Led by Julia Baudry, an epidemiologist at Institut National de la Sante et de la Recherche Medicale in France, a team of researchers looked at the diets of 68,946 French adults. More than three-quarters of the volunteers were women, in their mid-40s on average. These volunteers were categorized into four groups depending on how often they reported eating 16 organic products, including fruits and vegetables, meat and fish, ready-to-eat meals, vegetable oils and condiments, dietary supplements and other products.
Follow-up time varied for each participant but lasted slightly more than four and a half years on average, and during that time, the study volunteers developed a total of 1,340 cancers. The most prevalent was breast cancer (459) followed by prostate cancer (180), skin cancer (135), colorectal cancer (99), and non-Hodgkin lymphomas (47).
The authors calculated cancer risk
Comparing the participants' organic food scores with cancer cases, the researchers calculated a negative relationship between high scores (eating the most organic food) and overall cancer risk. Those who ate the most organic food were 25% less likely to develop cancer. Specifically, they were 73% less likely to develop non-Hodgkin lymphoma and 21% less likely to develop post-menopausal breast cancer.
Even participants who ate low-to-medium quality diets yet stuck with organic food experienced a reduced risk of cancer, the authors found.
The authors theorize a "possible explanation" for the negative relationship between organic food and cancer risk stems from the "significant" reduction of contamination that occurs when conventional foods are replaced by organic foods.
"If the findings are confirmed, promoting organic food consumption in the general population could be a promising preventive strategy against cancer," Baudry and her colleagues concluded.
Dr. Jorge E. Chavarro, an associate professor in the Department of Nutrition at Harvard T.H. Chan School of Public Health, said in a podcast that the new study is "incredibly important." He co-authored a commentary published with the study.
Most people who are not employed in agriculture are exposed to pesticide residues through food, said Chavarro, who was not involved in the study.
The new findings are consistent with those of the International Agency for Research in Cancer, which found pesticides are cancer causing in humans, noted Chavarro. They also align with those of another study that showed a negative relationship between eating organic food and non-Hodgkin lymphoma, he said.
However, Chavarro added that researchers designing future studies should be mindful of certain limitations in this new study.
Drawbacks of the study
"Assessing intake of diet is difficult, assessing intake of organic foods is notoriously difficult," said Chavarro. "That is because deciding to eat organic foods or not is a decision that has very strong social and economic determinants. Even though the authors had access to information of why people are choosing not to eat organic foods, they consider all non-consumers of organic foods the same."
For example, people who choose not to eat organic despite being able to afford to do so might have a poor attitude toward their health in general and that would likely influence the results.
Chavarro also said it is unclear that quantifying organic food consumption is really calculating what the study authors want to measure -- reduced exposure to pesticide residues through diet.
It's true that previous research, including one of Chavarro's own studies, have shown a correlation between organic food consumption and pesticide levels in urine, so the assumption is not incorrect. Still the authors need to show this, he said in the podcast about the study. And, different conventional foods are more "dirty" (contaminated with pesticides) than others, he said, so eating certain organic foods does a better job of protecting us against ingesting pesticides than others. Yet the study does not do a good job of sorting and evaluating these differences, he noted.
"At the current stage of research, the relationship between organic food consumption and cancer risk is still unclear," Chavarro and his co-authors wrote in the commentary.
In the end, the study's takeaway, according to Chavarro, is that we should all probably be paying more attention to how much organic food we eat and "we should probably be studying this more."
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