Originally published in GMO Science
Childhood leukemia is still rare but nonetheless tops the list for the most common childhood cancer. This form of cancer is treatable with a high success rate, but health issues stemming from the treatment can develop in subsequent years. There is a significant difference in success rates between countries, depending on medical access. However, treatment protocols are costly and require sophisticated children’s health centers to administer.
Previously, some viewed childhood leukemia as a random event or as genetically predetermined. While both these factors undoubtedly play a role, new research combined with clinical evidence suggests that there is much we can do to reduce the risk of this devastating illness affecting our children and their families.
Pesticides linked with cancer
There is clearcut evidence linking pesticide exposure to childhood leukemia.  As early as 1999, an association was reported between domestic exposure to pesticides and childhood leukemia. Pre-conception exposure of the father to pesticides and the fertilizers that are generally used with them was also found to be associated with an increased risk of this disease. Out of all the pesticides and other agrochemicals studied, fungicides and fertilizers were found to pose the highest risk.
Certain commonly used pesticides have also been linked in epidemiological studies with other types of cancer. The widely used insecticide chlorpyrifos was found to be associated with an increased incidence of lung cancer in pesticide applicators.
In 2015 the cancer agency IARC classified the herbicide active ingredient glyphosate as a probable carcinogen. The verdict was based on evidence from controlled lab animal studies and also from epidemiological studies on people exposed to glyphosate-based herbicides. These are the most commonly used weedkillers worldwide and are used on around 90% of GM crops grown in the US. In addition, glyphosate-based herbicides are applied as desiccants (drying agents) prior to harvest on various non-GMO crops, especially cereals such as oats and wheat, which is why high glyphosate residue levels are present in foodstuffs derived from these grains. Furthermore, glyphosate-based herbicides are also used in gardens, parks, and public spaces. Therefore most of us are exposed to glyphosate, which explains why it repeatedly turns up in the urine of almost all US citizens who have been tested.
Regulators reassure us that these residues are present at levels below safety limits and thus will not cause harm, but this is unconvincing since we now know that very low levels of certain chemicals can cause health impacts, especially involving hormonal systems, even when higher doses appear to be safe. And a research study on pregnant women has correlated higher glyphosate levels in urine with shortened pregnancy length.
The neglected food factor
Most epidemiological studies on pesticides and cancer focus on people exposed occupationally and through domestic or on-farm use of these chemicals. But there is a severe lack of studies on the health consequences of what for most people is likely to be the longest-term and main exposure route to pesticides: residues in food.
One remarkable exception is a 2018 landmark study in French adults, which found that people who consumed organic food most regularly – with its lower pesticide content – had a lower overall cancer risk, compared to people reporting little or no consumption of organic food. The organic food eaters had a 25% lower overall cancer risk – a reduction that, if it were credited to a new cancer drug, would make global headlines. In particular, significant differences in cancer rates were found for a cancer type called non-Hodgkin lymphoma (as much as an 86% reduction) and postmenopausal breast cancer, even after accounting for factors like socioeconomic status and exercise habits.
The microbiome factor
Why would a low-pesticide-residue organic diet result in a reduced cancer risk? It’s likely that an important part of the answer lies in the gut microbiome, the community of friendly and not-so-friendly bacteria that live in our digestive tract. Research in recent years has clearly demonstrated the role of the gut microbiome in health and disease.
Starting in the first stages of life, the gut microbiome plays a key role in the development of the immune system. Newborns acquire their gut microbiome from various sites of their mother’s body, including the gut, mouth, skin, and birth canal. The acquisition of this collective of microorganisms is responsible for setting up the baby’s innate immune system. Many factors can damage this relationship, including the modern focus on “anti-microbial” living, an impoverished gut microbiome in the mother, the effects of cesarean births, antibiotic use in the mother or baby, and an absence of breastfeeding.
In addition, there is evidence that exposure to pesticides can adversely affect people’s gut microbiome.
There has been interest within health-focused circles in the fact that Monsanto (now owned by Bayer) received a patent in 2010 for glyphosate as a parasite-control antibiotic. But it is not known whether glyphosate-based herbicides, at the level to which humans are typically exposed, have an antibiotic effect on the gut microbiome. The effects of these herbicides on the human microbiome have not been studied.
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