Fig. 1. Timeline of human aging metabolomics population studies.

A timeline showing the sample size of aging metabolomics studies (by number of participants on a logarithmic scale) in humans is shown, including the metabolomics technology used and the sample type. When multiple technologies or sample types were used, the study is considered a “combination” study. There has been no strong trend in sample size over time; instead, the field is dominated by occasional studies with much larger sample sizes than the rest. There has been a shift toward more MS-based technologies, although NMR studies are still being conducted and published. Most studies have used blood or urine, although in the 2020s, a greater diversity of sample types (namely, CSF, saliva, and muscle) have started to be seen in the literature.