Iron

For someone who has been genuinely iron-deficient, correcting the deficiency can feel like a light switch flipping on. The most commonly reported changes are a return of physical energy, resolution of brain fog, improved exercise tolerance, and the disappearance of restless leg symptoms that may have been dismissed as stress or poor sleep. Some people describe the shift as dramatic within the first few weeks of supplementation, particularly those whose ferritin levels were severely depleted. Online health communities frequently reference a ferritin threshold of around 30 ng/mL, below which many people report persistent symptoms even if their hemoglobin technically remains in the "normal" range. Getting ferritin into the 50-100+ range is often cited as the point where people feel noticeably better.

It is worth being direct about the other side of this: if you are not iron-deficient, supplementing iron will not give you more energy, sharpen your focus, or improve your workouts. Iron is not a stimulant and has no performance-enhancing effect in replete individuals. Taking unnecessary iron is not harmless either. Excess iron causes gastrointestinal distress in the short term (nausea, constipation, dark stools) and oxidative damage over the long term. The only way to know whether iron supplementation will help you is to test your levels first. A serum ferritin test is the minimum, and a full iron panel (serum iron, TIBC, transferrin saturation, ferritin) gives the complete picture.

Iron exists in two oxidation states biologically: ferrous (Fe2+) and ferric (Fe3+). In the brain, iron-dependent enzymes include: tyrosine hydroxylase (rate-limiting enzyme for dopamine/norepinephrine/epinephrine synthesis, requiring Fe2+ and tetrahydrobiopterin), tryptophan hydroxylase (rate-limiting for serotonin synthesis), monoamine oxidases (MAO-A and MAO-B, containing FAD and iron), ribonucleotide reductase (DNA synthesis), cytochrome c oxidase (Complex IV of the electron transport chain), and prolyl hydroxylases (HIF regulation).

Iron homeostasis is tightly regulated because free iron is toxic. Transferrin transports iron in blood, transferrin receptor 1 (TfR1) mediates cellular uptake, ferritin stores iron intracellularly, and ferroportin exports iron. In the brain, astrocytes and oligodendrocytes concentrate iron. Hepcidin, the master iron regulatory hormone produced by the liver, controls systemic iron through ferroportin degradation.

Iron overload generates reactive oxygen species through the Fenton reaction (Fe2+ + H2O2 -> Fe3+ + OH- + OH*), producing the highly damaging hydroxyl radical. Iron accumulation in the substantia nigra is a consistent finding in Parkinson's disease, and in Alzheimer's disease, iron co-localizes with amyloid plaques and neurofibrillary tangles.

• Main article: History of ferrous metallurgy

Development of iron metallurgy

Iron is one of the elements undoubtedly known to the ancient world. It has been worked, or wrought, for millennia. However, iron artefacts of great age are much rarer than objects made of gold or silver due to the ease with which iron corrodes. The technology developed slowly, and even after the discovery of smelting it took many centuries for iron to replace bronze as the metal of choice for tools and weapons.

Meteoritic iron

Beads made from meteoric iron in 3500BC or earlier were found in Gerzeh, Egypt by G. A. Wainwright. The beads contain 7.5% nickel, which is a signature of meteoric origin since iron found in the Earth's crust generally has only minuscule nickel impurities.

Meteoric iron was highly regarded due to its origin in the heavens and was often used to forge weapons and tools. For example, a dagger made of meteoric iron was found in the tomb of Tutankhamun, containing similar proportions of iron, cobalt, and nickel to a meteorite discovered in the area, deposited by an ancient meteor shower. Items that were likely made of iron by Egyptians date from 3000 to 2500BC.

Meteoritic iron is comparably soft and ductile and easily cold forged but may get brittle when heated because of the nickel content.

Wrought iron

• Main article: Wrought iron
• Further information: Ancient iron production

The first iron production started in the Middle Bronze Age, but it took several centuries before iron displaced bronze. Samples of smelted iron from Asmar, Mesopotamia and Tall Chagar Bazaar in northern Syria were made sometime between 3000 and 2700BC. The Hittites established an empire in north-central Anatolia around 1600BC. They appear to be the first to understand the production of iron from its ores and regard it highly in their society. The Hittites began to smelt iron between 1500 and 1200BC and the practice spread to the rest of the Near East after their empire fell in 1180BC. The subsequent period is called the Iron Age.

