Antioxidants and Beta Carotene

IN the last few years, the word "antioxidant" has moved rapidly from the domain of chemists and biochemists into common use, at least among health-conscious Americans. Millions of people concerned about preventing heart disease and cancer and staving off the ravages of age have turned to antioxidant nutrients like vitamins C and E, beta carotene and selenium as if they provided a protective cloak against both self-inflicted and environmental insults.

Medical researchers, too, have jumped on the antioxidant bandwagon, undertaking huge studies to see whether and how well antioxidants might guard against the damage wrought by such noxious influences as cigarette smoke, fatty diets, air pollution and a host of inescapable carcinogens.

The idea behind antioxidants is to block the action of omnipresent free radicals, highly reactive oxidizing substances that form in the body during normal metabolism and that enter the body from the external environment. Cigarette smoke and polluted air, for example, contain many of these oxidizing substances. Oxidation, the chemical process that makes iron rust, can wreak havoc in the body as well.

Setting Off Cancer Process

For example, oxidation reactions caused by free radicals can damage cell membranes that protect tissues against noxious agents like toxins and carcinogens. Free radicals can change some substances that are potential carcinogens into a form that can initiate the cancer process.

Free-radical damage is thought to be an important contributor to the bodywide deterioration that accompanies aging. And recent studies have shown that LDL cholesterol, the so-called bad cholesterol, is changed through oxidation from a form that circulates freely in the blood to a form that can latch onto artery walls, narrowing their passageway and thus increasing the risk of heart attack and stroke.

Considerable circumstantial and laboratory evidence suggests that nutrients with antioxidant properties can at least partly protect against such damage. For example, studies done in university laboratories in Texas and California showed that vitamins C and E can prevent the oxidation of LDL cholesterol, therefore presumably reducing the risk of cardiovascular disease.

Two very large studies, one involving 40,000 men followed for four years and the other 80,000 women who were followed for eight years, revealed that those who took daily supplements of vitamin E averaging 200 to 400 international units were 40 percent less likely than those who did not take the supplements to develop heart disease during the study period.

A British study among 110 patients with angina (chest pains caused by insufficient oxygen to the heart muscle) and 394 men free of angina found that in those with low blood levels of vitamin E, the risk of developing angina was nearly three times as high.

A Surprising Finding

And a continuing study among 22,000 American male doctors yielded a surprising interim finding: those taking a supplement of beta carotene to test the nutrient's anticancer potential suffered only half the expected number of serious cardiovascular events, like heart attacks and strokes.

The possibility of an anticancer effect of foods rich in beta carotene has been suggested by a number of long-term studies. For example, in a study begun in 1958 in Chicago among 2,100 men, those with a low intake of foods containing carotene were more likely to have died of lung cancer 19 years later.

In a Swiss study of nearly 3,000 men begun in 1971, cancer deaths were significantly higher among those with low levels of carotene and vitamin C in their blood. Low levels of carotene were especially associated with a greater risk of lung cancer, and low levels of vitamin C were linked to an increased risk of cancers of the stomach and intestines. In studies of women with precancerous changes in the cervix, abnormal tissues were far more commonly found in those with low blood levels of beta carotene and vitamin C.

But in all these cancer studies the possible beneficial effects observed were associated with the consumption of foods rich in antioxidants, not supplements. Such foods contain many potentially beneficial substances in addition to beta carotene and vitamin C, and it is not possible to say whether the apparent protection against cancer is attributable to any one substance or even to these foods per se. Rather, it is possible -- in fact, likely -- that people who eat lots of wholesome foods like fruits and vegetables rich in beta carotene and vitamin C also practice other good health habits that lower their cancer risk.

To control for this possibility, long-term studies must be conducted among large numbers of people who are randomly assigned to take either the nutrient in question or a look-alike dummy pill. Such a study has yet to be completed, particularly among people who do not smoke.