High-, but not low-bioavailability diets enable substantial control of women's iron absorption in relation to body iron stores, with minimal adaptation within several weeks

Background: Adaptation of iron absorption in response to dietary iron bioavailability is less likely in premenopausal women, who generally have lower iron stores, than in men. Objective: The objective of the study was to ascertain whether iron absorption in women adapts to dietary iron bioavailability and whether adaptation reflects altered absorptive efficiency or adjustment to specific inhibitors or enhancers of absorption. Design: Heme- and nonheme-iron absorption from either high- or low-bioavailability diets was measured at 0 and 10 wk in premenopausal women as they consumed one of the diets for 12 wk (randomized 2 X 2 factorial design). The high- and low-bioavailability diets contained similar amounts of total iron, as 13.1 and 14.8 mg/d nonheme and 2.0 and 0.3 mg/d heme iron, respectively, and they differed in contents of meat, ascorbate, whole grains, legumes, and tea. Results: In premenopausal women, the efficiency of nonheme-iron absorption (P = 0.06, two-tailed test), but not of heme-iron absorption, tended to adapt in response to a 12-wk difference in dietary iron bioavailability, whether absorption was tested with high- or low-bioavailability menus. Bioavailability, but not adaptation, substantially influenced total iron absorption (approximate to6-fold). In contrast with iron absorption from the low-bioavailability diet, that from the high-bioavailability diet consistently was inversely associated with serum ferritin. Conclusion: Only the high-bioavailability diet enabled women to absorb more iron in relation to their low iron stores. Women consuming the high-bioavailability diet absorbed up to 4.5 mg (30-35%) dietary iron with minimal influence of the diet consumed during the previous 10 wk.