Preventive Medicine: Does eating organic prevent cancer?

Dr. David Katz

Dr. David Katz

For years I have been writing — most recently in a dedicated entry in The Truth about Food — that despite my general enthusiasm for organic food, and the environmental benefits of organic farming, direct evidence of human health benefit from organic food is very scarce and quite elusive. That’s all still true this week, but with a noteworthy addendum. A study just published in JAMA Internal Medicine associates routine consumption of organic food with reduced cancer risk.

The researchers from France followed nearly 70,000 people for 10 years, lending the study great statistical power. They assessed the frequency of intake of diverse foods available in organic and conventional versions, creating a 32-point scale. They found significantly lower rates of cancer overall — a relative reduction of 25 percent on average — among those with the highest as compared to those with the lowest frequency of organic food intake.

This new study, however, was not a randomized trial. Rather, it is an observational cohort study called NutriNet-Santé. The study participants share information online about a wide range of habits and lifestyle practices, and health outcomes. The researchers analyze the associations.

Studies of association cannot prove cause and effect for a reason as obvious as schoolyard repartee: two things may be “true, true, but unrelated.” Those who eat organic food consciously and most often may simply differ systematically from those more cavalier about it. Perhaps they are more cautious about everything, more devoted to health, more mindful.

The researchers of NutriNet-Santé did an excellent job of capturing many other variables that might “explain away” the association between organic food and cancer risk. They gathered data about dietary pattern and quality, tobacco use, exercise, environmental exposures, education, and more. But this diligent effort cannot fully eliminate the possibility that eating organic and less cancer are nonetheless “true, true, and unrelated,” a concession the researchers make clearly and humbly.

Of course, a study on a topic of such wide interest engendered extensive media reactions, inevitably hyperbolic in both directions. Some headlines made the leap to cause-and-effect, offering organic food as an established opportunity to cut cancer risk. Detractors were quick to pounce and note that since the new study proved no such thing, then no such thing is true.

I don’t much care for hyperbole in either direction, but I have a particular problem with the blithe dismissal of this research in certain quarters. For one thing, let’s be clear — there are food industry interests that would simply prefer the many chemical adulterations of our food supply not be convicted of crimes they may well be committing. If denunciations of the new study spring from such sources, they cannot be trusted.

For another, as a matter of routine, research methods are criticized by entities that don’t like the findings- yet exactly the same methods are broadcast as gospel when those same entities do like the findings. All sides in the “diet wars” use this tactic, and I renounce it in every case. The strengths and limitations of given methods are what they are, independent of the findings, and independent of whether or not we happen to like them.

For yet another, there is the insinuation that because a study of mere association does not prove cause-and-effect, therefore cause-and-effect have been…disproved. This, of course, is utter nonsense. As the French authors rightly report, their study suggests an association that warrants further study. But in the interim, their study suggests the association. The group eating organic more often did experience significantly less cancer. That desirable outcome is attributable to something. The failure to achieve the threshold of definitive proof is not the same as the failure to lend support. The new study lends support to the plausible and hopeful proposition that eating organic might reduce the risk of cancer over a lifetime.

No, the new study does not prove that eating organic will reduce your cancer risk. But in the context of sense as well as science, it lends support to the hope that it might. Since there are ample, other good reasons to favor organic eating, I encourage you to do so whenever you reasonably can.