The jury is still out of whether organic foods are healthier than conventionally produced foods. Recent reports have concluded that organic foods have slightly higher levels of some nutrients (vitamin C, omega 3 fat) but lower levels of iodine and selenium and also lower levels of pesticide residues and cadmium.
The NutriNet_Sante study of 69,000 French adults recently reported that people who habitually consumed organic foods (all types of food including fruit and vegetables, meat, milk, cereals, vegetable oils, tea, coffee, wine) were 25% less likely to develop cancer than those who did not consume organic foods. Organic food consumers were specifically less likely to get breast cancer (after but not before the menopause) and lymphomas, but there were no differences in rates of other cancers.
This is an interesting observation which raises the possibility that organic foods may help reduce cancer risk, but is by no means definitive proof. The paper raises some key unanswered questions. Organic food consumers in the study were more healthy and less likely to smoke, and were lighter, with healthier diets. The researchers adjusted for these factors in their analysis, but there is always the possibility that these factors may still be influencing the results.
The association was strongest for lymphoma, which fits with previous research linking pesticide exposure to lymphoma. However the study only included 63 lymphoma patients. These findings would need to be replicated in a larger study.
The links with breast cancer are hard to interpret. There was no association between intake of plant derived organic foods and breast cancer, which is a specific measure of pesticide exposure. Organic foods were associated with a lower risk of developing breast cancer after rather than before the menopause, which does not make immediate biological sense. A previous report amongst 1 million women attending the UK breast screening programme associated organic food with a 9% higher chance of developing breast cancer.
They reported 36% reduction in risk of post-menopausal breast cancer risk amongst organic food consumers compares to numerous studies which show a 30% reduction in risk with being a healthy weight, physically active, limiting alcohol and not smoking. This finding has been replicated in numerous studies and is the currently the best evidence based guideline.
Further research will help us understand if organic food really can help to reduce cancer rates, and the precise mechanism, as well as which cancers may be prevented.