By Janet Raloff

Web edition: February 14, 2001

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Citrus fruits may deserve a more prominent role in the diet. A research team in Canada has just shown that drinking several glasses of orange juice daily can pump up blood concentrations of the so-called good cholesterol.

Boosting this high-density-lipoprotein (HDL) cholesterol can slow the buildup of artery-clogging plaque (SN: 9/9/89, p. 171).

In their study, Elzbieta M. Kurowska and her colleagues at the University of Western Ontario in London, Ontario, monitored changes in cholesterol concentration and related blood chemicals in 16 men and 9 women for 23 weeks. The middle-age volunteers were healthy but had moderately elevated total-cholesterol concentrations in their blood.

During the first 6 weeks, each volunteer adopted a cholesterol-lowering diet--one based on American Heart Association guidelines. In the seventh week, the participants began drinking a quarter-liter cup of orange juice daily. Four weeks later, they upped consumption to two cups daily. In the next 4-week phase, all downed three cups of juice a day. Finally, the scientists asked the volunteers to stop drinking the juice but maintain a heart-healthy diet for 5 more weeks.

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Blood concentrations of the so-called bad--or low-density-lipoprotein--cholesterol remained unchanged, Kurowska's team reports in the November 2000 American Journal of Clinical Nutrition. However, compared with the starting values, HDL cholesterol concentrations in the volunteers climbed 5 percent when they downed a cup of juice daily, settled at 7 percent higher on two cups per day, and jumped to 21 percent higher during the three-cups-a-day phase.

"An even bigger surprise was that HDL cholesterol stayed high 5 weeks after the treatments ended," Kurowska says. In fact, it reached 27 percent above starting values. What's more, she found signs that the HDL incorporated more of a protein building block called apo-A4 than it had originally. Apo-A4 protects against heart disease, says Kurowska.

Tropicana Products of Bradenton, Fla., which funded the research, has financed a follow-up study at the Cleveland (Ohio) Clinic preventive-cardiology unit, notes Carla McGill, who heads nutrition science for Tropicana.

Earlier, Kurowska showed that certain orange-juice constituents called liminoids could trigger heart-healthy lipoprotein changes in cultured human cells. Last year, her group published related test-tube findings on another class of citrus compounds. They found that the flavonoids hesperetin and naringenin in orange and grapefruit juice both cut cholesterol synthesis. However, Kurowska says her latest data indicate tangerines may offer cholesterol-modulating flavonoids that are even more effective.

It's important to remember that the new data show that people must consume large quantities of juice or fruit to get a beneficial cholesterol effect, observes James Cerda of the University of Florida in Gainesville.

Unfortunately, the orange juice raises blood concentrations of sugar. Concern over how to safely deliver enough of the active agents has prompted Myung-Sook Choi of Kyungpook National University in Taegu, Korea, and her colleagues to begin developing dietary supplements or drugs based on citrus flavonoids.

With Song-Hae Bok of the Korea Research Institute of Bioscience and Biotechnology in Taejon, Choi reported in the June 1999 Journal of Nutrition that the tangerine flavonoids naringin and hesperidin offer potent cholesterol-lowering action in animals. Though both flavonoids occur in juice, the peel offers the richest source. In fact, Choi's team obtained a U.S. patent earlier this year for using tangerine flavonoid combos to elevate people's HDL-cholesterol concentrations.

Kurowska, however, notes there may be an alternative to such supplements. Eat a variety of fruits and vegetables, she advises.