By Jennifer LaRue Huget
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.
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.
Trey Ideker, who holds posts in the schools of medicine and engineering at the University of California at San Diego, has found in laboratory tests that some limited exposure to oxidants may equip cells to better withstand larger exposures. His work, if borne out in humans, could have all kinds of implications for our understanding of aging and disease.
Most of the evidence on which antioxidants' reputation is based comes from studies of isolated cells exposed to plant chemicals or from research on rats and mice. While much of the research is compelling, none of it shows how antioxidants actually affect human health.
And those human studies may never take place, Still said in a telephone interview. "The only way to prove [antioxidants' benefits] would be to provide [subjects] a diet devoid of antioxidants, which would be very difficult, as antioxidants are fairly abundant in the food supply, or to produce a mutation in mice that [left them without] the capacity to arrest free radicals."
In any case, Britz and Still both observe that while we have a hunch that antioxidants are good for us, in fact they're not clearly essential to our health.
"They're not like vitamins," Britz notes. "They're not necessary in that you don't get a deficiency response if you don't have them." (That message is slightly blurred by the fact that some antioxidants, such as Vitamin C, are indeed vitamins that play other key roles in our bodies.)
Yet Britz and Still continue their work with lettuce. Both believe that it might lead to development of plants whose high levels of antioxidants may help them grow better and withstand the degradations of shipping and storage. And, Britz says, altering green lettuce's colors by bumping up the antioxidants might make for a prettier plant.
"If the lettuce is more attractive," he mused, "people might eat more of it -- and less of things that are bad for them."
Check out today's Checkup blog post, in which Jennifer looks at lettuce and other leafy greens. Subscribe to the Lean & Fit newsletter by going to http://www.washingtonpost.com and searching for "newsletters." And e-mail your thoughts to Jennifer at firstname.lastname@example.org.