Iron at the heart of hemoglobin is what lets your blood carry oxygen around your body.

What it means

Each hemoglobin molecule holds four iron atoms, and each of those can grab one oxygen molecule in the lungs and release it in the tissues. The binding is reversible, which is the whole trick. Carbon monoxide is dangerous because it binds to the same site far more tightly and does not let go, so the blood is still full of iron and can no longer carry anything.

The claim comes from Royal Society of Chemistry.

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