Salivary Cystatin SN Is a Factor Predicting Iron Bioavailability in Phytic Acid Rich Meals

Abstract

Abstract Objectives Phytic acid is an inhibitor of iron bioavailability, but recent research has suggested that individuals may adapt to phytic acid, and that the salivary protein, cystatin SN, may play a role. Study objectives were: 1) to assess the relationship between cystatin SN levels and iron bioavailability during a phytic acid rich meal, and 2) whether cystatin SN would differ among participants with greater vs. lower iron bioavailability overall. Methods Three groups of ten women received meals with: 1) 500 mg phytic acid powder sprinkles 2) 500 mg phytic acid capsules, or 3) no phytic acid. Meals included 18 mg iron. Pre-meal, hemoglobin, iron, ferritin, total iron binding capacity, transferrin saturation, and C - reactive protein were measured from venous blood. Iron bioavailability was measured by the mealtime percentage of maximum iron recovery (% max iron absorption); cystatin SN was measured pre-and post-meal by enzyme-linked immunosorbent assay. All participants completed 3–24 hour dietary recalls. Data were analyzed by multifactor regression analysis and ANOVA. Results There were no significant differences in group dietary intake (P > 0.05). The % max iron absorption was not different among groups; after adjustment, there was significantly greater % max iron absorption in Groups 2 and 3, compared to 1 (P = 0.03, P = 0.004, respectively). Unadjusted pre-to-post meal cystatin SN levels were significantly and positively correlated with improved iron bioavailability in Group 1 (P = 0.046, R2 = 0.4), but not Groups 2 or 3. After adjusted modeling, pre-to-post meal cystatin SN was significantly associated with improved % max iron absorption in Groups 1 and 2 (P's < 0.0001). Overall, there were significantly greater pre-to-post meal cystatin SN levels in participants with % max iron absorption greater, compared to less than 12% (10.2 ± 20.6 vs. −20.5 ± 13.5, respectively, P = 0.01). Conclusions There was a significant relationship between improved iron bioavailability and pre-to-post meal Cystatin SN levels with phytic acid rich meals. Overall, participants with greater meal iron bioavailability had significantly greater pre-to-post meal cystatin SN recovery. Cystatin SN may be a physiological factor in predicting iron bioavailability with phytic acid rich meals. Funding Sources Funded by Wichita State University's School of Nursing.