Table 4.

Biomarkers of tea intake discovered in observational studies

Type of beverage	No. subjects	Sample type	Analytical method	Enzymatic hydrolysis	Discriminating metabolites/candidate biomarkers (HMDB ID if available)	Association with	Reference
Black tea	232	Urine (24 h)	GC-MS	Yes	4-O-Methylgallic acid (HMDB0013198)	24-HDR	[132]
Black tea	53	Urine (24 h and spot)	LC-MS	Yes	Gallic acid (HMDB0005807), 4-O-methylgallic acid (HMDB0013198)	2-Day dietary record	[33]
Green tea	968	Urine	LC-MS	Yes	Epicatechin (HMDB0001871), (−)-epigallocatechin (HMDB0038361), 4’-O-methylepigallocatechin (not in HMDB), 5-(3′,4′,5′-trihydroxyphenyl)-γ-valerolactone (HMDB0041691), 5-(3′,4′-dihydroxyphenyl)-γ-valerolactone (HMDB0029185)	FFQ	[71]
Green tea, black tea	119	Urine (24 h)	LC-MS	Yes	Kaempferol (HMDB0005801)	FFQ, 4-day food diary	[75]
Green tea	660	Urine (spot, non-fasting)	HPLC	Yes	Epicatechin (HMDB0001871), (−)-epigallocatechin (HMDB0038361), 4’-O-methylepigallocatechin (not in HMDB), 5-(3′,4′,5′-trihydroxyphenyl)-γ-valerolactone (HMDB0041691), 5-(3′,4′-dihydroxyphenyl)-γ-valerolactone (HMDB0029185)	FFQ	[72]
Tea	191	Urine (24 h, overnight)	LC-MS	Yes	Kaempferol (HMDB0005801)	FFQ	[133]
Tea	476	Urine (24 h)	LC-MS	No	Methyl(epi)catechin sulfate (not in HMDB), hydroxyphenylvaleric acid glucuronide (not in HMDB), dihydroxyphenyl-γ-valerolactone glucuronide and sulfate (HMDB0041693, HMDB0029191), 4-O-methylgallic acid (HMDB0013198), methylgallic acid sulfate(HMDB0060005), pyrogallol sulfate (HMDB0060016)	24-HDR	[37]