported for arterial stiffness.

Arterial stiffness markers improved following all three nitrate doses, with no significant differences between doses.

• All three doses (200 mg, 400 mg, and 800 mg NO3-) resulted in improvements in arterial stiffness markers.
• No between-dose differences were observed for arterial stiffness outcomes.
• Measurements were taken 2.5 hours post ingestion.
• This suggests a threshold effect may exist at the lowest dose tested (200 mg) for arterial stiffness.

Macrovascular endothelial function only improved following the 400 mg nitrate dose.

• Endothelial function improved by +3.07% compared to control following the 400 mg dose.
• The 200 mg and 800 mg doses did not produce significant improvements in endothelial function.
• This non-linear dose-response suggests an optimal intermediate dose for endothelial function.

Aortic systolic blood pressure only improved following the highest nitrate dose of 800 mg.

• Aortic systolic BP was reduced by -4 mmHg compared to control following the 800 mg dose.
• The 200 mg and 400 mg doses did not produce significant reductions in aortic systolic BP.
• This indicates a higher dose threshold is required for aortic systolic BP reduction compared to other cardiovascular outcomes.

Dietary nitrate supplementation had no effect on brachial artery blood pressure.

• None of the three doses (200 mg, 400 mg, 800 mg) significantly altered brachial BP compared to control.
• This was measured at the 2.5-hour post-ingestion time point.
• The absence of a brachial BP effect contrasts with improvements seen in aortic systolic BP at the highest dose.

Dietary nitrate supplementation had no effect on plasma cyclic guanosine monophosphate (cGMP) concentration.

• cGMP is a downstream signalling molecule in the nitric oxide pathway.
• None of the three doses altered plasma [cGMP] compared to control.
• This finding suggests the cardiovascular improvements observed may not be fully explained by the canonical NO-cGMP signalling pathway, or that venous plasma cGMP is not a sensitive marker of this response.