The flesh and juice of grapefruit offer many benefits if you have high blood pressure. However, grapefruit also has many food-drug interactions of which you need to be wary as some of these involve some antihypertensive drugs and statins. I’ve provided an overview of the pros and cons of eating grapefruit and drinking its juice, below, but if you are on any medication do check the Patient Information Leaflet inside your packs to see if any grapefruit interactions are listed.
Why Grapefruit Is Good for Blood Pressure
As a member of the citrus family, grapefruit is a good source of vitamin C, with a single fruit supplying at least half your daily requirement. Grapefruit contain citrus bioflavonoids (eg limonene, hesperidin, tangeritin and naringenin) which also have powerful antioxidant and anti-inflammatory actions. Together, these antioxidants help to protect against hardening and furring up of the arteries – a key contributor to the age-related increase in blood pressure that occurs in many people.Why Grapefruit Is Good for Cholesterol
Grapefruit has more pith and membranes than most citrus fruit. These are rich in pectin, a soluble fibre that reduces cholesterol absorption. The high level of bitter naringenin present also has cholesterol-lowering properties.
Drinking grapefruit juice can lower your circulating LDL-cholesterol as much as taking a plant sterol supplement or using sterol-fortified spreads. Red grapefruit juice has the most powerful effect, and can lower ‘bad’ LDL-cholesterol by as much as 15% compared with around 7% for juice from blond grapefruit.Grapefruit Drug Interactions
Grapefruit juice interacts with the absorption and metabolism of numerous drugs. The end result is a massive increase in the blood levels achieved when taking a standard dose of these drugs. The interaction was discovered by accident when researchers were looking at how drinking alcohol affected the absorption of a particular blood pressure medication called felodipine (a calcium channel blocker). Grapefruit juice was used as a mixer to disguise the alcohol taste and, while the alcohol itself did not have a significant effect, the grapefruit juice greatly increased absorption and the resulting level of the drug within the circulation.How Exactly Does Grapefruit Affect Medicines?
Researchers have found that grapefruit alters the way drugs are handled in the body in several different ways. Some grapefruit components (eg naringen, furanocoumarins) block the production of an enzyme (CYP3A4) within the intestinal wall. This enzyme usually inactivates some drugs before they are absorbed, so switching off its release allows a greater amount of the affected drugs to pass into the circulation. This enzyme blockade is irreversible and lasts for at least 24 hours, so that drinking commercial grapefruit juice regularly, or eating fresh fruit segments, can cause certain drug levels to rise enough to cause overdose symptoms. Grapefruit also appears to affect the way the transport of certain drugs across the intestinal wall, and how they are broken down in the liver.Which Drugs Does Grapefruit Interact With?
The list of drugs with which grapefruit is known to interact is lengthening all the time, and includes some antihypertensive drugs (mainly calcium channel blockers such as felodipine, nicardipine, nifedipine, verapamil), some beta-blockers (eg carvedilol, used to treat congestive heart failure), some antidiabetic drugs (eg repaglinide), anti-arrhythmic drugs (eg amiodarone, quinidine, disopyramide), antihistamines, antiviral drugs, immunosuppressants, hypnotics, drugs used to treat erectile dysfunction (eg sildenafil, tadalafil, vardenafil), some migraine drugs and statin drugs used to treat a raised cholesterol level.
Are You Taking a Statin?
Statins are widely prescribed for people with high blood pressure as these may reduce the long-term risk of a heart attack of stroke – independent of your cholesterol levels.How Long Does the Grapefruit Effect Last?
Researchers investigated the duration of the interaction by asking ten, healthy volunteers to take 40 mg simvastatin with water, or with high dose grapefruit juice (200ml, three times a day for three days) and then one, three and seven days after they'd drunk the high-dose grapefruit juice.
The results showed that taking simvastatin with high-dose grapefruit juice increased its absorption and blood concentration by over 12-fold compared with water.