Beetroot juice (also called beet juice) may have a very modest effect on lowering blood pressure. Most beetroot supplements, however, are unlikely to provide this benefit.
The blood pressure effects seem to relate to the high concentration of nitrate in beetroot. Bacteria in the mouth convert this nitrate into nitrite, which is then either absorbed or changed into nitric oxide in the stomach. Nitrite and nitric oxide improve endothelial function (the ability of blood vessels to dilate and contract), which, in turn, can help lower blood pressure. Other nitrate-rich foods are green leafy vegetables and salad greens such as watercress, chervil, rocket (arugula), and spinach — and there's some preliminary evidence that these may also lower blood pressure (Jonvik, J Nutr, 2016).
Clinical studies with beetroot have generally shown only a modest and limited effect on blood pressure. Pooling the results from 16 randomized, controlled trials, researchers found that beetroot was associated overall with a reduction in systolic blood pressure of just 4 mm Hg, with no significant effect on diastolic blood pressure. In addition, the effect on systolic blood pressure was mainly observed at night and the effect tended to be smaller on older individuals. The studies used in the analysis included a total of 245 people and lasted from 2 hours to 15 days and used beetroot juice or inorganic nitrate (Siervo, J of Nutr 2013).
Interestingly, a study not included in the analysis noted above used a single dose of beetroot in 30 healthy adults, ages 23 to 68, who consumed either a single 500 gram (about 2 cups) dose of beetroot and apple juice or all-apple placebo juice, after which they had their blood pressure monitored for 24 hours. No overall effect was seen, although, the men (not women) did have a significant reduction in systolic blood pressure (close to 5 mm Hg) 6 hours after consuming the beetroot juice (Coles, Nutrition Journal 2012).
In a study in Tanzania among older adults (average age 60) with high blood pressure (average blood pressure 152/92 mm Hg), drinking 70 mL (about ¼ cup) of concentrated beetroot juice providing about 400 mg nitrate (Beet It shots, James White Ltd) daily for 60 days modestly decreased blood pressure. Average systolic pressured decreased 10 mm Hg (vs. 0.3 mm Hg with placebo) and diastolic pressure decreased 5.4 mm Hg (vs. an increase of 1.6 mm Hg with placebo). Although some evidence suggests that folic acid may play a role in endothelial function and/or reduce blood pressure in some people, those who took folic acid (5 mg/day) in addition to the beetroot juice had smaller and non-significant decreases in systolic and diastolic blood pressure compared to those who drank beetroot juice only (Siervo, J Nutrition 2020).
There's some evidence that beetroot juice may also have positive effects on blood pressure during subsequent exercise, including one study of 12 older people who consumed either nitrate-rich beetroot juice (70 mL twice a day) or nitrate-depleted beetroot juice (placebo) for three days before walking on a treadmill. Systolic and diastolic blood pressure readings in the nitrate-rich juice group were 5 points and 3 points lower than in the placebo group (Kelly, Am J Physiol Regul Integr Comp Physio 2013). Such a study suggests that the nitrates in beetroot juice were responsible for the blood pressure effect, rather than other compounds.
Other studies have used beetroot supplementation over slightly longer periods of time — also with mixed results. For example, in a 2-week study of 27 older people with type 2 diabetes, nitrate-rich beetroot juice (about 1 cup daily) had no effect on blood pressure, as measured by a 24-hour ambulatory blood pressure monitor (Gilchrist, Free Radic Biol Med 2013) ; neither did a nitrate-depleted beetroot juice, which served as the control. Likewise, a study of 27 people with treated hypertension found no blood pressure benefit from drinking either a nitrate-rich or nitrate-depleted beetroot juice for 7 days (Bondonno, AJCN 2015). But in a 4-week study of 68 people with hypertension, nitrate-rich beetroot juice (about 1 cup daily) reduced blood pressure (by 7.7 to 8.1 points systolic and 2.4 to 5.2 points diastolic), with no changes seen from a nitrate-depleted beetroot juice (Kapil, Hypertension 2015).
If you have hypertension (high blood pressure), beetroot is definitely not a substitute for blood pressure drugs, and you shouldn't stop your medication or change your dosage without talking to your doctor.
Individuals with a history of calcium oxalate kidney stones should be aware that beetroot juice can contain high amounts of oxalate (60 mg to 70 mg per 3.4 oz. serving) (Sierer, J Food Compost Anal).
Be aware that beetroot can turn urine and stools red.
What else is in beetroot?
Besides its nitrate, beetroot is a source of many nutrients including folate, potassium, B vitamins, magnesium, and zinc, along with fiber and other bioactive compounds, notably polyphenols and betalain pigments (beta-cyanins, which give beets their characteristic red/purple colors, and beta-xanthins, which provide the yellow color of yellow beets). Among their potential benefits, polyphenols and betalains have antioxidant properties that may help protect against oxidative damage, which is implicated in hypertension and other chronic conditions.
The bottom line:
Beetroot juice may provide a very modest reduction in blood pressure. This effect has mostly been demonstrated in young healthy individuals in short-term studies and the effect is largely limited to systolic blood pressure, not diastolic blood pressure. However, one study in people with high blood pressure found beetroot juice to modestly decrease both systolic and diastolic blood pressure. Effects on blood pressure have been seen when consuming about one cup of beetroot juice daily (which provides roughly 300 to 400 mg of nitrate). A higher dose (2 cups) may provide a somewhat greater effect. Although capsules of beetroot are sold, these tend to contain only a small amount of powdered, dried beetroot (about 500 mg per capsule), which would only provide only about 1% of the nitrate in a cup of beetroot juice. (It takes about 1 pound, or roughly 450,000 mg, of fresh beetroot -- which is about 90% water -- to produce a cup of beetroot juice). If you are counting calories, a cup of beetroot juice has about 110 calories.