Iron is an essential micronutrient. It is an essential component of hemogloben, the protein which transports oxygen around the body, and iron is also essential for regulation of cell growth and differentiation.
The two forms of naturally-occuring dietary iron are heme and nonheme. Heme iron is derived from hemogloben, and so it is found in animal foods that originally contained hemogloben. Nonheme iron is found in both plant and animal sources and it is not as easily absorbed.  However, the competition between heme and nonheme iron absorption is not well understood. It is not necessary to consume both heme and nonheme iron, as vegetarians are able to survive on just non-heme iron.
Supplements are mostly non-heme iron unless otherwise stated. Ferrous sulfate is a popular active ingredient for iron supplements, but there are others and different compounds vary in abosorption rate.
Daily Dietary RecommendationEdit
|Age (years)||Males (mg/day)||Females (mg/day)|
Anaemia, the condition where the blood is unable to carry sufficient oxygen due to insufficient hemoglobin (an iron-dependent protein) or red blood cells, is most commonly caused by a deficiency of iron and it is the first symptom one deficient in iron would notice. Rob experienced anaemia when he first tried Soylent because he forgot iron, but he was able to recognize it and compensated by adding iron to his recipe. The main symptoms of anaemia are tiredness and lack of energy. Other common symptoms are shortness of breath and changes in your appearance such as pale skin and dry nails. It is treated by increasing your intake of iron. 
Overdose in iron begins at around 10mg/kg body weight, much higher than the recommended daily dose. It is characterized by various gastrointestinal symptoms including severe vomiting, diarrhea, abdominal pain, and dehydration and lethargy. If you think you are experiencing an overdose of iron (iron poisoning), consult a doctor. 
There is some debate on whether Calcium inhibits Iron absorption, with academic papers showing both that consuming calcium and iron at the same time does and does not decrease iron absorption. Most of these studies focus on normal meals which have many other aspects of them that could affect iron absorption. One study indicated that calcium carbonate supplements do not inhibit Iron intake in the form ferrous sulfate, but calcium citrate and calcium phosphate reduced Iron intake by half. 
- ↑ 1.0 1.1 NIH Iron Factsheet
- ↑ Pubmed Abstract
- ↑ UK NIH Iron Deficiency Anaemia Guide
- ↑ Iron Poisoning on Web MD
- ↑ The inhibitory effect of dietary calcium on iron bioavailability: a cause for concern?
- ↑ Effect of calcium intake on nonheme-iron absorption from a complete diet
- ↑ Calcium supplementation: effect on iron absorption