Bioavailability of Green Tea and Coffee Polyphenols
Condition: Diet, Food, and Nutrition; Dietary Supplements
Study type: Interventional

Summary: 
      There is little information on the dietary intake, absorption, metabolism and bioavailability
      (degree to which a substance becomes available to the target tissues upon administration) of
      polyphenols (natural substances present in a variety of foods) in human participants.

      This study assessed the bioavailability in healthy participants of polyphenols from 2
      supplements containing green tea and green coffee extracts.

      Eleven participants were recruited and their habitual diet was assessed to estimate
      polyphenol intake. After completing a 24-hour urine collection, participants were given six
      green tea extract and three green coffee extract tablets, which they took daily for a period
      of 8 weeks. No tablets were taken during the last 4 weeks of the study. Further 24-hour
      urines were collected at 2, 4, 8 and 12 weeks.

      Participants were required to attend HNR (medical laboratory) the day after each 24hour urine
      collection. At these visits, they were asked to bring along their urine collections,
      completed documents (urine collection sheet, checklist for tablet intake/side effects) and
      any remaining supplements, which were used to assess tablet compliance.

      The investigators identified and quantified the amount of polyphenols in the supplement
      tablets as well as the amount of polyphenols and their metabolites in urine. The
      investigators then evaluated polyphenol bioavailability from the relationship between their
      dietary intake and urinary output.

      Evidence from this research could inform future intervention studies by providing data on the
      bioavailability of green tea and coffee polyphenols, and on the individual differences
      related to phenolic intake.
    


Intervention name(s): Green tea and green coffee extract tablets
Intervention type(s): Dietary Supplement
Intervention description(s): Tablets: participants were required to take 6 green tea and 3 green coffee extract tablets daily for a period of 8 weeks. No tablets were taken during the last 4 weeks of the study. Randomly chosen tablets were analysed to quantify their polyphenol content.
Urine collections: Several urine collections were required during the supplementation period in order have sufficient time points to estimate the plateau of the concentration of green tea and coffee polyphenols excreted in the urine to then be able to determine their bioavailability. There was a total of five 24-hour urine collections (at week 0 -before supplementation-, 2, 4, 8, and 12 -4 weeks after finishing the supplementation period).
Completion of study documents: Participants were provided with urine collection sheets, polyphenol questionnaires, checklists to record polyphenol tablet intake, and detailed instructions.
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: polyphenols; green tea catechins; coffee caffeoylquinic acids; metabolism; inter-individual variability; colonic microbiota