Iron: Digestion & absorption

This article is going to be the first on the topic of iron, how much we need, the roles it plays, how it’s used, digested and how our body’s maintain our iron stores, and how athletes are more prone to having lower iron stores. This will all result in a final breakdown of anemia or iron deficiency development, and it’s effects on athletic performance.

Iron is found in our diets in both plant and animal products, and it is found in it’s elemental (ferric) form. Human’s need to consume iron on a daily basis, as we can store between 1-3g in the body, in various forms, but we lose iron all the time via intestinal cell recycling (enterocytes), sweat, menstrual cycles and loss of skin cells. These losses account for approx. 1-2mg per day. Iron is used to carry oxugen around the blood and in the muscles, it is also used ot make red blood cells in bone marrow and is stored in the liver mainly as ferritin, this is your back up store, inadequate iron will result in poorer oxygen transport, saturation and breathing difficulties, it can also lead to extreme fatigue and cognitive impairment.

Although iron is found in both plant and animal products, animal sources are typically more bioavailable, as they contain heme iron (hemoglobin + myoglobin), which is absorbed better than the non-heme iron found in plant products, due in part to the high level of phytates found in plant foods, which impact on absorption. The absorption rate of heme iron is around 15-35%, whereas non-heme iron absorbs at rates of 2-20%. The varied rates of absorption are down to the bioavailability, transporter acitivity and inhibitors – Calcium, Zinc, Magnesium, Polyphenols and tannins (things that give tea & coffee colour) will all impede on iron absorption. It is recommended to get between 10-20mg per day, people following plant based diets should aim closer to 20mg, whereas standard diets can aim between 10-15mg. Unless an individual has iron deficinecy anemia, classified as low ferritin stores, haemoglobin, increased transferrin and TIBC, supplements are not recommended. Iron shouldn’t be taken in a prophylactic manner, to prevent deficiency, in certain cases, it is warranted, but this is not applicable to 99% of poeple reading this. Interestingly enough, your body actually down-regulates iron absorption rates when your stores are adequate or high, to keep it in or bring back to range.

It should be noted however, that consumption of vitamin C with iron rich foods, over rides any absorption inhibitors, as it is acidic, and helps activate the ascorbate ferrireductase transmembrane protein along cytochrome B, transforming the ferric iron into ferrous iron. Ferrous iron is then shuffled byt DMT1 into the intestinal cells (enterocyte). Heme iron has the distinct advantage of being absorbed directly by heme transporters, whereas the ferric iron must be reduced into ferrous iron first.

The vast majority of iron absorption occurs in the duodenum and the jejunum, these are both sections of the small intestine, and both are in close proximity to the stomach. This is likely due to the fact that iron requires an acidic environment (remember vitamin C a.k.a. ascorbic acid) to be better absorbed. Iron absorption is typically somewhere between 1-2mg per day, we do not absorb all of the iron from our diets, this is a good thing, as our bodies have no real excretion mechanism, it simply leaves our body when cells die, or with blood loss. Iron absorption is closely controlled by ferroportin and tranferrin, ferroportin is essentially the door that allows iron out of the intestinal cells into the blood, and transferrin is what carries it around the body to the liver, muscles or bone marrow. When iron levels get too high (there are reference ranges fro men and women), the body releases hepcidin, which blocks ferroportin, essentially trapping iron in intestinal cells, thus rendering us unable to absorb iron. Haemochromatosis is a genetic condition, where individuals have defective hepcidin, and the iron can build up to limitless levels. High levels of serum iron are neurotoxic, and cause a lot of redox and tissue damage, alongside providing a perfect growth medium for infectious bacteria.

That’s requirements and absorption in a nutshell, our bodies have an easier time absorbing heme iron sources, but it is still possible to get your needs via a plant based diet (harder to do), and there are things that will impact on our iron absorption, which is lower than you may have thought. Your body is very clever and resourceful at managing iron levels, and will exude a series of responses including changing ferroprotin, transferrin and intestinal ferric reductase activity, and hepcidin levels, in order to maintain tight control of our iron levels.*

*In a healthy person

Next up, how anemia and iron deficiency occurs, followed by a final article on anemia & athletes.

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