Meanwhile a researcher at Kanazawa Medical University in Japan showed that nobiletin, a compound found in tangerines, has also demonstrated possible action against colon cancer.

Cancer of the colon or rectum is the second deadliest form of cancer after lung cancer but is also considered one of the most preventable types of cancer, as there are several dietary factors that appear to play a protective role against the disease.

In another trial, presented yesterday at the symposium on health benefits of citrus fruits, taking place during the American Chemical Society's national meeting this week, a team from the University of Hawaii reported that drinking grapefruit juice may help reduce the risk of cancer in smokers.

In a controlled study involving 49 smokers, the researchers found that those drinking three 6-ounce glasses of grapefruit juice a day reduced the activity of a liver enzyme called CYP1A2 that is thought to activate cancer-causing chemicals found in tobacco smoke.

The meeting underlines the nutraceutical potential of the fruit at a time when sales are being hit by the current trend for low-carb diets as well as warnings about the interaction between grapefruit and prescription drugs.

Grapefruit are a key component of the once fashionable ‘grapefruit diet', now pushed to the sidelines by the low-carb mania. But a recent trial, reported earlier this year and presented at the meeting yesterday, suggests that grapefruit may indeed stop weight gain by lowering insulin levels.

Meanwhile the fruit's effects on drugs could be turned into a benefit for the pharmaceutical industry. Scientists at Texas A&M Citrus Center have identified three compounds belonging to a class called furocoumarins that are responsible for inhibiting a key enzyme, CYP3A4, that metabolizes and regulates certain drugs involved in the grapefruit-drug interaction.

The researchers hope that these enzyme-blockers can eventually be developed into a ‘super-pill' or specialty grapefruit juice that can be co-administered with prescription drugs to increase their bioavailability, thus reducing dose and cost.

Roughly two-thirds of the world's grapefruit and grapefruit juice hail from Florida.