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Amid Efforts to Give Foods More Antioxidant Punch, Mysteries Remain

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Tuesday, June 2, 2009

In a greenhouse in Beltsville, Steve Britz aims light-emitting diodes at rows of plants, hoping to coax more color out of the leaves.

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Across the country, in a lab in Pomona, Calif., David Still painstakingly manipulates plants' genetic structure, altering the DNA of some, crossbreeding others, then microscopically analyzing their progeny.

Though their approaches and technologies are as far apart as their workplaces, the two have a common goal: to build a better head of lettuce. Specifically, Britz, a research plant physiologist with the USDA's Agricultural Research Service, and Still, a professor of horticulture and plant and soil science at California State Polytechnic University at Pomona, seek to create varieties of lettuce that contain more antioxidants. (Britz is scheduled to present his research today at a conference in Baltimore.)

Antioxidants are darlings of the nutrition world, valued for their purported health-promoting and disease-busting qualities. But even as Britz and Still toil away, neither is sure antioxidants are all they're cracked up to be. In fact, the two speak in nearly identical terms about how scientists still have only a limited understanding of these substaces and how they work.

To get an idea of where the research stands, let's drop the "anti" and start with "oxidants." The body's daily functions, such as breathing and metabolizing food, and its exposure to such environmental hazards as pollution, produce stray molecules known as free radicals, which can oxidize, or interact with oxygen molecules, and damage cells.

Antioxidants can engage the free radicals before they do harm. (In their book "The Science of Good Food," David Joachim and Andrew Schloss note that the same process takes place when we rub lemon juice on an apple slice to keep it from browning: The lemon juice is the antioxidant that interrupts the oxidative process.)

Each antioxidant, from the anthocyanins and caretenoids to isoflavones and lutein, is thought to protect against a certain kind of cell damage. Ascorbic acid, or Vitamin C, and lycopene, for example, are thought to reduce DNA damage, while flavonoids (found in most fruits and vegetables) are believed to reduce the production of free radicals in the first place, and phenolics (in tea, beans and cabbage) may slow heart disease.

These chemicals, often evidenced by the bright colors they impart, also help protect plants against the ravages of excess sunlight and other environmental stresses.

One of the great mysteries about antioxidants is whether they can work in isolation, as when they are taken in dietary supplements, or whether their efficacy depends on their interactions with one another and perhaps with other substances. Another is whether they can do harm: Recent research showing that vitamins C and E, taken as supplements, may reduce the health benefits of exercise has cast a pall on antioxidant supplements.

And there's a third mystery: Is the disease-fighting capacity of fruits and vegetables directly attributable to antioxidants, or is it based on some other qualities or compounds in these foods?

Victoria Drake, a research associate at the Linus Pauling Institute at Oregon State University, put it this way in an e-mail: "Looking at the epidemiological data we have to date, we know . . . that diets rich in fruits and vegetables (antioxidant-rich foods) can reduce the risk of chronic diseases, such as cardiovascular diseases. But evidence that very high doses of individual micronutrients or phytochemicals can do the same is inconsistent and relatively weak. [As with food-based antioxidants], we would need well-controlled clinical trials to properly address the 'antioxidant hypothesis.' A healthy diet is key; supplements should be used only as 'nutritional insurance.' "

A study in the May 29 issue of the journal PLoS Genetics raises the intriguing question of whether our bodies might benefit from some exposure to free radicals.


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