A recent literature review published in the Annals of Internal Medicine concludes that organic food consumption may reduce exposure to pesticide residues and antibiotic resistant bacteria but also says that there is no strong evidence that organic food is more nutritious than conventional food. The authors extracted data on methods, outcomes, and results of 237 peer-reviewed English language studies published in the scientific literature.
The reviewers used strict criteria to determine which studies would be included in the study. Out of 5’908 potential articles screened by their abstracts, only about 4% met the criteria for inclusion. Many studies were not included because the farming practices were not fully specified, the methodology was not adequately described, or the sample sizes were not reported. For the studies that directly evaluated foods, the participants needed to provide consent, an institutional review board needed to review the study and the researchers could not receive funding from organizations with an interest in the outcomes. The articles included then had their data extracted and analyzed for homogeneity, publication bias, and statistical significance. The methodology was conservative in the level of significance and robustness of the studies to be conclusive. Data from individual studies were removed from the pooled data to determine if the conclusions were robust.
The authors found the lack of significance due to the heterogeneity of the studies, small sample sizes of many of the studies, and the lack of robustness of the conclusions of multiple studies. Many studies were found to be mildly favorable to organic, but the level of significance was not sufficient to support the conclusion. For the one mineral nutrient favorable to organic, phosphorous, the authors concluded that it was not important because phosphorous deficiencies are extremely rare. Other nutrients, for example total phenols and ω-3 fatty acids, were found to be at consistently higher levels but the results were not statistically significant employing the meta-analysis tool used.
The authors similarly discounted the statistically significant results of reduced risk of exposure to both pesticide residues and to antibiotic-resistant bacteria. The number of conventional samples testing positive for pesticide residues was significantly higher than organic, and the levels were also significantly higher in conventional. However, relatively few of the positive samples in the conventional exceeded legal tolerances.
The authors found that conventional chicken and pork have a higher risk of contamination with bacteria resistant to three or more antibiotics. The human health implications of antibiotic resistant bacteria in meat as opposed to misuse of antibiotics in humans is seen by the authors as an unresolved issue that is still a matter of scientific debate.
The authors also found it notable that the study found no significant difference in the levels of pathogenic bacteria between organic and conventional food. Some government officials and scientists have claimed that organic food is more likely to contain food borne pathogens than conventional food due to reduced use of disinfectants and the prohibition of food irradiation. However, those claims are not supported by scientific studies. The authors cautioned that this conclusion may not be robust and the finding needs to be confirmed by further study.
The authors state that the “results should be interpreted with caution because summary effect estimates were highly heterogeneous.” Many of the studies were subject to confounding effects, such as weather, soil, variety, ripeness and storage life. On the other hand, failure to report results in null findings may have biased the study to conclude that there are differences when none exist. The authors acknowledge that many of the field studies reviewed may not reflect real world conditions.
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Citation
Crystal Smith-Spangler, Margaret L. Brandeau, Grace E. Hunter, J. Clay Bavinger, Maren Pearson, Paul J. Eschbach, Vandana Sundaram, Hau Liu, Patricia Schirmer, Christopher Stave, Ingram Olkin, Dena M. Bravata. (2012) Are organic foods safer or healthier than conventional alternatives? A systematic review. Annals of Internal Medicine. 157: 348-366.
Link
Annals.org: Annals of Internal Medicine: Are organic foods safer or healthier than conventional alternatives? A systematic review. Abstract and instructions for purchase
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