TL;DR - to live long and healthfully with greatly reduced risks of cancer, heart disease, diabetes, Alzheimer's, Parkinson's, etc., donate blood at least semiannually.
Five minutes more:
Why Iron Is the Most Underrated Factor in HealthI read Mangan's book,
Dumping Iron: How to Ditch This Secret Killer and Reclaim Your Health. It was well worth the $7 and and 60 minutes. Mangan makes his points succinctly and doesn't repeat himself to stretch the book. And the 147 scholarly references that occupy the last fifth of the book show that Mangan did his homework.
Mangan suggests that optimal ferritin levels are 20-40 for women and 50-70 for men. That recommendation comes from Dr. William R. Ware in this paper:
The Risk of Too Much Iron: Normal Serum Ferritin Levels May Represent Signicant Health Issues. After reviewing the evidence for iron's harm, and in the absence of controlled long-term studies to determine optimal levels, Ware takes an educated guess based on this principle:
Overall, the answer to this question appears to be lower the better, provided anaemia is not the result.
This is logical, and in the absence of solid countervailing evidence, I'm going to target those levels. Of course, if hemoglobin / hematocrit lab tests show anemia, I'll boost iron incrementally until the anemia resolves.
My advice to my sons:
1. Give blood at least twice annually.
2. Know your ferritin levels - if your doctor is ordering blood work, try to get him/her to add a ferritin check.
3. Avoid / minimize consumption of iron-supplemented foods. Because U.S. Federal law requires iron to be added to flour, corn meal, and rice, grains are not your friend. (Note that Denmark and Sweden prohibit iron supplementation and will not allow importation of iron-fortified breakfast cereals because of the health risks.)
4. Consume coffee or tea with meals as they impede iron absorption.
I think giving blood regularly is by far the most important step you can take. And since the donation center will check your hemoglobin and/or hematocrit levels before accepting your donation, you are not likely to become anemic as a result.
To put this in personal perspective, the only ferritin test I have had, in 2013, was 186. Because it was in the middle of the lab reference range, I thought it was fine - oops. I donated blood in December and am scheduled to donate again next month.