Milk inhibits and ascorbic acid favors ferrous bis-glycine chelate bioavailability in humans

The chemical properties of ferrous bis-glycine chelate allow for its use as a fortificant in fluid, high fat vehicles. This chemical form may also protect iron from the inhibitory or enhancing effects of the diet on iron absorption. Alternatively, iron bis-glycine chelate may be absorbed by a mechanism independent of an individual's iron stores. To test these hypotheses, the bioavailability of iron bis-glycine chelate added to water and milk was studied using a double-isotopic method in two groups of 14 women. Iron absorption from aqueous solutions of 0.27 mmol/L (15 mg/L) of elemental iron as either iron bis-glycine or ferrous ascorbate was not significantly different (34.6 and 29.9%, respectively). There were significant correlations between (log) iron absorption of iron bis-glycine with (log) serum ferritin (r = -0.60, P < 0.03) and with (log) iron absorption from ferrous ascorbate (r = 0.71, P < 0.006), suggesting that iron bis-glycine chelate bioavailability is indeed affected by iron stores. Iron absorption of iron bis-glycine given in milk was significantly lower (P < 0.002) than when given in water, with values of 11.1 and 46.3%, respectively (standardized to 40% absorption of the reference dose). With the addition of 0.57 mmol/L ascorbic acid (100 mg/L), iron absorption of iron bis-glycine given in milk increased significantly from 11.1 to 15.4% (P < 0.05). These findings show that milk and ascorbic acid affect iron bis-glycine chelate bioavailability and also demonstrate that iron stores may influence its bioavailability as well. The good bioavailability of iron bis-glycine makes this compound a suitable alternative to be considered in iron fortification programs.