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Human Health Implications of Genetically Modified Crops (excerpt from Sustaining Life)


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The potential benefits for human health from GM crops over conventional crops are several, although such comparisons should also be made between GM and other agricultural practices, such as organic farming. If growing GM crops results in the reduced use of toxic chemicals, or a switch to chemicals of lower toxicity, that would be beneficial, given the potential role of some pesticides in causing human disease, especially among infants and children. If significantly greater yields were achieved by using GM technologies, particularly in the developing world, where risk for crop failures because of extreme weather events secondary to climate change will be ever more likely in the coming century, the public health benefits would be enormous. If the nutritional quality of foods could be improved, for example as has already been done with rice to relieve vitamin A deficiency (a condition that afflicts some 400 million people worldwide), great strides in relieving human suffering would be made. 

But, there are also potential risks. For one, there are the risks that could come from pharmaceutical production in food crop species. The so-called “pharma crops” are grown according to stringent protocols designed to prevent contamination of the food supply. For example, corn that has been genetically engineered to produce drugs such as lactoferrin (an antimicrobial, iron-binding protein, present in high concentrations in human colostrum--the first breast milk secretions) is required by the USDA to be grown at least one mile away from other cornfields. After harvest, such “pharma” corn must be labeled and carefully tracked to avoid mixing it with corn destined for consumption by either humans or livestock. However, scores of recent examples of human error in dealing with GM crops suggest that contamination of food with “pharma crops” is a likely occurrence.

The use of antibiotic resistance genes as markers in GM crops has also raised human health concerns, as such genes could potentially be transferred to bacteria that live in the intestines of cattle and other livestock and in the human gastrointestinal tract and be difficult to treat with antibiotics. Although several scientific reviews have concluded that there is little to no chance of such gene transfer, the editors of this volume believe that using a gene marker that carries a potentially significant human health risk, particularly at a time when we are facing a growing crisis of antibiotic resistance, even if its transfer is extremely unlikely to occur, should be strongly discouraged. This position has been taken by the United Kingdom’s Royal Society, which stated “any further increase in the number of antibiotic-resistant microorganisms resulting from transfer of antibiotic-resistance markers from GM foods should be avoided” , and by the Expert Group of the Medical Research Council of the U.K., which has recommended that antibiotic resistance genes be removed from GM foods, even though they considered the possibility of such transfer to be remote. 

Another possible human health consideration that has been raised is that potential toxins or allergens could be produced via the transgene itself, or that such compounds might arise inadvertently via other changes in plant chemistry, caused by the action of inserted gene switches and gene promoters, or by the accidentally altered functioning of host organism genes. This remains a concern, but the potential for GM food allergens has been made less likely by the current practice that prohibits the transfer of genes encoding known allergens or of those from particularly allergenic species.

There is also the possibility that one of the chemicals widely used in GM crops, glyphosate, and perhaps to an even greater extent, its commercial preparation Round-upâ, may act as an endocrine disruptor. A recent study has shown that glysophate disrupts in human placenta cells the gene expression and activity of the enzyme aromatase, which is responsible for the synthesis of estrogen, at concentrations that are 100 times lower than those recommended for use in GM crops. The addition of surfactants (these are wetting agents that are used to allow easier spreading of a liquid) in Round-upâ amplified these toxic effects, perhaps because these chemicals facilitated the entry of glyphosate into cells. At higher doses, still below concentrations that are used in agriculture, the toxicity of glyphosate to placental cells could result in human reproduction problems.

As more than 44 million tons of glyphosate are used in the U.S. each year (1999 figures), and by very rough extrapolation, approximately double that figure or more globally (given the proportion of U.S. to global GM acreage), exposing millions of agricultural workers, and as glyphosate may persist in soils and contaminate some freshwater ecosystems, thereby entering the water supply and the food chain, we need to have a much better understanding than we do of its potential effects on human health.effects on human health.

Aaron Bernstein, MD, MPH

Aaron Bernstein is the Interim Director of The Center for Climate, Health, and the Global Environment, a pediatrician at Boston Children’s Hospital, and an Assistant Professor of Pediatrics.

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