Intestine, ascorbic acid-iron interaction

Mechanistic Aspects of the Ascorbic Acid—Iron Interaction in the Intestine. Studies of the mechanism of the interaction of ascorbic acid and iron at the molecular and cellular levels have yielded a variety of theories. An acidic pH in the lumen of the intestine favors the absorption... 

In the diet and at the tissue level, ascorbic acid can interact with mineral nutrients. In the intestine, ascorbic acid enhances the absorption of dietary iron and selenium reduces the absorption of copper, nickel, and manganese but apparently has little effect on zinc or cobalt. Ascorbic acid fails to affect the intestinal absorption of two toxic minerals studied, cadmium and mercury. At the tissue level, iron overload enhances the oxidative catabolism of ascorbic acid. Thus, the level of dietary vitamin C can have important nutritional consequences through a wide range of inhibitory and enhancing interactions with mineral nutrients. 

The possibility of an important interaction of ascorbic acid and iron in the human intestine was first suggested in 1940 (2). Since then, research with experimental animals and human subjects has extended and elucidated the biology of the interaction. 

The uptake of iron by the human intestine is governed not only by its dietary form and companion consituents, but also by the iron condition of the individual. Iron-depleted subjects absorb all forms of iron with greater avidity than do iron-replete individuals. In human dietetics, therefore, the ascorbic content of a diet can be included in the equation for describing the bioavailability of iron from a mixed diet (35). The interaction of iron nutrition and graded intakes of ascorbic acid (< 25 mg > 25 but < 75 mg and > 75 mg) as a prediction of iron availability from a mixed North American diet is plotted in Figure 1. 

There are numerous reports of interactions of dietary elements that cause variation in the absorption of chromium. Amino acids, which chelate chromium, prevent precipitation at the basic pH in the small intestine, which increases its absorption [13]. Other chelating agents have mixed effects. Phytates significantly decrease absorption whereas oxalates lead to increased absorption [15]. Certain vitamins such as nicotinic acid and ascorbic acid have been shown to increase absorption [16]. Starch has also been shown to increase absorption to a greater degree than glucose, fructose, and sucrose. Some metals can compete with chromium and decrease its absorption. Studies show that zinc, vanadium, and iron have a common intestinal transport mechanism with chromium and can decrease the absorption of chromium [9]. 

El-Shobaki, F. A., and Sprour, M. G., 1989, The influence of ascorbic acid and lactose on the interaction of iron with each of cobalt and zinc during intestinal absorption, Z. Erndhrungswiss. 28 310-315. 

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