Blood pressure: start with how many mmHg the effect actually is

Nitrate from beetroot is the firmest finding, with hibiscus and flaxseed behind it. But nearly every food effect lands between 1 and 4 mmHg.

This page is not for diagnosis or treatment. Food does not replace medication. If you are under treatment, talk to your doctor before changing your diet substantially.

What it is

Blood pressure is the force the blood exerts against the artery wall. The upper number is the pressure as the heart contracts, the lower as it refills. It shifts through the day and with posture and whatever you were doing a minute before, so an average of several readings means more than any single one. Sustained high pressure loads the arteries, the heart and the kidneys over time.

Where the evidence stands

The evidence here is wide but shallow. Twenty ingredients have human results, and almost every effect size is a single-digit number of mmHg.

Nitrate from beetroot is the firmest. The body converts it through nitrite into nitric oxide, which relaxes the vessel wall. The mechanism is clear and the results are consistent. Spinach works through the same pathway.

Hibiscus showed a dose-response. Seeing the effect scale with the dose is a signal that it is not an incidental association, and it is a rare luxury in food research.

Flaxseed is at the larger end for a food. It has to be ground, though, and the trials used more than most people eat.

And then the numbers are small. Grapes moved systolic pressure by 1.48 mmHg; black tea by 1.04. Statistically significant and visible on a home monitor are not the same claim.

Some results went the other way. Aronia's blood pressure findings were not what was expected, and kefir moved neither blood pressure nor CRP at all. The celery result came from 1.34 g of seed extract rather than the vegetable, and the −8 mmHg for soy milk sits in a paper whose own conclusion was that the difference was negligible. Two meta-analyses of spirulina in the same year reported −0.42 and −3.09.

What the evidence shows

These are the benefit entries from the ingredient articles, unchanged. Strongest grade first, and results that found nothing, or went the other way, are included.

Strong evidenceBeetroot
It lowers blood pressure[1]
Moderate evidenceHibiscus tea
Blood pressure fell dose-dependently[2]
Moderate evidenceFlaxseed
It lowers blood pressure — a large effect for a food[3]
Moderate evidenceGarlic
It lowers blood pressure, modestly[4]
Moderate evidenceCocoa
Blood pressure fell — in people who already had high blood pressure[5]
Moderate evidencePomegranate
The blood pressure evidence is relatively solid[6]
Moderate evidenceSpinach
Nitrates improve blood pressure and exercise efficiency[7][8]
Moderate evidenceOnion
Quercetin modestly lowers blood pressure[9]
Moderate evidencePumpkin seeds
Magnesium and blood pressure — but only when it is already high[10]
Moderate evidenceCashew
Lipids unchanged, systolic pressure down 3.39 mmHg — from 392 people[11]
Moderate evidenceWatermelon
Blood pressure fell — but not on watermelon's own account[12]
Moderate evidenceGrapes
It lowered systolic blood pressure by 1.48 mmHg[13]
Moderate evidenceBlack tea
Systolic blood pressure −1.04 mmHg — significant but small[14]
Moderate evidenceGreen tea
It nudges LDL cholesterol and blood pressure down[15][16]
Moderate evidenceKefir
Blood pressure and CRP did not change[17]
Early researchCelery
Blood pressure fell — but on 1.34 g of seed extract, not the vegetable[18][19]
Early researchSoy milk
8 mmHg lower on soy instead of cow milk — while the paper's verdict is "few differences"[20]
Early researchSpirulina
Two meta-analyses, one year: diastolic pressure −0.42 versus −3.09[21][22]
Not establishedAronia (chokeberry)
The blood pressure result went the other way[23]
Not establishedAmaranth
Claims about blood pressure, cholesterol and weight are unverified

What food can and cannot do

Larger levers exist before food.

A single food moves blood pressure by 1 to 4 mmHg. Cutting sodium, losing weight and walking regularly are each reported at larger magnitudes than that. Those come before this list.

If you take medication, do not cut it on your own. Blood pressure rebounds sharply when treatment stops.
Beetroot and other high-nitrate vegetables push in the same direction as the drugs. If you feel lightheaded, talk to your doctor.
Teas containing liquorice root can push pressure the other way. Check the ingredients when you change herbal teas.
Grapefruit interferes with the metabolism of some blood-pressure drugs. Read the leaflet if you take them.
Do not judge by one high reading. Several home measurements at a consistent time tell you more.

This page is not for diagnosis or treatment.

Related nutrients

Sources

The databases and health authorities this article's nutrition figures and health statements draw on.