IS THERE A DIFFERENCE BETWEEN ORGANICALLY AND CONVENTIONALLY GROWN PRODUCE? A SYSTEMATIC REVIEW OF THE HEALTH BENEFITS AND HARMS

Purpose: In the past decade, global sales of organic food have exploded despite 10-300% higher costs than conventional food and without detailed evidence of improved safety or nutritional content. This systematic review aims to evaluate the published evidence comparing the health benefits and harms of organic and conventional food.

Method: We considered English-language studies (indexed: 1/1966-8/2009) eligible for inclusion if they reported either a comparative evaluation of people consuming principally organic vs. conventional diets or a comparative evaluation of the food itself (we excluded processed foods). When possible, we calculated summary risk differences (RD) in pesticide or bacterial contamination and summary standardized mean differences in nutrient or contaminant levels using random effects models.

Result: We identified 5,371 citations and included 12 studies of people consuming organic vs. conventional diets and 243 studies comparing organic and conventional produce. The 12 articles of 10 human populations reported such heterogeneous outcomes (e.g., allergic outcomes in children, semen quality in adult men, serum antioxidant levels) that we could not draw conclusions about the association of organic diets with human health benefits or harms. Among the studies of produce, sample sizes were small and study methods heterogeneous. The 7 studies that examined pesticide residues in 3,029 organic and 45,184 conventional samples found that the prevalence of contamination was common in both, 3-40% for organic and 30-90% for conventional samples, but significantly lower in organic produce (RD - 0.34, p<0.0001).  Organic produce was less likely to have pesticide contamination levels above industry safety standards, although the absolute risk difference was small (RD -0.011 p=0.16).  Organic produce did not have consistently superior safety or nutritional quality in the other outcomes measured, including vitamin C content and risk of contamination with bacterial, heavy metal, or mycotoxins (p>0.05).

Conclusion: Organic produce has a significantly lower risk of contamination with pesticide residues although the absolute difference in risk of consuming produce contaminated with pesticides at levels exceeding industry safety standards was small. No other consistent differences in nutrient or contaminant content were seen. Few human dietary studies have been conducted such that no conclusions about human benefit or harm with organic produce can be reached.