No change in efficacy or tolerance over time
Heme-iron therapy can build up adequate iron storage in a natural and gentle fashion.
There is no change in tolerability or efficacy over longer time.
With non-heme supplements side-effects are usually, even after initial good tolerance, slowly accumulating until the therapy has to be discontinued.
No danger of overdosing or poisoning
Using heme iron very little is wasted. No cases ever reported of serious side effects or poisonings in Scandinavia since decades of large-scale use.
With heme iron overdosing is not an issue.