Submitted to: British Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/1998
Publication Date: N/A
Interpretive Summary: It is important to understand the mechanisms that regulate absorption of iron from the intestinal tract because failure to absorb adequate amounts of iron may cause anemia, a common disorder in some groups of women and children. The occurrence of this disorder can be reduced by consuming iron supplements, but it is believed that frequent iron doses decrease the efficiency of iron absorption because the cells lining the intestine become loaded with iron from the previous supplemental dose. As a result, the iron-loaded cells apparently "block" the absorption of iron. In the present study, rats were used as models to evaluate the extent to which daily iron supplements may block iron absorption from a subsequent dose. Anemic rats were provided iron supplements either orally or by injection. Both forms of supplemental iron improved the iron status of the rats; however, absorption of iron from a test dose was higher in rats provided iron injections than in those provided oral supplements even though body iron stores were similar in both groups. These results show that there was some "blockage" of iron absorption in response to oral iron supplements but the degree of blockage was not clearly related to the amount of storage iron in the cells. Increased understanding of the factors that regulate absorption of dietary iron may lead to improved methods to prevent or reduce the occurrence iron deficiency, a nutritional disorder that is common among some groups of people.
Technical Abstract: To evaluate the extent to which oral iron (Fe) supplements may block Fe absorption from an ensuing dose, we compared the effects of oral and intraperitoneal (i.p.) Fe supplementation on Fe status in anemic rats. A ligated duodenal loop method was used to assess the effects of Fe supplements given at different rates on Fe absorption from a subsequent test dose. Rats were assigned to seven groups of eight rats each and received either oral or i.p. Fe supplements for 3 d as follows: 1) 4 mg orally daily for 3 d; 2) 4 mg orally once (1 dose on d 1, low-Fe doses on d 2 and 3); 3) 12 mg orally (1 dose on d 1, low-Fe doses on d 2 and 3); 4) 3.2 mg i.p. daily for 3 d; 5) 3.2 mg i.p. once (1 dose on d 1); 6) 9.6 mg i.p. once (1 dose on d 1); 7)low-Fe diet (control). Effectiveness of the supplements in treating Fe deficiency was assessed by determining hemoglobin Fe gain and liver Fe stores after the 3-d test period. Oral supplementation was as effective as i.p. in improving the Fe status of the rats; however, absorption of a radioiron from a test dose was higher in i.p.-supplemented rats (mean was 11.7, 17.5 and 16.7% of dose) than in orally supplemented rats (3.2, 2.5 and 1.8%) despite equal body Fe stores. Intestinal Fe absorption efficiency was similar within orally supplemented groups but those supplemented only once were more effective than or as effective as the group receiving daily supplements for three days in improving Fe status as indicated by hemoglobin regeneration efficiency. It was concluded that there was a mucosal block with the administration of oral Fe supplements but the extent of the blocking effect was not as dramatic as currently proposed.