Salivary Cystatin SN Binds to Phytic Acid and is a Predictor of Non-heme Iron Bioavailability With Phytic Acid Supplementation

Phytic acid is a known inhibitor of iron bioavailability, although long term studies have suggested possibly exaggerated findings compared to single meal studies, pointing to phytic acid adaptation over time. Salivary proline-rich proteins have been found to reduce tannin-iron chelation, but studies have not explored changes in salivary proteins that may result in phytic acid adaptation. The primary objectives of this study are: 1) To determine whether phytic acid impacts iron bioavailability or status when consumed over time 2) to test whether salivary protein production may impact iron bioavailability with phytic acid supplementation, and 3) to explore in vitro phytic acid salivary binding. Secondary objectives included assessment of the reliability of astringency as a measure of salivary protein production and iron absorption.

The study was conducted in an iron absorption study of 7 women, aged 18-35 years old, to determine iron bioavailability with supplementation of 350 mg phytic acid before and after regular, three times daily supplementation for four weeks. Direct iron absorption was measured using area under the curve. Iron status was measured by changes in hemoglobin and ferritin, and was adjusted by participant c-reactive protein levels. Salivary samples were collected before and after supplement consumption during meal challenges, and analyzed on HPLC and by ELISA. Astringency testing was conducted at the end of each meal challenge. In vitro saliva-phytic acid modeling was explored on HPLC, MALDI-TOF, and ELISA. Iron absorption and status markers were analyzed by ANOVA, and mixed-modeling followed by pairwise comparison by least significant differences. Pearson's correlations were used to correlated salivary proteins and astringency with iron bioavailability.

The present study will provide important information regarding the approximate influence of phytic acid consumption on iron bioavailability and storage over time in regards to salivary proteins. It will also give context to the role of salivary proteins with phytic acid consumption over time. Data will also help to delineate possible physiological mechanisms underlying phytic acid adaptation and possible ways to detect individuals who better adapt than others.