The Optimum Level of Antioxidants

The epidemiological evidence and the guidelines of the National Cancer Institute and the National Research Council/National Academy of Sciences suggest that at least two fruits and three vegetables per day is a desirable intake.

Since ascorbate, tocopherol, and ß-carotene supplements are inexpensive and high doses are remarkably non-toxic, there is a school that believes that supplements, in addition to a diet containing recommended levels of fruits and vegetables, are desirable.

There is suggestive, but inadequate epidemiological and biochemical evidence bearing on the question. What is clear is that fruits and vegetables contain many necessary micronutrients in addition to antioxidants, some of which also can prevent mutations. Folic acid, for example, is required for the synthesis of the nucleotides in DNA.

Inadequate intake has been shown to cause chromosome breaks and increased cancer and birth defects. Folate deficiency may be a risk factor for myocardial infarction as well. Niacin is required for making poly (ADP-ribose), a component of DNA repair. Other micronutrients are also likely to be part of our defense systems.

The U.S. Recommended Daily Allowances (RDAs) for ascorbate and tocopherol intake--there is no guideline for [[beta]]-carotene independent of its provitamin A activity--are not adequate for several reasons:

1) The amount recommended, e.g., 60 mg/day for ascorbate, is primarily for avoiding an observable deficiency syndrome, e.g., scurvy, and is not necessarily the amount for optimum lifetime health, which is usually not known.

2) A recommended blood level of each antioxidant, e.g., 60 uM ascorbate, would be a more desirable standard. People vary considerably in the intake required to keep their blood level adequate. A smoker, for example, needs to take in several times as much ascorbate as a non-smoker to keep the blood level the same.

Infections may also cause an oxidative stress that leads to antioxidant depletion by activating phagocytic cells. The observation that antioxidant inadequacy is associated with oxidative damage to DNA of the germ line as well as somatic cells, emphasizes the urgency of defining adequate blood levels.

Since only 9% of Americans, and fewer in most other countries, are eating five fruits and vegetables per day, there is a great opportunity to improve health by increasing consumption.

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