The Iron in Your Blood Came From the Stars: Surah Al-Hadid 57:25

Every breath you take depends on iron. Each red blood cell carries hemoglobin, and at the heart of every hemoglobin molecule sits an iron atom that holds oxygen in the lungs and releases it in your tissues. But where did that iron come from? Modern astronomy gives a surprising answer: not from the Earth. It was made inside stars that died long before our Sun was born.

From stars to blood: the journey of iron

About 13.8 billion years ago the universe began with almost nothing but hydrogen and helium. Heavier elements had to be built. Inside giant stars, more than about eight times the mass of our Sun, nuclear fusion builds heavier elements layer by layer: helium, carbon, oxygen, silicon and finally iron. The innermost stage, at roughly three billion degrees, ends in an iron core, first made as nickel-56, which then decays into iron.

Iron is the end point. Fusing iron does not release energy, so the star's core can no longer hold itself up. It collapses, and the star explodes as a supernova, scattering iron and other elements into space. About 4.6 billion years ago, our Sun and Earth formed from a cloud of gas and dust enriched by such explosions. Today about a third of Earth's mass is iron. From the rocks it reaches the soil, from the soil plants, from plants our food, and finally the hemoglobin in our blood.

• An adult has roughly 25 trillion red blood cells.
• Each red cell holds about 270 million hemoglobin molecules.
• Each hemoglobin molecule contains four iron atoms, and each iron atom can carry one oxygen molecule.
• Most of the iron in your body sits in hemoglobin.

What Surah Al-Hadid says

The 57th surah of the Quran is named Al-Hadid, 'Iron'. In verse 25 Allah says that He sent down the Book and the Balance with the messengers, and then: 'And We sent down iron, in which is great might and benefits for people.' The verb used is anzalnā, 'We sent down'.

Many people today reflect on this word: astronomy tells us that iron was not formed on Earth but reached it from space, from the remains of stars. The verse also names two sides of iron that everyone can see: great might (ba'sun shadīd), the strength used in tools and weapons, and benefits for people (manāfi'), from construction to the very blood in our veins.

An honest note on the word 'sent down'

Classical scholars of tafsir also explain anzalnā here as 'bestowed' or 'provided', because the Quran uses the same verb for cattle (39:6) and for clothing (7:26), which were not literally dropped from the sky. So the link with astronomy is a reflection on the wording, a tadabbur, not a claim that the verse is a science textbook. We believe this honesty makes the reflection stronger, not weaker: the verse is true in its classical meaning, and modern discoveries give us one more reason to stop and think.

Video question: what is it called when the body is low on iron?

It is called iron-deficiency anemia. With too little iron the body cannot make enough hemoglobin, so less oxygen reaches the organs. Common signs include tiredness, dizziness, shortness of breath and pale skin. If you notice these signs, see a doctor for a proper diagnosis; do not start iron supplements without medical advice.

Key takeaways

• Iron is forged in giant stars and spread by supernova explosions.
• Earth is about one third iron, and that iron reaches our blood through soil and food.
• Surah Al-Hadid 57:25 says iron was 'sent down' and holds great might and benefits for people.
• The astronomy link is a reflection on the wording; classical scholars also read the verb as 'bestowed'.