Ginkgo biloba for preventing cognitive decline in older adults: a randomized trial. - Snitz BE; O'Meara ES; Carlson MC; Arnold AM; Ives DG; Rapp SR; Saxton J; Lopez OL; Dunn LO; Sink KM; DeKosky ST; Ginkgo Evaluation of Memory (GEM) Study Investigators; et al. (JAMA: Journal of the American Medical Association, 2009)