Credit: CC0 Public DomainTo reduce the risk of cancer, you know that you should quit smoking, exercise regularly, wear sunscreen…
Credit: CC0 Public Domain
To reduce the risk of cancer, you know that you should quit smoking, exercise regularly, wear sunscreen and take advantage of screening tests. New research suggests that another item may be added to this list: Choose organic foods over conventional.
A study of nearly 70,000 French adults traced on average 4.5 years found that those who ate the most organic foods were less likely to develop certain types of cancer than those who ate the least.
Due to the way in which the study was conducted, it is impossible to say that the organic foods that people ate were the reason they had fewer cases of cancer. But the results are big enough to motivate follow-up studies, researchers wrote.
“Further research is required to identify which specific factors are responsible for potential protection effects of organic food consumption on cancer risk,” wrote JAMA Internal Medicine on Monday.
The researchers have an idea of what factors they can be: pesticides. At least three of them ̵
1; glyphosate, malathion and diazinone – are likely to cause cancer, and others may be carcinogenic, according to the International Cancer Research Agency.
“Organic products are less likely to contain pesticide residues than conventional foods,” they wrote. This is because the rules that farmers must follow to use the organic label usually prohibits the use of synthetic pesticides (although pesticides based on natural compounds such as hydrogen peroxide and soaps are allowed).
Previous studies have shown that pesticide residues are more common on conventionally grown products than on its organic counterparts. For example, a report from this year from the European Food Safety Authority found residues from one or more pesticides of 44 percent of the conventionally produced food samples tested. Meanwhile, 6.5 percent of the tested organic food samples had detectable pesticide residues.
And there is evidence that these pesticides are metabolized in the body. Urine in people who eat some (if any) organic foods contain higher concentrations of pesticide chemicals than urine in people who regularly eat organic foods.
In the United States, more than 9 out of 10 people have measurable amounts of pesticides in their urine or blood, and these concentrations are known to fall when people switch from conventionally produced food to organic.
Consumption of fewer pesticide-related chemicals really seems like a good idea. But if it is associated with a real health distribution, it is unclear.
So a team from Inserm, the French equivalent of the US National Institutes of Health, was looking for data.
In an ideal world, they would recruit thousands of volunteers and randomly divide them into two groups: one that follows an organic diet and one who does not. They would supervise these volunteers to ensure that they retained their assigned diets and observe the other things they do that can affect their cancer risk. Then after many years they would figure out the number of cancers diagnosed in each of the groups and see if there was a difference that could only be explained by the amount of organic food they ate.
But this is not an ideal world, so researchers have to do with the data that were available.
They focused on people who joined a comprehensive ongoing health and nutrition study that began in 2009. They were questioned about 16 categories of food, including fruits, vegetables, eggs and wine – and how often the organic versions of them. Once a year they gave health updates, including whether they had been diagnosed with cancer.
By the end of 2016 there were 68,946 French adults who met all of these criteria and were included in the analysis. Their average age when they joined the study was 44, and 78 percent of them were women.
Between 2009 and 2016, cancer was diagnosed in 1 340 by volunteers. The most common type was breast cancer (459 cases) followed by prostate cancer (180 cases), skin cancer (135 cases), colorectal cancer (99 cases), non-Hodgkin’s lymphoma (47 cases) and other types of lymphoma (15 cases) .
The writers ranked the volunteers according to how often they ate organic foods and divided them into four equal groups. This revealed that the people who ate organic food usually had higher incomes, more education and higher jobs. They were also more inclined to exercise, to quit smoking, and to eat higher amounts of healthy foods like fruits and vegetables. All of these things are associated with a lower risk of cancer.
After taking into account these and other demographic factors, they found that the most often organic food was 25 percent less likely to develop any type of cancer than those who ate at least organic food. The overall effect of choosing a lot of organic foods was as great as having a family history of cancer.
When they considered each type of cancer separately, they found that only three had a statistically significant association with organic food consumption.  One of them was postmenopausal breast cancer: The women who ate organic foods were usually 34 percent less likely to get this diagnosis than women who ate at least organic foods. (There were also tips on reduced risk of premenopausal breast cancer, but the difference was less and could have been a chance.)
Another was non-Hodgkin’s lymphoma: The most common eats of organic food were 86 percent less likely to get this form of cancer than its counterparts at the other end of the spectrum. The difference between the two groups was barely large enough to be statistically significant.
The last category was all lymphoma: People who usually ate organic foods were 76 percent less prone to receiving lymph node than people who ate organic foods at least.
Some of these results were in line with previous studies, and some were not. In particular, the French researchers compared their findings with data from the Million Women Study in Britain. In the Million Women Study, participants who ate organic food regularly had a 21 percent lower risk of non-Hodgkin’s lymphoma than participants who did not eat organic food at all. However, there was no reduction in total cancer risk and the risk of breast cancer was slightly higher in women who regularly ate organic food than for women who did not eat it at all.
“It now seems important to evaluate the chronic effects of low dose exposure of pesticide residues from the diet,” the French researchers said.
A team from Harvard TH Chan Folkhälsohögskolan noted several strengths in the new report in a comment that was also published on Monday.
Glyphosate, malathion and diazinone have all been associated with non-Hodgkin’s lymphoma, so researchers can be on something the Harvard authors wrote. They also commended the study to include tens of thousands of people and follow them prospectively rather than retrospectively.
But there are also several shortcomings that limit the strength of the study results, they allow.
For example, no attempt was made to confirm people’s claims about how much organic food they ate. The French researchers also assumed that the more organic food one person ate, the lower their exposure to pesticide residues would be. It may be true, but there is no data to back up it.
“At the current research stage, the relationship between organic food consumption and cancer risk is still unclear,” wrote Harvard researchers.
What is “urgent” needed is a more detailed study that would address some of the problems in the French report, according to the comment.
“If future studies provide more solid evidence that supports the consumption of organic foods for cancer prevention, measures to reduce costs and ensure fair access to organic products will be crucial,” Harvard authors said.
In the meantime, “concerns about pesticides do not deter the intake of conventional fruits and vegetables,” they advised. “The benefits of consuming conventionally grown products are likely to outweigh the potential risks of exposure to pesticides.”
Healthy diets linked to better results in colorectal cancer
Association of Frequency of Organic Food Consumption with Cancer Risk, JAMA Intern Med . Published online on October 22, 2018. DOI: 10.1001 / jamainternmed.2018.4357, https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2707948