People who have anemia have been advised to cook in cast iron pans, because food does absorb iron while cooking.
Also, people who have medical conditions that require limiting iron intake have been advised not to use cast iron for cooking. I used to work with a hematologist and we had a few patients with Hemochromatosis who had to limit the amount of iron intake.
This is a from a good article on the subject:
This effect is so reliable that iron cookware has occasionally been used to combat anemia. A
variety of studies have shown that iron pots and pans can boost your iron status, substantially increasing the iron content of certain foods (like eggs and applesauce) but not others (like hamburgers).
[16][17] The pan’s iron is in the non-heme form, which isn’t absorbed as well as heme iron from meat. But vitamin C can greatly increase absorption, as can
acidity, so recipes containing things like lemon or tomato sauce can boost absorption.
examine.com