Daily ingestion of 397 mg of dietary nitrate reduces systolic blood pressure by approximately 8 mmHg in individuals with hypertension.

Study: Dietary nitrate provides sustained blood pressure lowering in hypertensive patients: a randomized, phase 2, double-blind, placebo-controlled study.

Drinking a glass of beetroot juice every day for a month lowered blood pressure in people with high blood pressure by about 8 points, just like the claim says.

Study: Inter-individual differences in the blood pressure lowering effects of dietary nitrate: a randomised double-blind placebo-controlled replicate crossover trial

This study found that drinking beetroot juice, which is high in nitrate, lowered blood pressure by about 7 points in healthy people — very close to the 8-point drop claimed for people with high blood pressure. So it supports the idea that nitrate can help lower blood pressure.

Study: Inorganic Nitrate Supplementation Lowers Blood Pressure in Humans: Role for Nitrite-Derived NO

This study found that taking nitrate from beet juice or pills lowers blood pressure by helping blood vessels relax. Even though it wasn't tested exactly on people with high blood pressure, the same process likely works in them too.

Study: Reduction in blood pressure following acute dietary nitrate ingestion is correlated with increased red blood cell S-nitrosothiol concentrations.

This study found that eating nitrate-rich foods like beetroot juice can lower blood pressure in the short term, which supports the idea that taking nitrate daily might do the same. It shows how nitrate works in the body to relax blood vessels.