Ask The Doctor: Iron and Cons... Health Article
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Mary Pickett, M.D., is a lecturer for Harvard Medical School and an assistant professor of medicine at Oregon Health & Science University in Portland, OR. At OHSU, she practices general internal medicine and teaches medical residents and students.
Question:
Why does taking iron cause you to be constipated?
Answer:
I laugh a little when people use the expression "I have an iron stomach." Iron is hard on the digestive tract. Constipation, nausea, gas or bloating occurs in about 10 percent of people who take iron supplements at a usual dose. The cause of the constipation is the iron itself, not any added ingredient.
It is hard to know exactly why iron is constipating, but what we know about iron may give us some hints. In its most basic form, iron is a metal that can carry an electric or magnetic charge. Also, it is chemically active, vulnerable to becoming "oxidized" (developing rust due to a chemical reaction). Perhaps this electrical and chemical activity affects the nerves and muscles in your bowel, slowing your normal bowel motion.
If you have constipation from iron, one excellent solution is to ask your doctor for a liquid form of iron supplement, such as the brand Feosol. You can then experiment by gradually lowering your dose until you get to a dose that does not cause you constipation.
You can also vary the amount of iron in your pill dose by changing the type of iron salt you are taking. Iron is paired up as a salt with a variety of other ingredients. If you take 300 milligrams (mg) of ferrous sulfate, you will get 60 mg of iron within each dose. If you take 300 mg of ferrous gluconate, you will only have 34 mg of iron in each dose. The ferrous gluconate dose is less constipating for many people; the trade-off is that it replaces your iron more slowly.
You may notice that you have less constipation if you take your iron with food. This is generally not recommended, because you won't absorb as much of your iron dose if you take it with your meal.
Slow-release forms of iron may be less constipating, but they have their downside. The very first part of your intestine (the duodenum and the first part of your jejunum) is where iron is absorbed best. A slowly releasing iron pill can travel past this area before releasing iron, so that you don't ever have a chance to absorb it.