Huge French study linked predominantly organic diets to a 25% overall reduction in cancer risk
Many people assume that organically produced foods are safer and more nutritious.
That presumption seems logical and is backed up by substantial, albeit mixed and inconclusive, evidence.
The most recent evidence review examining studies on the comparative nutritional value of organic foods was reported in 2012 by scientists from Stanford University, who analyzed the results of 237 studies.
We covered that review in Organic Food Gets a Mixed Review, which contains links to our prior reports on studies of the comparative nutritional value of organic foods.
The Stanford team’s evidence-review covered 17 studies in which people consumed organic and conventional diets. They included six randomized clinical trials that lasted from just two days up to two years — not long enough to detect significant differences in health outcomes.
And unfortunately, we still lack any long-term studies examining health outcomes among people who consume predominantly organic diets versus predominantly conventional diets.
The other 200-plus other studies covered in the Stanford review compared the nutrient and/or contaminant levels of various foods — fruits, vegetables, grains, meats, milk, poultry, and eggs — grown using organic or conventional methods.
Most media stories about the Stanford review focused on the finding of a lack of clear evidence that organic foods offer nutrient advantages, and downplayed its affirmation of other health advantages.
For example, the Stanford team’s review confirmed that organic fruits and vegetables are higher in beneficial antioxidants, and that children on organic diets have lower levels of pesticides in their bodies.
Large British population survey found no overall cancer benefits
In 2014, researchers from the UK reported the results of the “British Million Women” study, which included a single question about how often a participant ate organic foods.
That study detected a somewhat lower risk of non-Hodgkin’s lymphoma — but higher breast cancer rates — among women who said they usually or always ate organic food. And the results didn’t link predominantly organic diets to a reduction in overall cancer risk.
Now, the results of a very large, better-designed French study add important — but still inconclusive — evidence that diets high in organic foods may reduce the risk of major cancers.
French study of predominantly organic diets links them 25% less cancer
The just-published study was conducted by French researchers from the Sorbonne, the Universities of Marseille and Paris, two hospitals, and France’s counterparts to the U.S. NIH and USDA (Baudry J et al. 2018).
For their seven-year study, they recruited 68,946 volunteers, 78 percent of whom were women, whose average age at the outset of the study in May of 2009 was 44 years.
The participants answered detailed questions about how often they consumed organically produced versions of more than 20 different types of food, including fruits, vegetables, dairy foods, soy foods, meat, fish, eggs, grains, legumes (e.g., beans), bread, cereals, flour, oils, and more.
Each volunteer provided three 24-hour records of their intake of these foods, including portion sizes, over a span of 14 days.
They also reported their intake of alcohol and provided information about factors relevant to cancer risk, including: age, sex, physical activity, height, weight, use of supplements, sun exposure, occupational status, educational level, marital status, monthly income, number of children, and smoking status.
Finally, researchers had access to the health records of the volunteers at the beginning and end of the seven-year study, which lasted until November 30, 2016.
After comparing the participants’ self-reported diets to their health status at the end of the study, the French team found that those who reported eating organic foods the most frequently had 25% fewer cancers, compared to those who never ate organic foods.
In addition, the participants who reported eating the most organic foods were much less likely to have developed lymphoma-type cancers and had a significantly lower rate of postmenopausal breast cancers.
In 2015, the International Agency for Research on Cancer (IARC) — which is part of the UN's World Health Organization — classified some commonly used synthetic pesticides and herbicides as probably carcinogenic (malathion and diazinon), and others as possibly carcinogenic (tetrachlorvinphos and parathion).
More recently, the IARC found evidence that glyphosate — the active ingredient in Monsanto's Roundup herbicide — is a possible carcinogen. However, that conclusion is contradicted by assessments from the European Food Safety Authority, the U.S. Environmental Protection Agency, and the World Health Organization itself.
Given the lack of research into the effects of exposure to multiple pesticides and herbicides, the French team called for more research into links between diet-related exposure and cancer risk:
“While there is a growing body of evidence supporting a role of occupational exposure to pesticides for various health outcomes and specifically for cancer development, there have been few large-scale studies conducted in the general population, for whom diet is the main source of pesticide exposure.”
And they called for further research to identify why — including or in addition to reduced pesticide exposure — organic foods would reduce the risk of cancer versus conventional foods.
