Iron, element number twenty-six, is a mineral nutrient that is essential for numerous functions in the human body, the most well-known in the form of hemoglobin in the red blood cells to transport oxygen and carbon dioxide around the body. The recommended daily intake of iron for adult men is 8 mg and for adult women is 18 mg. Getting enough iron is one of many keys to good health and failure to do so can lead to serious health problems, such as anemia. Iron, like most things about the human body should be kept in equilibrium for optimal health: Too much is as dangerous as too little. Iron overdose is potentially fatal.
Acute iron toxicity is reported to begin around 20 mg/kg (20 mg of elemental iron per each kg of body mass) with a fatal dose in the 60 mg/kg range. For someone my size (roughly 100 kg), this means that I will encounter acute toxicity after consuming 2000 mg of iron and will approach a fatal dose at 6000 mg. Keep in mind that the average adult human has 3000 – 4000 mg of iron in their body at any given time.
Chronic iron toxicity occurs when lower doses of iron are consumed for longer periods of time. The quantity of iron and length of time will vary from person to person. Iron overdose can easily occur where there is ready access to iron-fortified foods and iron-containing supplements and iron is one of the most added nutrients to basic foods (e.g. cereals, breads, flour). If you are reading the ingredient list and see 'reduced iron' that is added iron. Reduced refers to the chemical process of reduction which is the opposite of oxidation. Reduced iron is, literally, iron metal. Mineral supplements often contain an iron salt (e.g. iron gluconate, iron sulfate) that is easier for the body to absorb. Cereals often contain reduced iron as it is less expensive. Many people who take chemistry in college will perform the experiment where a fortified breakfast cereal is stirred in water and the iron filings are collected and weighed. I did this very experiment as a freshman.
After it reaches the stomach, reduced iron is converted into iron chloride by the hydrochloric acid present where it can then be absorbed. Some breakfast cereals contain high levels of iron, arbitrarily defined as 100% of the suggested daily intake value, typically 18 mg. Eating one serving of these cereals isn't any cause for concern, even if eaten daily. Eating more than a serving at a time, every day, for extended periods of time can cause some adverse effects. If the cereal contains 100% DV (daily value) of iron and you eat two servings every day, you are getting twice as much as you need (if female, and 4.5X if male) just at breakfast and you will likely encounter more iron at lunch and dinner (e.g. from meat, leafy green veggies, nuts, legumes). You could easily be eating two to five times as much iron as you need every day. But, you say, toxicity starts at 20 mg/kg and even if you weigh 50 kg so you are quite far from a toxic dose. That’s true. You would be quite far from an acutely toxic dose but not necessarily a harmful chronic dose.
So, what does this mean for those of us who regularly eat iron-fortified breakfast cereals? It simply means not eating a highly-fortified cereal regularly. There are other cereals you can eat and other breakfast choices that are just as easy as cereal (e.g. bagel with spread).
What I can say about my own experience with iron, and nutrition in general, is that we must always keep an eye on what we eat and to become wary if we find ourselves eating the same thing over and over again. While this isn’t always a cause for concern, a brief survey of what we are putting into our bodies can prevent negative effects both short- and long term. If you always have a slice of cheese pizza for lunch, you may want to look up the nutritional data on the specific brand you are eating or, if you don’t know the brand, just looking up some general information on the nutritional content of pizza in general will help inform your decision to continue eating it or not. People on sodium-restricted diets must do this all the time, as must diabetics and those with gastro-intestinal conditions like Crohns’ or IBS. Even something as relatively mild as lactose intolerance is a cause for evaluating what you are eating.
Based on my daily diet, I estimated that I was getting about 700% of my daily value for iron at breakfast, a full order of magnitude below the acutely toxic threshold. I was feeling slightly ill all the time with a distinct odor on my breath and regular acid breakthrough from acid reflux as well as intestinal disturbances. I was also experiencing regular fatigue and some cloudiness of thought and I was having trouble falling asleep and staying asleep. Within forty-eight hours of reducing my iron intake, all of the above symptoms were noticeably less severe. After one week, I continued to feel better with little acid breakthrough, improved sleep, and greatly reduced fatigue. I could also eat spicier foods without getting upset stomach.
The conclusion of my inadvertent experiment is that we must always be aware of what we are doing to ourselves. We want to be healthy and try to do the right thing but sometimes we sabotage ourselves, as I did, even inadvertently. As with all things we take into our bodies, the only difference between a medicine and a poison is the dose. Iron, vitamins, even water are dangerous in the right dose. Stay vigilant and stay healthy.