There is a genetic disorder that affects one in ten people, but most people aren't aware of it. It permits the iron in your blood to become too strong and there are adverse health effects, though I don't recall what they are. Atkins may be attempting to prevent overdosing for that portion of the population who have this and aren't aware of it.

I have it, though all I ever knew was that the iron in my blood was REALLY strong. So, I only take the mature-blends of multis, because they have lowered, sometimes no, amounts of iron.