High Blood Pressure? Eat More Grapefruit

A Canadian pharmacologist discovered grapefruit’s effects on medications by accident—and his findings have saved many lives.

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Citrus paradisi, commonly known as grapefruit, and so named because of its grape-like clusters in the tree it grows in, belongs to the Rutaceae family and comes in white, pink, and red varieties. Each type offers a burst of flavor ranging from intensely tart to deliciously sweet, so whatever your preference, you are sure to find a variety that suits your tastes.

A hybrid of sweet oranges and pomelos, grapefruit are thought to have originated in the islands of the West Indies around the 1700s. They were exported a century later, arriving in Florida in the early 1800s, where they have been cultivated ever since. Grapefruit is now grown predominantly in Florida, Texas, California, and Arizona, but the world’s largest producer is China, producing more than 50 percent of the world’s grapefruit supply.

Loaded with vitamins A and C, grapefruit is a good source of dietary fiber and has an extremely low glycemic index of 25. The glycemic index measures how much a food raises blood glucose levels—making grapefruit an excellent option for those with diabetes.

Grapefruit also contains vitamin B6, magnesium, calcium, thiamine, and folate. Perhaps most importantly, grapefruit contains potassium, vital for controlling heart rate and blood pressure, as well as maintaining normal fluid levels inside our cells—which is balanced by sodium, which keeps normal fluid levels outside our cells. One grapefruit supplies about 10 percent of our daily potassium requirements, according to Johns Hopkins Medicine.

In addition to lowering blood pressure, studies have shown that grapefruit can help with weight loss, reduce cellulite, beautify skin, boost the immune system, reduce the risk of strokes, and even protect against cancer.

Grapefruit for Lowering Blood Pressure

High blood pressure, or hypertension, is a serious condition and a risk factor for heart disease and stroke.

Nearly half of Americans over 20 have high blood pressure—representing a staggering 122 million people, according to a 2023 report from the American Heart Association. The likelihood of having high blood pressure increases as we age, reflected in the fact that three-quarters of Americans over 65 have the condition.

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Grapefruit is effective for lowering blood pressure because of its high potassium content, which counteracts the adverse effects of sodium—a common cause of high blood pressure. However, those already on blood pressure medications must exercise caution when consuming grapefruit—but more on that in a moment.

Multiple studies support the use of grapefruit for lowering blood pressure.

A randomized controlled trial published in Metabolism took 74 overweight adults and split them into two groups. One was given half a grapefruit before each meal (three times a day), and the control group didn’t eat any grapefruit. In addition to the results of lowering blood pressure, the grapefruit group lost weight, decreased their waist circumference, and had a decrease in LDL cholesterol (low-density lipoprotein).

In another study published in the British Journal of Clinical Pharmacology, grapefruit juice enhanced the systolic blood pressure-lowering effects of beetroot juice.

A systematic review and meta-analysis set out to evaluate evidence for or against the effect of grapefruit consumption on body weight, blood pressure, and lipid profiles. The researchers’ analysis found a significant decrease in systolic blood pressure compared to controls.

Grapefruit is high in potassium, and studies show that greater potassium consumption can lower blood pressure. A systematic review of 22 randomized controlled trials found that increased potassium intake reduced both systolic and diastolic blood pressure in adults with hypertension. Interestingly, the study also found a decreased risk of stroke with increased potassium intake.

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Grapefruit Interactions with Medications

A 1991 clinical trial published in The Lancet showed that grapefruit drastically increased the absorption of some medications—meaning regular doses could be turned into potentially deadly overdoses. The trial studied the effects of felodipine and nifedipine, medications used to treat high blood pressure. Six men with borderline hypertension (high blood pressure) took 5 milligrams of the drug felodipine with either water, grapefruit, or orange juice. When taken with grapefruit juice, the bioavailability of felodipine averaged 284 percent (but ranged between 164 to 469 percent) compared to when taken with water. When the same test was repeated with 10 milligrams of nifedipine, its bioavailability with grapefruit juice was 134 percent (with a range of 108 to 169 percent) compared to that with water.

Canadian pharmacologist David Bailey, who received his doctorate in pharmacology from the University of Toronto, initially made the discovery.

According to an article in The Globe and Mail, Mr. Bailey stumbled upon the discovery by accident while researching the effect of alcohol on the blood pressure medication felodipine in the late 1980s. He wanted to disguise the taste of the alcohol and did so using grapefruit juice. Bailey later noticed that the subjects taking the medications with grapefruit juice had higher levels of the drug in their bloodstream. With further exploration, he discovered that the grapefruit juice inhibited a specific enzyme called CYP3A4 that helps break down the medication in the gut. The result is that the body absorbs more of the drug.

Mr. Bailey’s discovery resulted in the Lancet article mentioned above, and the phenomenon came to be known as “the grapefruit effect.”

Mr. Bailey’s subsequent research revealed grapefruit’s interactions with approximately 100 oral medications, where its effects either increased levels of the drug in the body to potentially dangerous levels, or the opposite—reducing their effectiveness.

His pioneering work has led to many medications having warning labels, alerting patients not to take them with grapefruit juice.

Some examples of medications that can interact with grapefruit juice are:

• Statin drugs used to lower cholesterol.
• Medicines to treat high blood pressure.
• Organ-transplant rejection drugs.
• Anti-anxiety medications.
• Corticosteroids.
• Medications used to treat arrhythmias (abnormal heart rhythm).
• Antihistamines.

Although reactions vary from person to person, it’s important to carefully read the labels and inserts of any medications you are taking to see if grapefruit juice could interact with them. If you are not sure, ask your health care provider or pharmacist and take medications with water.

A helpful video by the U.S. Food and Drug Administration breaks down grapefruit’s potential effects on some medications.

Mr. Bailey passed away in August 2022 at the age of 77 and leaves behind an important legacy. His discovery has saved many lives and helped to further our understanding of grapefruit’s effects on a multitude of medications.

Final Thoughts

Despite its effects on some medications, grapefruits are nutrient-dense superfoods packed with vitamin C—needed to support a healthy immune system—plentiful antioxidants, fiber, and potassium. If you struggle with high blood pressure and want to try to reduce it naturally, adding grapefruit to your diet may be helpful. A great way to get more grapefruit into your diet and reap its health benefits is to add it to a salad, use it to make a tangy salsa, or slice one in half and eat the segments with a spoon in the classic breakfast style.

Remember, if you are taking medication for high blood pressure, or any other condition, be sure to speak to your physician or pharmacist to ensure that grapefruit won’t interact with your particular medication.

Ruby grapefruit salad with Asian lettuces and candied grapefruit zest at Tinker Street. (Courtesy of Tinker Street)