A word on iron


The most abundant metal in the body and an essential component of red blood cells, iron is primarily responsible for oxygen binding/transport and electron transport.  It’s important.  But too much of a good thing can have devastating effects and, iron, unlike other nutrients, can’t always be denied entry into the body or be ushered unceremoniously out the door when too much of its ilk has overstayed their welcome.  So, how much is too little or too much?  What can happen?  How do we make sure we meet our requirements without going overboard?

First, it is important to understand how and why our bodies manage dietary iron as they do.  At a time when Homo sapiens were at a significantly higher risk of losing their contents, in no small part due to being mauled by cave lions and the occasional prehistoric hyena, or by simply stepping off a cliff while trying to escape neighbouring tribes, we developed an iron storage mechanism to ensure rapid recovery should sudden loss of blood take place.  And it was great.  Particularly since the human body can synthesize blood cells by more than 20 times the rate at which it can incorporate dietary iron.  In the absence of existing iron stores, scarfing down copious amounts of red meat in such instances would have resulted in a well fed corpse and not much else.

The ability to store iron, however, came at a cost.  As the risk of sudden blood loss decreased with time, our bodies retained the pesky habit of storing excess iron with no mechanism in place to get rid of it should it exceed our needs.  Today, iron stores are obsolete, thanks to blood banks and modern medical interventions should accidents occur, but the liability of iron stores indefinitely hanging around remains.

SO, WHAT CAN HAPPEN?

In the healthy, young body, not a whole lot, and this is true for a number of other excesses such as the occasional alcohol overload after a night out on the town.  A healthy body in its prime disposes of over-consumed substances by excreting or incorporating them for later use.  Iron can’t be disposed of once absorbed, so, it gets packed away in bio-storage “bins” throughout the body, which would be great, except we don’t stay young and in perfect health all of our lives.  We age, and as our years grow in number, so do our iron stores, unless we start paying more attention to our dietary choices early on.

The average 70 kg adult man has approximately 2,800 mg of iron in his body.  Contrast this to the amount of dietary iron intake recommended for the same:  about 8 mg per day.  Compared to the amount of iron our bodies recycle on a daily basis, the amount we need to eat seems minuscule, and, as such, harmless should we overindulge a little bit.  But is it harmless?  Not exactly.  One or more extra mg per day, every day, month, year, and decade build up to become a risk factor for heart disease and colon cancer.

While a risk factor is just that, and not necessarily an assurance that disease will develop, it is, none the less, wise to make an effort and eliminate as many risk factors as we can, within reason.  To do so, we must understand which type of iron is most likely to be of benefit and why, and we need to identify a number of sources from where to get it.

TYPES OF IRON

There are two types of dietary iron. Haem iron is found in hemoglobin (the protein in red blood cells responsible for carrying oxygen) in most animal based foods.  It can not be regulated by humans, thus, regardless of actual need, approximately 20% to 30% of haem iron present in food is absorbed.  The rest ends up in our lower intestine stirring up trouble. Needless to say, you want to consume very little, if any, of this type of iron, particularly if you are male or post-menopausal.

Non-haem iron is found in plant foods, eggs, insects and any other animals who do not carry hemoglobin (i.e. red blood).  Uptake, transport, and storage is tightly regulated to prevent both iron deficiency and toxicity.  Absorption rates increase up to ten fold when iron stores are depleted.  This is the good stuff!

ROLE IN DISEASE

In men and in postmenopausal women the iron stores increase almost linearly with age, generating an additional risk for oxidative stress-related diseases like arteriosclerosis, chronic inflammatory diseases or cancer.

Cancer – regular consumption of heme-iron has been shown to increase the production of N-nitroso compounds (NOC’s) in the colon – NOC’s are carcinogenic and are usually involved in gastro-intestinal cancers.

Diabetes – low iron stores, such as those found among vegetarian populations, are inversely related to insulin sensitivity (low iron stores = high insulin sensitivity = lowered risk for diabetes). Conversely, the more stored iron a person has, the more insulin resistant s/he is, thus, increasing risk of developing diabetes.

DEFICIENCY, ANEMIAS

Iron deficiency takes months to years to develop depending on dietary intake, gender, and age. Symptoms include: chronic fatigue, weakness, dizziness, headaches, difficulty thinking. Incidentally, some symptoms of iron overload overlap, so, it is best to leave the diagnosis to your family physician.

