For each 1% increase of blood ferritin, there was more than a 4% increase in heart-attack risk.
A former college running teammate of Dellinger's, Clements has theorized that ferritin, an iron complex stored mainly in the bone marrow, is used or discharged by endurance .
For each 1% increase in the amount of ferritin (a protein that binds iron), the risk of heart attack increased by 4%.