American Journal of Clinical Nutrition: http://www.sciencedaily.com/releases/2009/07/090729103728.ht...
Stanford study (others referenced this): http://med.stanford.edu/news/all-news/2012/09/little-evidenc...
Those aren't conclusive and I'm open to being wrong, but this recent UK study seems to be the among the first to find significant differences. I bring up the organic definition in the US vs UK as a possible explanation for the results.