Many people opt for organic foods, especially fruits and vegetables, because these foods contain little or no synthetic pesticide residues-and thus, they hope, such foods will reduce the risk of cancer and other ailments compared to their conventional counterparts. In October 2018, a large observational French study, published online in JAMA Internal Medicine, lent support to their beliefs, though there are important caveats.
The study involved 69,000 people (78 percent women, average age 44) who filled out detailed food questionnaires. Over the next 40 years, those with the highest intake of organic foods reported 25 percent fewer cases of cancer overall than those with the lowest intake. The absolute risk reduction was about 6 fewer cases of cancer per 1,000 people. But among specific cancers, only lymphoma and postmenopausal breast cancer were reduced.
The volunteers in the study were more health-conscious and better educated, on average, than the general French population. And, as expected, those who reported the highest intake of organic foods tended to have better health habits-such as healthier overall diets, less smoking, and lower body weight-than those not consuming organic foods, as well as higher income and education levels. The researchers controlled for such factors but could not rule out “residual confounding resulting from unmeasured factors”-that is, there may be other things about high organic consumers that reduce their cancer risk.
There have been few large studies on organic foods and cancer risk. In 2014, the Million Women Study in the U.K. found no association between organic consumption and overall cancer rate, and actually found a small increase in breast cancer in women who usually or always ate organic food.
As the editorial accompanying the new French study stated, the relationship between organic foods and cancer risk is still unclear. The authors pointed out the limitations of the study, such as self-reported food intake, the difficulty of assessing organic food consumption in particular, and the likelihood of residual confounding. “Concerns over pesticide risks should not discourage intake of conventional fruits and vegetables, especially because organic produce is often expensive and inaccessible to many populations,” they concluded. “Current recommendations should continue to focus on modifiable risk factors that are backed by solid evidence and encourage healthy dietary patterns, including higher intake of fruits and vegetables, whether conventional or organic.”