1 · The iron that carries oxygen has to stay ferrous
Red cells carry oxygen on hemoglobin, whose central iron atom has to stay ferrous to grab oxygen in the lung and let it go in the tissue.
2 · Nitrite pushes it to ferric, and it cannot hold oxygen
Nitrite is an oxidant: as it passes a red cell it oxidizes the hemoglobin iron from ferrous to ferric, and ferric iron can no longer hold oxygen.The blood is oxidized, yet the person is hypoxic. Lips turn blue not because there is less blood, but because the blood itself has changed color.
3 · Adults have a reductase that snaps it back on the spot
Red cells carry a reductase whose job is to turn ferric iron back to ferrous, and on ordinary days it keeps the whole affair almost invisible.When an adult occasionally takes in a little nitrite, this system smooths it out on the spot. A plate of leftovers is far below the acute line.
4 · Infants come in fast and go back slow; cancer is another road
Infant blood still holds a large share of fetal hemoglobin, which oxidizes more readily; the reductase has not finished growing in the first months.That is why infants should not eat long-held high-nitrate leafy purees. Methemoglobinemia is an acute reaction on the spot; nitrosamine carcinogenesis accumulates over a long time. The same substance walks two different roads.
Mechanism
Leftovers — the iron cannot hold oxygen
Nitrite pushes the oxygen-carrying iron to ferric; infants come in fast and go back slow.