As iron is slowly depleted from stores, iron in hemoglobin remains normal. It is only once hemoglobin levels start to become affected that a deficiency is declared and when the body can no longer meet daily functional needs dependent on iron, the diagnosis becomes iron deficiency anemia. Low iron stores, however, do not necessarily lead to anemia.  This explains the lack of difference in anemia rates between vegetarian and non-vegetarian populations (vegetarians and vegans usually have lower iron stores than the rest of the population). In fact, there is no conclusive evidence that an absence of iron stores has any negative consequences in otherwise healthy individuals.  It is only when we are in negative balance that unpleasant things begin to happen.  Should this occur, it is better to reach for a good quality iron supplement and include more leafy greens in your diet until the problem is corrected, rather than make a run for the local steak house.

RISK FACTORS FOR ANEMIA

Obesity – hepcidin, a peptide produced by the liver and adipose tissue is a key regulator of iron homeostasis. Obesity increases hepcidin expression which, in turn, increases iron deficiency risk by decreasing iron absorption and increasing chronic inflammation in the body.

Vitamin A deficiency – can also lead to anemia. Vitamin A plays a role in releasing iron from ferritin stores for use by the body. Approximately 50 carotenoids (i.e. alpha-, beta-, and gamma-carotene) are converted by the body into vitamin A. Sources include: eggs, fortified cereals, dark orange or green vegetables.

Diet – very low intake or lack of dietary sources of iron may eventually result in a negative balance of iron in the body, primarily in premenopausal women.

Menstruation – premenopausal women require higher intakes of iron to counteract monthly losses.

HOW MUCH DO YOU NEED?

  • Adult men: 8 mg
  • Pre-menopausal women: 18 mg
  • Post-menopausal: 8 mg
  • Pregnant women: 27 mg
  • Athletes: depends on level of activity

SOURCES OF NON-HEME IRON

In plants, leaves are the major site for iron accumulation. The amount of iron in leaves increases with leaf development, with mature leaves containing the highest amounts. The exception is legumes – iron is found in higher concentrations in the beans themselves.

Dietary iron in plant foods varies depending on crop growing conditions, the specific food type, and the part of the plant consumed. In soybeans, for example, much of the ferritin is found in the hulls. Thus, foods made from whole soy such as soymilk or soy nuts contain more ferritin than foods from dehulled soy beans or processed foods such as tofu.

The best vegetarian sources of iron include:

  • Legumes (lima, soy, peas, kidney beans)
  • Dried fruits (prunes, raisins, apricots)
  • Iron-fortified cereals (depending on type of iron used for fortification)
  • Whole grains (wheat, millet, oats, brown rice)
  • Vegetables (broccoli, spinach, kale, collards, asparagus, dandelion greens)

INHIBITORS

Phytate – antioxidant found in plant foods that, when consumed in excessive amounts, interferes with iron absorption. Soaking, fermentation, germination or cooking significantly decrease this effect.

Polyphenols – found in a variety of plant foods, but only significantly inhibitory in tea (both herbal and black), beans, and chili powder. Most common are tannins.

Calcium – inhibits non-heme iron absorption, so, try to abstain from drowning your veggies in cheese.

Although phytates, polyphenols and calcium inhibit absorption in single meals, consuming a varied diet provides a fair amount of protection against these effects.

PROMOTERS

Ascorbic acid – aka vitamin C, chelates iron and reduces it from ferric to ferrous form so that it can be absorbed more easily. When consumed along with polyphenols, the inhibiting effect of these is cancelled out and vice versa. The trick is not to cook the vitamin C when using it to enhance iron absorption (i.e. use lemon juice on your spinach, after the spinach has been cooked).

Ascorbyl palimate – is a derivative of ascorbic acid that is commonly found in processed foods. It has the same beneficiary effect and is not affected by high cooking temperatures (as in baking).

FORTIFIED FOODS

The World Health Organization (WHO) recommends fortifying foods (particularly flour) with ferrous sulfate, ferrous fumarate, ferric pyrophosphate, and electrolytic iron powder. Most food manufacturers, however, use low cost elemental iron powders that are contra-indicated by WHO. Thus, unless manufacturers start to follow WHO recommendations, the fortification you see on food labels doesn’t usually amount to a hill of beans.

SUPPLEMENTS

Supplements are useful in replenishing iron stores, but should not be used indefinitely because they usually interfere with zinc absorption.

REFERENCES

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  • Theil EC, Briat JF. Plant ferritin and non-heme iron nutrition in humans. HarvestPlus Technical Monograph 1. Washington, DC and Cali: International Food Policy Research Institute and International Center for Tropical Agriculture (CIAT); 2004.
  • Tsai CJ, Leitzmann MF, Willett WC, Giovannucci EL.  Heme and non-heme iron consumption and risk of gallstone in men. Am J Clin Nutr, 2007;85(2):518-22.
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