Heme is an important molecule consisting of an iron atom embedded in a structure of porphyrin: 4 pyrroles, which are smaller rings made from 4 carbon atoms and 1 nitrogen atom. Heme is a cofactor for many reactions in the body, as well as a part of the important oxygen-carrying molecule: hemoglobin. Humans synthesize heme from dietary components in a complicated multi-step process involving over ten enzymes. Individuals who are deficient in iron or have mutations in any of these enzymes can experience compromised ability to make heme which results in anemia, or if genetic causes: Porphyria or Pyrrole disorder. This is actually a group of disorders that can affect the skin (cutaneous form) or a more acute version that affects the nervous system. The condition is somewhat rare and has extremely varied presentations. In addition, many parasites and gram-negative bacteria need the iron-containing cofactor, heme, to reproduce and cause infection. Parasites and bacterial pathogens must synthesize their own heme or acquire heme from the host. Thus, untreated chronic parasites and bacterial infections may create a heme deficiency.
In short, heme is an important cofactor that some individuals may be lacking due to a simple iron deficiency, chronic infection, or a more complicated issue of genetics. Heme does not exist in supplement form, but eating foods rich in heme and non-heme iron may help those with iron deficiency. People with diagnosed Porphyria disorders however are recommended to eat a low iron diet and therefore should avoid these foods as they are prone to iron-overload which creates increased oxidative stress.