title: Greeen tea extracts lower serum folates in rats at very high dietary concentrations only and do not affect plasma folates in a human pilot study.
abstract: Green tea catechins (GTC) have been shown to inhibit the activities of enzymes involved in folate uptake. Hence, regular green tea drinkers may be at risk of impaired folate status. The present experiments aimed at studying the impact of dietary GTC on folate concentrations and metabolism. In a human pilot study (parallel design) healthy men consumed for 3 weeks 6 capsules (approximately 670 mg GTC) per day (2 capsules with each principal meal) containing aqueous extracts of the leaves of Camellia sinensis (n=17) or placebo (n=16). No differences in plasma folate concentrations were observed between treatments. We further fed groups of 10 male rats diets fortified with 0, 0.05, 0.5, 1, or 5 g GTC/kg for 6 weeks. Only at the highest intake, GTC significantly decreased serum 5-methyl-tetrahydrofolate concentrations in rats, while mRNA concentrations of reduced folate carrier, proton-coupled folate transporter/heme carrier protein 1, and dihydrofolate reductase (DHFR) remained unchanged in intestinal mucosa. Using an in vitro enzyme activity assay, we observed a time- and dose-dependent inhibition of DHFR activity by epigallocatechin gallate and a green tea extract. Our data suggest that regular green tea consumption is unlikely to impair folate status in healthy males, despite the DHFR inhibitory activity of GTC.
authors.affiliation: Institute of Human Nutrition and Food Science, Christian Albrechts University, Kiel, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Augustin
authors.forename: J
authors.initials: J
authors.lastname: Frank
authors.forename: S
authors.initials: S
authors.lastname: Augustin
authors.forename: P
authors.initials: P
authors.lastname: Langguth
authors.forename: V
authors.initials: V
authors.lastname: Ohrvik
authors.forename: C M
authors.initials: CM
authors.lastname: Witthoft
authors.forename: G
authors.initials: G
authors.lastname: Rimbach
authors.forename: S
authors.initials: S
authors.lastname: Wolffram
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D028241:Camellia sinensis / Q000737:chemistry*; D002392:Catechin / Q000008:administration & dosage / Q000009:adverse effects* / Q000302:isolation & purification / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D004032:Diet; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005492:Folic Acid / Q000008:administration & dosage / Q000096:biosynthesis / Q000097:blood*; D005493:Folic Acid Antagonists / Q000008:administration & dosage / Q000009:adverse effects* / Q000302:isolation & purification / Q000494:pharmacology; D006801:Humans; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D010936:Plant Extracts / Q000008:administration & dosage / Q000009:adverse effects* / Q000302:isolation & purification / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011795:Surveys and Questionnaires; D013762:Tetrahydrofolate Dehydrogenase / Q000096:biosynthesis; D055815:Young Adult
chemical_list: D005493:Folic Acid Antagonists; D010936:Plant Extracts; D002392:Catechin; D005492:Folic Acid; D013762:Tetrahydrofolate Dehydrogenase