GDF15 and Alzheimer disease: Several novel aspects were found in the co-occurrence network, including “Alzheimer’s disease” (co-occurrence: 10 times), “hypertension” (10), “protein restriction” (11), “body composition” (12), “gdf15” (13), “chronic kidney disease” (14), and “cardiovascular disease” (15), which were all less exposed in FGF-21 research but may have potential significance (Figure 6B).