Harvard researchers provided critiques in an invited commentary
The publishers of JAMA — the journal that published the French study — asked prominent epidemiological researchers from Harvard University to comment on its design and conclusions (Hemler EC et al. 2018).
The Harvard scientists noted two basic weaknesses of the study:
- People’s answers to diet surveys are unreliable.
- The researchers didn't test the participants' pesticide levels, which would have shown whether diets rich in organic foods yielded lower levels and help explain why such diets would reduce cancer rates.
Testing the participants’ bodies for pesticide levels might’ve been prohibitively expensive, versus doing that in a smaller-scale study.
The authors of the new study presumed that higher self-reported intake of organic foods translated into lower exposure to pesticide residues. However, as the Harvard commentators said, people's answers to questions about the proportions of organic foods in their diets don't always predict their body levels of pesticides.
Overall, the Harvard scientists concluded that the subject requires further, more reliable research, and that the benefits of eating conventionally grown produce outweigh the potential cancer risks.
They also noted that organic foods usually cost considerably more, making them virtually inaccessible to lower-income people, which is obvious but seems beside the point.
If the anti-cancer — and ecological — benefits of predominantly organic diets can be proven beyond doubt, then it will behoove society to devise ways to reduce the cost of organic foods.
The environmental benefits of organic agriculture
You'd think that ecological benefits of organic farming are clear, but that’s not exactly the case.
While some independent (not funded by agribusiness) analyses find that organic farming has clear environmental benefits, others have failed to find a clear advantage — other than the important benefit of protecting farmers, farmworkers, and wildlife from harmful chemicals.
Two years ago, British researchers published their review of European studies concerning the environmental impacts of organic versus conventional farming, which echoed those of similar reviews.
As they wrote, “Most of the studies … demonstrated lower environmental impacts from organic farming. The key challenges in conventional farming are to improve soil quality (by versatile crop rotations and additions of organic material), recycle nutrients and enhance and protect biodiversity. In organic farming, the main challenges are to improve the nutrient management and increase yields.” (Kniss AR et al. 2016).
And there remains significant uncertainty about the relative productivity of organic versus conventional farming — some studies find that organic methods can match the output of conventional methods, while others find that organic methods produce about 20% less food overall.
Getting a solid answer to the question of productivity is critical, because if broad adoption of organic farming methods resulted in a significant drop in food production, that would have serious implications for food supplies worldwide.
Conversely, conventional agriculture relies heavily on petroleum-derived synthetic fertilizers, while fertilizer and pesticide runoff are doing serious damage to rivers lakes, and oceans — impacts with negative implications for the overall environment.
That said, studies have found that fertilizer (e.g., manure and compost) runoff from organic farms can be a significant source of water pollution.
So far, the acreage devoted organic farms is so small that this is a minor problem, but it could grow along with the proportion of agricultural land farmed organically.
- Baudry J et al. Association of Frequency of Organic Food Consumption With Cancer Risk: Findings From the NutriNet-Santé Prospective Cohort Study. JAMA Intern Med. Published online October 22, 2018. doi:10.1001/jamainternmed.2018.4357
- Hemler EC, Chavarro JE, Hu FB. Organic Foods for Cancer Prevention—Worth the Investment? JAMA Intern Med. Published online October 22, 2018. doi:10.1001/jamainternmed.2018.4363
- Kniss AR, Savage SD, Jabbour R. Commercial Crop Yields Reveal Strengths and Weaknesses for Organic Agriculture in the United States. PLoS ONE 11(8): e0161673. Published: 23-Aug-2016. doi: 10.1371/
- Meier MS, Stoessel F, Jungbluth N, Juraske R, Schader C, Stolze M.Environmental impacts of organic and conventional agricultural products--are the differences captured by life cycle assessment? J Environ Manage. 2015 Feb 1;149:193-208. doi: 10.1016/j.jenvman.2014.10.006. Epub 2014 Nov 9.
- Tuomisto HL, Hodge ID, Riordan P, Macdonald DW. Does organic farming reduce environmental impacts?--a meta-analysis of European research. J Environ Manage. 2012 Dec 15;112:309-20. doi: 10.1016/j.jenvman.2012.08.018. Epub 2012 Sep 1.