I haven’t always been on the “organic” band wagon 100%. For one thing, the name is stupid. Chugging a glass of diesel fuel would be about as organic as you could get, in terms of the definition of the word I learned in high school chemistry. I am strongly in favor of sustainable farming practices that build soil, protect biodiversity, and prevent groundwater and surface water pollution. But in terms of health benefits, I have never felt the benefits were all that proven, and to some extent the industry is just based on scare tactics. I also wonder if the billions of humans on the planet can be fed without resorting to fossil fuel-derived fertilizer, and I still think that is dubious. But here is one large study in JAMA that did find significant evidence of a link between organic food (as labeled at the grocery store) and reduced cancer risk.

Association of Frequency of Organic Food Consumption With Cancer Risk: Findings From the NutriNet-Santé Prospective Cohort Study

Main Outcomes and Measures This study estimated the risk of cancer in association with the organic food score (modeled as quartiles) using Cox proportional hazards regression models adjusted for potential cancer risk factors.

Results Among 68 946 participants (78.0% female; mean [SD] age at baseline, 44.2 [14.5] years), 1340 first incident cancer cases were identified during follow-up, with the most prevalent being 459 breast cancers, 180 prostate cancers, 135 skin cancers, 99 colorectal cancers, 47 non-Hodgkin lymphomas, and 15 other lymphomas. High organic food scores were inversely associated with the overall risk of cancer (hazard ratio for quartile 4 vs quartile 1, 0.75; 95% CI, 0.63-0.88; P for trend = .001; absolute risk reduction, 0.6%; hazard ratio for a 5-point increase, 0.92; 95% CI, 0.88-0.96).

Conclusions and Relevance A higher frequency of organic food consumption was associated with a reduced risk of cancer. Although the study findings need to be confirmed, promoting organic food consumption in the general population could be a promising preventive strategy against cancer.

I researched the risk measures a little. The hazard risk ratio of 0.75 means that people eating mostly organic food (scoring in the top 25% of however they are measuring that) are 25% less likely than people eating the least organic food. That seems significant. From a quick skim, it appears they did try to control for differences in lifestyle (i.e., similar nutrition and exercise levels) and family history of cancer when coming to their conclusions.