It's common for a parent to tell me that she has switched her baby to a low-iron formula, because the regular, iron-fortified one was causing constipation. "He's really much better, now," she reassures me. But I am not reassured.
Constipation is a bad problem, granted. But iron-deficiency is worse. In fact, there is a large and convincing body of research that links iron deficiency to long-term problems in brain development. A series of studies by Betsy Lozoff, M.D., has shown that babies who have low iron do worse all through school. And they continue to have more problems even into adulthood. They are less likely to graduate from high school, less likely to hold a job, less likely to have a happy home life.
Why is iron so important? Most people know that iron is a key ingredient in the blood. But iron also plays a vital role in the brain. Iron-containing enzymes are important for the normal break-down of neurotransmitters, the chemicals that convey information between brain cells. So it makes sense that there should be a connection between low iron and poor brain function.
Interestingly, human breast milk is pretty low in iron. But the iron in breast milk occurs in a form that is very easily and completely absorbed. By contrast, the iron in infant formula is very poorly absorbed. Most of it stays in the intestines, never getting into the baby's bloodstream. In order to make sure enough gets absorbed, the formula companies have to add lots of extra iron to the formula.
So, what is a parent to do? Breast feed, if you can. If not, use iron-fortified formula and deal with the constipation (more on that in another blog). By the way, researchers have not been able to show that there really is a connection between iron-fortification and constipation. In carefully done studies, babies fed high-iron formulas are no more likely to be constipated than babies fed low-iron ones. This is one of those areas in pediatrics - there are a few! - where most parents and most scientifically-trained MDs don't see eye to eye. For my part, I read the science, but I tend to believe the parents. They usually know best.