A few weeks ago, I had a mystery to solve: I'd been taking iron and zinc pills, and an iron test done when I gave blood showed the highest iron reading I'd ever had. But in late August, my full blood workup showed iron deficiency. My nosebleeds had returned, too. "Your iron level is low," said the letter from my doctor, "and an over the counter vitamin will help. A low iron level needs to be worked up with a colonoscopy or other GI screening." That sounded not only uncomfortable, but expensive. I looked elsewhere for clues.
A search on Google Scholar turned up a study* involving coffee. "A cup of coffee reduced iron absorption from a hamburger meal by 39%..." I downloaded the full text. The study was done on humans, it stated what the subjects ate, and didn't sound like the researchers had any agenda. I'd been drinking more coffee--maybe that was my problem. Seeing if it made me feel any different wouldn't cost anything. So every day last week, I waited until two hours after breakfast to have coffee or tea (the study showed tea inhibited iron absorption even more than coffee). Within a few days, I felt like I had fresh gust of wind in my sails, and my nosebleeds mostly stopped. (Maybe coffee inhibits absorption of zinc as well.)
This seems to have worked well; I'll have another iron test in a few weeks when I donate blood. I don't even miss having coffee first thing in the morning.
"Inhibition of food iron absorption by coffee" by TA Morck, SR Lynch and JD Cook. American Journal of Clinical Nutrition, Vol 37, 416-420.