How to take iron supplements

After a short hospital stay for a bleeding ulcer, 78 year-old Mabel was discharged home on pills to heal her ulcer and an iron supplement to correct her blood loss. Despite taking iron for 3 months, Mabel’s blood tests showed she was still low in iron. When I asked her which iron supplement she was taking, she proudly showed me a bottle of ferrous gluconate 300mg sustained release capsules. “The ferrous sulfate tablets they gave me tore up my stomach, so the pharmacist recommended this one. I can take one every day without a problem.”
Iron supplements have been used in medicine since ancient times. Greek physicians treated people who were pale and tired with drinking water enriched with iron, either created by leaving swords in water to rust or by saving the water blacksmiths used to cool hot iron in.
Iron is a critical part of hemoglobin, a protein responsible for carrying oxygen throughout the body, with four atoms of iron in each molecule giving blood its distinctive red color. Without enough iron to make hemoglobin, your body can’t supply enough oxygen and you’ll become pale and tired.
The most common cause of iron deficiency is blood loss, from stomach bleeding like Mabel experienced, heavy menstrual periods, or chronic blood loss from the intestines such as hemorrhoids. Less common causes of iron deficiency are poor diet, poor absorption due to gastric bypass surgery or kidney disease, or an increased need for iron during pregnancy or breast-feeding.  
We treat iron deficiency anemia by giving iron supplements to replace both iron in your blood and replenish iron stores in your bone marrow, usually by giving 100mg to 200mg of elemental iron daily over several months. The most common side effects of iron involve stomach or intestinal irritation: stomach pain, constipation, nausea, vomiting, and even diarrhea. Iron can also make your stools dark and cause a metallic taste.
The 3 most common forms of oral iron supplements are ferrous sulfate, ferrous gluconate, and ferrous fumarate. Ferrous fumarate contains 33% elemental iron, ferrous sulfate has 20% elemental iron, and ferrous gluconate has only 12% elemental iron.
Iron is poorly absorbed and needs an acidic environment to assist its absorption. Vitamin C (ascorbic acid) improves the absorption of iron by converting some of it from the less soluble ferric form to the more soluble ferrous form. A six- ounce glass of orange juice can improve iron absorption by 10%. Although they cause less stomach distress, enteric coated and sustained release forms of iron are not as well absorbed as rapid-release forms because they bypass the stomach to dissolve further down through the intestine where it is less acidic, so less of the iron is in the more absorbable ferrous form.
Taking iron supplements on an empty stomach either 30 minutes before or 2-3 hours after eating also increases iron absorption, although it causes more stomach irritation when taken without food.
Despite taking supplemental iron for 3 months, Mabel’s blood tests still showed iron deficiency anemia. I asked her which iron supplement she was taking, and she showed me a bottle of ferrous gluconate 300mg sustained release capsules instead of the ferrous sulfate 300mg tablets that she was originally prescribed. “The tablets they gave me tore up my stomach, so I’m taking these instead.” Each 300mg ferrous gluconate tablet only contained 36mg elemental iron instead of the 65mg in each 300mg ferrous sulfate tablet she was originally prescribed.  
Here are 6 Tips for Taking Iron Supplements Successfully:
1.The dose of elemental iron is the most important.
The effectiveness and side effects are similar at equal doses of elemental iron. 300mg of ferrous gluconate has 36mg of elemental iron compared with 65mg in 300mg of ferrous sulfate.
2.For best absorption, take iron on an empty stomach.
If taking your iron supplement on an empty stomach causes stomach irritation, try taking them with food instead of skipping doses.
3.Avoid sustained release or enteric coated iron supplements.
Sustained release, delayed release and enteric coated iron may cause less stomach upset but are less well absorbed.
4.Start by taking one ferrous sulfate tablet daily, increasing the dose if tolerated.
Higher doses of iron are not absorbed as well and cause more stomach upset and constipation.
5.Consider cooking with cast iron skillets and pans.
Cooking with cast iron increases iron content of your food and can treat mild iron deficiency.
6.Keep iron tablets out of the reach of children.
Both ferrous gluconate and ferrous sulfate tablets look like chocolate M&M candies.

Dr. Louise Achey, Doctor of Pharmacy is a 40-year veteran of pharmacology and author of Why Dogs Can’t Eat Chocolate: How Medicines Work and How YOU Can Take Them Safely. Your questions and comments are always welcome at www.AskDrLouise.com. 2019 Louise Achey