Long-Term Dose-Response Condensed Tannin Supplementation Does Not Affect Iron Status or Bioavailability

Area of Science:

• Human Nutrition
• Dietary Bioavailability
• Mineral Metabolism

Background:

• Phytic acid adaptation is known, but tannin effects on iron absorption are unclear.
• Salivary proline-rich proteins (PRPs) may mitigate tannin inhibition of iron absorption.
• Long-term tannin effects on iron status and bioavailability require investigation.

Purpose of the Study:

• To determine the long-term, dose-response effects of condensed tannins on iron bioavailability and status.
• To assess the role of salivary proteins in modulating iron bioavailability during tannin consumption.
• To evaluate astringency as a marker for tannin adaptation and iron absorption.

Main Methods:

• Double-blind, 3-dose crossover trial with 11 nonanemic women.
• 4-week daily condensed tannin supplementation (0.03-1.5 g) with meal challenges.
• Assessment of iron bioavailability, iron status, salivary PRP changes, and astringency.

Main Results:

• Condensed tannin supplementation did not alter iron bioavailability or status (hemoglobin, ferritin).
• Significant correlations found between tannin intake, iron bioavailability, basic PRPs (bPRPs), and cystatin production.
• Astringency ratings showed no significant change, but negatively correlated with bPRPs and cystatins.

Conclusions:

• Condensed tannin consumption does not affect iron bioavailability or status in premenopausal women.
• bPRPs and cystatins are associated with improved iron bioavailability.
• Lower astringency perception may predict better iron absorption adaptation to tannins.