Given that apples are one of the most widely consumed fruits in the world, [researchers Tara Louise] Walker, [Gerd] Kempermann and colleagues were interested to find out whether this fruit contains substances that might sustain or promote adult hippocampal neurogenesis. They first looked at quercetin, the most abundant flavonoid in apple peel, and then broadened the investigation to identify other pro-neurogenic factors in apples.
The results of their studies confirmed that high concentrations of phytonutrients from apples stimulated the generation of new neurons. Experiments showed that laboratory-grown stem cells from adult mouse brains generated more neurons and were protected from cell death when the phytonutrients quercetin or another compound, dihydroxybenzoic acid (DHBA), were added to the cultures.
Subsequent tests in mice showed that in distinct structures of the adult brain associated with learning and memory, stem cells multiplied and generated more neurons when the mice were given high doses of quercetin or DHBA. The effects on neurogenesis were comparable to effects seen after physical exercise, which is a known stimulus for neurogenesis.