Vitamin C protects blood from radicals.

Vitamin C protects blood from radicals

Ascorbate, better known as vitamin C, appears the premier blood agent responsible for disarming reactive chemicals called free radicals, according to new laboratory research. At levels typically found circulating in human blood plasma, the vitamin neutralized 100 percent of the free radicals produced in the study. No other plasma antioxidant, or free-radical "quencher," showed this capability.

Because other research has shown that free-radical damage of blood fats carried by low-density lipoproteins (LDLs) helps initiate artery-clogging plaque, the new findings also indicate that adequate vitamin C nutrition "might have the potential to protect against atherosclerosis," says biochemist Balz Frei of the University of California, Berkeley, who led the work.

"I was quite surprised at how much better a scavenger of free radicals and oxidants ascorbate was, especially when compared with vitamin E," says Frei. Scientists generally view tocopherol, or vitamin E, as the body's premier antioxidant. But tocopherol protected only about 70 percent of the LDL lipids from free radicals, whereas ascorbate protected them all, Frei notes. "And that 30 percent [of blood fats] tocopherol does not protect means that you risk considerable pathologically relevant damage," he says.

Frei and his co-workers isolated plasma from human blood, incubated it at body temperature and added a chemical that initiates free radicals as it decomposes at such temperatures.

In addition to ascorbate, plasma contains three other water-soluble antioxidants -- protein thiols, bilirubin and urate--but when ascorbate was present, it alone disarmed the radicals, conserving the other antioxidants, the researchers report in the August PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES (Vol.86, No.16). And even though tocopherol -- a fat-soluble anti-oxidant -- resides in LDLs, when Frei's team allowed free radicals to overwhelm the ascorbate and use it up, the radicals succeeded in oxidizing nearly a third of the LDL lipids.

These observations suggest that while other plasma antioxidants can slow lipid oxidation, "only ascorbate can completely prevent it," Frei says. He and his colleagues think their data argue for increasing the recommended daily allowance for vitamin C -- a level presently based only on the vitamin's role in preventing scurvy.