Artifacts of smelted iron are found in India dating from 1800 to 1200BC, and in the Levant from about 1500BC (suggesting smelting in Anatolia or the Caucasus). Alleged references (compare history of metallurgy in South Asia) to iron in the Indian Vedas have been used for claims of a very early usage of iron in India respectively to date the texts as such. The rigveda term ayas (metal) refers to copper, while iron which is called as śyāma ayas, literally "black copper", first is mentioned in the post-rigvedic Atharvaveda.

Some archaeological evidence suggests iron was smelted in Zimbabwe and southeast Africa as early as the eighth century BC. Iron working was introduced to Greece in the late 11th centuryBC, from which it spread quickly throughout Europe.

The spread of ironworking in Central and Western Europe is associated with Celtic expansion. According to Pliny the Elder, iron use was common in the Roman era. In the lands of what is now considered China, iron appears approximately 700–500BC. Iron smelting may have been introduced into China through Central Asia. The earliest evidence of the use of a blast furnace in China dates to the 1st century AD, and cupola furnaces were used as early as the Warring States period (403–221 BC). Usage of the blast and cupola furnace remained widespread during the Tang and Song dynasties.

During the Industrial Revolution in Britain, Henry Cort began refining iron from pig iron to wrought iron (or bar iron) using innovative production systems. In 1783 he patented the puddling process for refining iron ore. It was later improved by others, including Joseph Hall.

Cast iron

• Main article: Cast iron Cast iron was first produced in China during 5th century BC, but was hardly in Europe until the medieval period. The earliest cast iron artifacts were discovered by archaeologists in what is now modern Luhe County, Jiangsu in China. Cast iron was used in ancient China for warfare, agriculture, and architecture. During the medieval period, means were found in Europe of producing wrought iron from cast iron (in this context known as pig iron) using finery forges. For all these processes, charcoal was required as fuel.

Medieval blast furnaces were about 10 feet (3.0m) tall and made of fireproof brick; forced air was usually provided by hand-operated bellows. Modern blast furnaces have grown much bigger, with hearths fourteen meters in diameter that allow them to produce thousands of tons of iron each day, but essentially operate in much the same way as they did during medieval times.

In 1709, Abraham Darby I established a coke-fired blast furnace to produce cast iron, replacing charcoal, although continuing to use blast furnaces. The ensuing availability of inexpensive iron was one of the factors leading to the Industrial Revolution. Toward the end of the 18th century, cast iron began to replace wrought iron for certain purposes, because it was cheaper. Carbon content in iron was not implicated as the reason for the differences in properties of wrought iron, cast iron, and steel until the 18th century.

Since iron was becoming cheaper and more plentiful, it also became a major structural material following the building of the innovative first iron bridge in 1778. This bridge still stands today as a monument to the role iron played in the Industrial Revolution. Following this, iron was used in rails, boats, ships, aqueducts, and buildings, as well as in iron cylinders in steam engines. Railways have been central to the formation of modernity and ideas of progress and various languages refer to railways as iron road (e.g. French chemin de fer, German Eisenbahn, Turkish demiryolu, Russian железная дорога, Chinese, Japanese, and Korean 鐵道, Vietnamese đường sắt).

Steel

• Main article: Steel
• See also: Steelmaking Steel (with smaller carbon content than pig iron but more than wrought iron) was first produced in antiquity by using a bloomery. Blacksmiths in Luristan in western Persia were making good steel by 1000BC. Then improved versions, Wootz steel by India and Damascus steel were developed around 300BC and AD500 respectively. These methods were specialized, and so steel did not become a major commodity until the 1850s.

New methods of producing it by carburizing bars of iron in the cementation process were devised in the 17th century. In the Industrial Revolution, new methods of producing bar iron without charcoal were devised and these were later applied to produce steel. In the late 1850s, Henry Bessemer invented a new steelmaking process, involving blowing air through molten pig iron, to produce mild steel. This made steel much more economical, thereby leading to wrought iron no longer being produced in large quantities.

Foundations of modern chemistry

In 1774, Antoine Lavoisier used the reaction of water steam with metallic iron inside an incandescent iron tube to produce hydrogen in his experiments leading to the demonstration of the conservation of mass, which was instrumental in changing chemistry from a qualitative science to a quantitative one.