The daily iron ceiling was set by upset stomachs, not by overload
The adult upper limit came from one 97-person trial of stomach side effects, divided by an uncertainty factor of 1.5. One ordinary ferrous sulfate tablet supplies 65 milligrams.
What the study found
The 45mg daily ceiling guards against stomach upset, not overload
The adult upper limit comes from one 97-person trial of stomach side effects: a 60 milligram threshold, plus 11 milligrams of estimated food iron, divided by an uncertainty factor of 1.5. No level free of it could be identified. One ordinary ferrous sulfate tablet supplies 65 milligrams.
The caveat · Does not protect haemochromatosis
People with hereditary haemochromatosis were deliberately left out of the derivation as exceptionally sensitive, so this figure does not protect them. The same 45 milligrams was applied to pregnancy only because data on lower doses in pregnant women did not exist. The chapter was published in 2001 and has not been revised since.