Fruits and vegetables are loaded with beneficial vitamins, minerals, flavonoids and phytochemicals. Citrus, including grapefruit, provides vitamin C and fiber, important for health. Even the DASH diet, a diet found to improve blood pressure, encourages the consumption of grapefruit. However, blood pressure medications may carry warning labels for this otherwise healthful fruit.
Effects
Grapefruit juice decreases the expression of the enzyme cytochrome P450 3A4 in the small intestine wall. This enzyme normally interferes with the availability of certain medications, including those taken for high blood pressure. By decreasing this enzyme, grapefruit juice allows more of the drug to be absorbed in the blood and increases its effect. This increased availability can lead to a dangerous drop in blood pressure.
Duration
Food and drug interactions may be avoided by ingesting them separately, as noted on medication warning labels. This does not hold true for grapefruit or its juice and blood pressure medication. The grapefruit juice effect duration may be up to 24 hours. There is no safe time to consume grapefruit juice when taking blood pressure medication.
Availability
A study published in 1997 from the University of Michigan found that one glass of grapefruit juice increased availability of blood pressure medications by 267 to 345 percent. There is also a cumulative effect--the more often the grapefruit juice is consumed, the greater the affect on blood pressure. This same study found that drinking grapefruit juice three times a day for five days increased medication availability up to 538 percent.
Individual Variability
The amounts of intestinal enzymes differ from person to person; therefore, the impact on blood pressure medication will differ as well. If your medication carries a warning to avoid grapefruit juice, you should follow it.
Not All Citrus is the Same
Not all citrus fruits have the same affect as grapefruit. Pay attention to the warning label on your medication. If it says to avoid "grapefruit" or "grapefruit juice," this does not mean all citrus fruit. You may still enjoy the benefits of oranges, tangerines and even lemons. Consult your physician or pharmacist if you have any questions or concerns.
References
- "Nutrition Journal"; Medicinal importance of grapefruit juice and its interaction with various drugs; Jawad Kiani, Sardar Z Imam; October 2007
- "The Journal of Clinical Investigation"; Grapefruit juice increases felodipine oral availability in humans by decreasing intestinal CYP3A protein expression; KS Lown, DG Bailey, RJ Fontana, SK Janardan, CH Adair, LA Fortlage, MB Brown, W Guo, PB Watkins; May 1997
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