Table 2. Metabolites Quantified by DI–nESI–MS Differing in USA (positive correlation) and Japanese (negative correlation) Populations and Their Association with Covariates Gender, Age, and BMI^a.

	country		gender		BMI		age
metabolite	β	p value	β	p value	β	p value	β	p value
hydroxycinnamic acid (isomers)	0.004	5.05 × 10–1	0.048	1.22 × 10–18	–0.002	6.64 × 10–5	0.005	4.42 × 10–19
ascorbic acid	0.564	4.85 × 10–94	0.337	2.78 × 10–49	–0.007	1.17 × 10–3	0.013	1.05 × 10–9
benzoic acid	0.062	2.48 × 10–2	0.228	2.40 × 10–22	–0.020	2.94 × 10–17	0.014	4.73 × 10–11
caffeic acid	0.019	1.26 × 10–20	0.024	8.69 × 10–43	–0.002	9.36 × 10–25.	0.001	2.22 × 10–8
cholic acid	–0.026	2.91 × 10–11	0.010	2.97 × 10–3	0.0004	2.22 × 10–1	0.001	1.16 × 10–4
citric acid	0.246	4.91 × 10–29	0.521	1.17 × 10–156	–0.009	2.70 × 10–7	0.006	1.35 × 10–3
daidzein	–0.014	5.24 × 10–34	0.007	5.03 × 10–14	–0.0003	3.42 × 10–3	0.000	1.22 × 10–3
deoxycholic acid	0.007	2.97 × 10–12	0.009	6.98 × 10–30	–0.0004	4.91 × 10–6	0.000	3.51 × 10–8
fumaric acid	0.115	7.69 × 10–26	0.071	1.82 × 10–14	–0.001	5.41 × 10–1	0.004	8.98 × 10–6
genistein	–0.008	3.89 × 10–20	0.003	7.02 × 10–4	–0.0001	1.34 × 10–1	0.000	1.15 × 10–1
glutamic acid	0.014	2.36 × 10–1	0.210	5.27 × 10–95	–0.003	7.35 × 10–4	0.008	2.05 × 10–19
glycocholic acid	–0.007	8.38 × 10–12	0.010	2.88 × 10–28	–0.0003	4.41 × 10–4	0.000	4.29 × 10–1
glycodeoxycholic acid	–0.004	1.18 × 10–5	0.007	6.71 × 10–25	–0.0001	6.79 × 10–2	0.000	1.56 × 10–2
hippuric acid	0.643	1.48 × 10–84	0.306	6.08 × 10–29	–0.020	2.25 × 10–13	0.013	5.79 × 10–7
homovanillic acid	0.013	4.17 × 10–1	0.235	9.74 × 10–65	–0.014	1.54 × 10–25	0.011	2.75 × 10–17
indoxyl sulfate	0.056	8.83 × 10–5	0.173	1.26 × 10–44	–0.003	4.65 × 10–3	0.004	9.62 × 10–4
isovalerylglycine	–0.084	4.39 × 10–47	0.093	1.19 × 10–78	–0.004	8.28 × 10–14	0.002	3.10 × 10–5
2-oxoglutaric acid	–0.206	1.70 × 10–33	0.342	4.97 × 10–116	0.002	2.31 × 10–1	0.005	1.69 × 10–4
ketoleucine	0.107	1.64 × 10–15	0.122	2.20 × 10–26	–0.005	1.08 × 10–5	0.007	4.21 × 10–10
leucine	0.011	5.58 × 10–1	0.256	4.11 × 10–56	–0.007	3.45 × 10–5	0.012	6.48 × 10–17
N-acetylneuraminic acid	0.058	6.00 × 10–11	0.157	1.29 × 10–92	0.001	1.79 × 10–1	0.006	2.97 × 10–17
phenylacetylglutamine	0.186	2.82 × 10–15	0.287	9.39 × 10–46	–0.007	3.81 × 10–4	0.012	6.03 × 10–10
saccharin	0.084	6.52 × 10–4	0.086	3.37 × 10–5	0.006	3.47 × 10–3	0.001	6.55 × 10–1
succinic acid	0.155	7.44 × 10–28	0.235	2.85 × 10–82	0.001	4.09 × 10–1	0.007	2.81 × 10–10
vanillylmandelic acid	0.180	2.83 × 10–57	0.175	7.92 × 10–74	–0.008	1.53 × 10–15	0.008	3.86 × 10–20
p-cresol sulfate	0.737	6.48 × 10–55	0.560	7.73 × 10–45	–0.020	3.18 × 10–7	0.015	3.07 × 10–5
phenylalanine	0.011	1.48 × 10–4	0.033	1.04 × 10–41	–0.001	4.15 × 10–3	0.001	2.96 × 10–7
acetylcarnitine	0.004	6.89 × 10–1	0.003	7.02 × 10–1	0.001	4.93 × 10–1	–0.001	1.47 × 10–1
carnitine	–0.008	6.01 × 10–1	0.019	1.55 × 10–1	0.002	9.40 × 10–2	0.001	6.00 × 10–1
cotinine	–0.016	6.94 × 10–7	–0.017	8.52 × 10–10	–0.001	1.57 × 10–7	0.000	7.08 × 10–1
creatine	–0.126	7.74 × 10–9	0.498	1.36 × 10–145	–0.006	6.33 × 10–4	0.012	1.77 × 10–12
creatinine	–0.142	2.15 × 10–40	–0.156	2.63 × 10–65	0.008	6.29 × 10–19	–0.008	5.47 × 10–24
kynurenine	0.073	7.82 × 10–7	0.122	7.58 × 10–22	–0.003	6.69 × 10–3	0.007	2.19 × 10–10
nicotine	0.021	2.31 × 10–3	–0.008	1.89 × 10–1	–0.001	2.15 × 10–1	0.001	3.92 × 10–2
nicotinic acid	–0.239	3.79 × 10–47	0.092	4.08 × 10–11	–0.003	4.97 × 10–2	0.000	7.96 × 10–1
phenylacetic acid	–0.002	3.03 × 10–1	0.006	3.52 × 10–6	0.000	4.00 × 10–2	0.000	8.74 × 10–2
phenylethylamine	0.125	8.68 × 10–9	0.110	2.31 × 10–9	–0.008	4.85 × 10–6	0.009	4.87 × 10–7
proline betaine	0.201	7.99 × 10–9	0.148	5.12 × 10–7	–0.014	1.95 × 10–6	0.015	1.16 × 10–7
tyramine	–0.035	1.22 × 10–1	0.129	1.15 × 10–11	–0.008	4.41 × 10–5	0.007	1.06 × 10–4

^aCorrelation coefficients (β) and p values are listed for all metabolites. The correlation of metabolites with each variable is calculated by linear regression with other variables fixed.