Misconceptions About Environmental Pollution, Pesticides and the Causes of Cancer

Studies | Environment

No. 214
Sunday, March 01, 1998
by Bruce N. Ames and Lois Swirsky Gold

Misconception #4: Identification of Carcinogenic Chemicals Should Be the Primary Strategy for Preventing Human Cancer

Hormonal factors, dietary imbalances, infection and inflammation and genetic factors, none of which involve a carcinogenic chemical, are major contributors to cancer.

Deficiency of micronutrients, many of which come from fruits and vegetables, can cause cancer. Antioxidants may account for some of the beneficial effect of fruits and vegetables, as discussed in Misconception #2. However, the effects of deficiency of dietary antioxidants are difficult to disentangle by epidemiological studies from that of other important vitamins and ingredients present in fruits and vegetables.31

Folate deficiency, one of the most common vitamin deficiencies, causes extensive chromosome breaks in human genes.32 Approximately 10 percent of the US population33 has a lower folate level than that at which chromosome breaks occur.34 In two small studies of low income (mainly African-American) elderly35 and adolescents36 nearly half had folate levels that low. The rate of chromosome breaks in humans is reduced by folate administration.37 Chromosome breaks could contribute to the increased risk of cancer and cognitive defects associated with folate deficiency in humans. 38 Folate deficiency also damages human sperm,39 causes neural tube defects in the fetus and about 10 percent of U.S. heart disease.40 Diets deficient in fruits and vegetables are commonly low in folate, antioxidants, (e.g., vitamin C) and many other micronutrients, and result in DNA damage and higher cancer rates.41

Many other micronutrients whose main dietary sources are other than fruits and vegetables, also are likely to play a significant role in the prevention and repair of DNA damage, and thus are important to the maintenance of long term health. Deficiency of vitamin B12 (found in 5 percent of the U.S. population) causes a functional folate deficiency, accumulation of homocysteine (a risk factor for heart disease)42 and probably causes chromosome breaks.43 Strict vegetarians are at increased risk of developing a vitamin B12 deficiency.44 Niacin contributes to the repair of DNA breaks.45 As a result, dietary insufficiencies of niacin (15 percent of some populations are deficient)46, folate and antioxidants may act together to increase DNA damage. There is also some evidence that deficiencies of zinc, copper, iron, selenium and vitamin B6 (each deficiency occurs in 5 to 20 percent of the population), can lead to DNA damage.47 Optimizing micronutrient intake (through better diets, fortification of foods or multivitamin-mineral pills) can have a major impact on health at low cost. Increasing research in this area, and efforts to increase micronutrient intake and more balanced diets, should be high priorities for public policy.

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