Does choosing organic over conventional foods protect against cancer? What are the effects of pesticides on cancer risk?
In a review updating the evidence on human exposure and toxicity of pesticides, the body of evidence linking pesticide exposure and cancer is said to be so massive that pesticides’ role in the development of cancer “cannot be doubted.” However, most of the evidence that shows DNA damage from pesticides is from occupational exposure among farmers and workers in the fields, the pesticide industry itself, or those living in high-spray areas, as you can see at 0:35 in my video Pesticides and Cancer Risk.
There is evidence linking non-occupational pesticide exposure to DNA damage—in this case, single- and double-stranded DNA fragmentation in the sperm of men with higher levels of pesticides flowing through their bodies—but that was in China, where the average pesticide concentrations are as much as four times higher than in some other parts of the world.
Another way pesticides could potentially facilitate tumor growth is through adverse effects on anticancer immunity. Natural killer (NK) cells are our body’s first line of white blood cell defense against cancer cells and virus-infected cells. Pesticides have been shown to induce harmful effects on these defender cells, reducing their ability to kill off tumor cells. For example, if you put a bunch of NK cells in a petri dish along with human leukemia cells without any pesticide, your natural killer cells can clean house and wipe out more than half the cancer. But if you drip a tiny bit of pesticide on them, the NK cells are so disabled that the cancer wins the day, as you can see below and at 1:37 in my video.
But how much pesticide are we talking about? The researchers used the maximum level found in people actively spraying pesticides. But what about looking at just the residual pesticides left on conventional produce? Is choosing organic for cancer prevention worth the investment?
Pesticides are detectable in the blood and urine of more than 90% of the U.S. population, regardless of where they work or live. We know it’s from the food we eat because crossover trials where people are switched between consuming conventionally grown foods and organic foods show you can turn on and off urinary concentrations of pesticide metabolites like a light switch. But that doesn’t necessarily mean the pesticides are harming us.
The health consequences of ingesting pesticide residues from conventionally grown foods remain unknown, but a recent study did find that people who self-reported the highest frequency of organic food consumption had about a 25% lower risk of getting cancer. The study is the first of its kind to evaluate the association between frequency of organic food consumption and cancer risk, controlling for a wide array of other factors. Doesn’t it matter that consumers eating organic are younger? The researchers controlled for that and still found significantly lower cancer risk. But maybe organic consumers get less cancer because they are more affluent or more highly educated or skinnier, or maybe they exercise more or eat less meat or smoke less. No, the researchers controlled for all that and still found significantly lower cancer risk in organic consumers. Maybe their diets were different in other ways, though—more fruits and vegetables overall, or less junk food? No, they still found significantly lower cancer risk. The researchers concluded, “Our results indicate that higher organic food consumption is associated with a reduction in the risk of overall cancer.”
That was the most sophisticated study of its type to date, but there was an earlier study that was even bigger, and little evidence was found for a decrease in the incidence of all cancers except for perhaps one kind of blood cancer—non-Hodgkin lymphoma. You can see the data below and at 3:59 in my video.
The data show no difference in cancer overall between those who never choose organic and those who usually or always do; the only significant findings were a lower risk of non-Hodgkin lymphoma and an increased risk of breast cancer. Is it possible that women who choose organic food are more conscientious about getting screened for breast cancer, and that explains the higher diagnosis rate? We really don’t know.
Of course, what we care about the most is not just cancer but all-cause mortality—the risk of dying prematurely. As it turns out, higher blood levels of a pesticide known as beta-hexachlorocyclohexane are associated with living a significantly shorter life. How do we cut down on our levels? Decades ago, there was a study that found that the breast milk of a vegetarian mother had less beta-hexachlorocyclohexane than the milk of her non-vegetarian sister, who was also breastfeeding at the time. The vegetarian sister apparently had levels of that pesticide that were lower by about a third, compared with her omnivorous sibling, as you can see below and at 4:48 in my video.
That’s no surprise, since this class of chlorinated pesticides is fat-soluble, so they’re found most frequently in foods of animal origin.
A more recent study failed to look at beta-hexachlorocyclohexane, but it examined polychlorinated biphenyls (PCBs) and found that they were linked to increased mortality risk. Again, the toxins were found in the same kinds of foods: eggs, dairy products, and animal fats. So, it’s no surprise that the blood of those eating vegan was found to be “significantly less polluted than omnivores” in terms of a whole series of PCBs, including those found in the study to be associated with increased mortality; but the vegans did not have lower levels of beta-hexachlorocyclohexane.
The bottom line: If you’re worried about the adverse health effects of pesticides and pesticide-type compounds, you may want to lower your intake of animal products. But when it comes to fruits and vegetables, the benefits of eating conventionally grown produce likely outweigh any possible risks from pesticide exposure. So, concerns about pesticide risks shouldn’t discourage us from stuffing our faces with as many fruits and vegetables as possible. That would give us a huge health benefit, whereas the potential lifelong damage of any pesticides on those same fruits and veggies has been estimated to cut only a few minutes off a person’s life, on average, which is nothing compared to the nutritional benefits of eating more fruits and vegetables.
Doctor’s Note
For more on organic foods, see related posts below.
