Iron deficiency (ID) can affect as many as two billion people worldwide. It is especially common in pregnant women and young children. Although ID is easily treated with Fe supplementation, excess Fe has been associated with disrupted absorption of other metals, including manganese (Mn).
Researchers investigated the effects of dietary Fe concentration on Mn bioavailability in rats fed inorganic or organic Mn sources. Results showed Mn concentrations were greater in MnLys-fed (organic) rats than in MnSO4-fed (inorganic) rats, and were also greater in low Fe rats than in adequate Fe or high Fe rats.
Manganese has already been shown to interfere with iron absorption in humans because of similar physicochemical properties and shared absorptive pathways. One study demonstrated that manganese inhibited iron absorption both in solutions and in a hamburger meal, pointing to a direct competitive inhibition of manganese on iron absorption.
This competitive inhibition was also shown in a study that stated iron status, as measured by serum ferritin concentration, was strongly associated with the amount of manganese absorbed from a meal by young women. When greater amounts of manganese are absorbed, the body may compensate by excreting manganese more quickly.
While the results from the latest study were achieved in animals, there may be implications on how and in what form Fe supplementation should be distributed in food distribution programs and fortification processes.
Non-heme iron can form an insoluble complex with several other drugs, resulting in decreased absorption of both iron and the other drug. The same can occur with elements in food, such as calcium.
Dr Huaiyong Zhang lead researchers from the Sichuan Agricultural University of China and Virginia Tech University in comparing the effects of dietary Fe concentration on Mn bioavailability in rats fed inorganic and organic Mn sources. They hypothesised that organic Mn would improve Mn bioavailability in rats.
Fifty-four male rats were randomly assigned and fed a diet supplemented with 0 (low Fe (L-Fe)), 35 (adequate Fe (A-Fe)) or 175 (high Fe (H-Fe)) mg Fe/kg. This was supplemented with an organic (MnLys) and inorganic source of manganese (MnSO4).
“Final body weight and body weight gain were higher in the MnLys-fed rats than in the MnSO4-fed rats,” the study found.
“The H-Fe diet decreased the final body weight and body weight gain as compared with the A-Fe diet. Feed intake was lower in H-Fe rats and tended to be lower in L-Fe rats than in A-Fe rats. Feed efficiency was not significantly affected by Mn source, dietary Fe level or their interaction.”
In addition, the study found serum Fe increased, whereas serum total Fe-binding capacity (TIBC) decreased with increasing dietary Fe concentration, irrespective of the Mn source. Blood Hb also rose with increasing dietary Fe concentration, although blood Hb concentration in A-Fe rats did not differ in H-Fe rats when fed the MnLys diet.
Consumption of the MnLys diet increased blood Hb concentration as compared with the MnSO4 diet for A-Fe rats. Serum Mn was higher in rats fed the MnLys diet than in those fed the MnSO4 diet. The Mn source and interaction between the Mn source and dietary Fe concentration did not influence blood Hb, serum Fe and serum TIBC concentrations in rats.
Mechanism of action
The researchers pointed to the protein DMT1 as the predominate factor involved in Fe ion uptake by the cell. In this study, the increase in intestinal DMT1 mRNA and protein expression in L-Fe rats was likely to indicate the rat’s L-Fe status and increased need for dietary Fe to meet their requirements.
The researchers also agreed with the idea that dietary Fe concentration may interfere with tissue metabolism of other trace elements including Mn.
“In this study, consumption of the L-Fe diet increased Mn status as indicated by the biomarker of Mn availability (serum Mn), as compared with the A-Fe and H-Fe diets. The decrease in serum Mn suggests that the H-Fe diet decreased intestinal Mn absorption consistent with what has been reported for pigs and calves,” the study noted.
The study concluded that H-Fe diet decreased the availability of Mn and MnLys, suggesting Mn from MnLys was at least partly absorbed through intestinal Fe transporters. However, the MnLys was more bioavailable than MnSO4 for the weaning rats, as demonstrated by the biomarker of Mn availability (serum Mn).
The result was consistent with a previous study in broiler chickens in which certain organic Mn sources showed higher Mn transport and absorption, and DMT1 may have been involved in the regulation of organic Mn transport in the proximal small intestine of broilers.
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Source: British Journal of Nutrition
Published online ahead of print, doi:10.1017/S0007114515004900
“Dietary iron concentration influences serum concentrations of manganese in rats consuming organic or inorganic sources of manganese.”
Authors: Huaiyong Zhanga, Elizabeth R. Gilberta, Shuqin Pana, Keying Zhanga, Xuemei Dinga, Jianping Wanga, Qiufeng Zenga and Shiping Baia.