Figure 1.

The plasma levels of trimethylamine‐N‐oxide (TMAO) increased in the aged group in humans. The plasma was collected from healthy individuals. The levels of plasma TMAO, carnitine, choline, betaine and butyrobetaine were quantified using stable isotope dilution liquid chromatography–tandem mass spectrometry (LC/MS/MS). The levels of plasma choline (a), carnitine (b), betaine (c) and butyrobetaine (d) were unchanged. (e) However, the level of plasma TMAO was significantly higher in the aged group than the young‐ and middle‐aged groups, but there was no significant difference between the young‐ and middle‐aged groups in circulating level of TMAO. (f) Linear regression analysis revealed a tendency that TMAO was positively related to age in the overall studied population. (a–e) Data are shown as the mean ± SD (one‐way ANOVA followed by Tukey's multiple comparison test). Y = young adults (n = 168), M = middle‐aged adults (n = 118), E = elderly adults (n = 141) ***p < .001