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Do Iron Supplements Make You Feel Sick?
Iron is one of the most important dietary minerals. (1) Its key role is to bind hemoglobin to allow your blood to carry oxygen from the lungs into your tissues. Iron also has a significant role in the function of macrophages, which are immune cells that clean up dead and dying cells from your body.
Iron deficiency is a leading cause of illness in the developing world, causing anemia, fatigue and immune system dysfunction. Long-term iron deficiency can also lead to depression.
Iron deficiency is most common in young menstruating women and vegetarians. Women, because they lose iron in their menstruation every month, and vegetarians and vegans, because the iron in vegetable products is harder to absorb than that in animal products. (2)
For this reason, many people are prescribed iron supplements. However, somewhat ironically, the most common iron-related problem today is not iron deficiency, but iron overdose.
Can You Overdose on Iron?
It is important to remember that while having enough iron supports your bodily functions, an excess does not improve these functions. Too much iron can be even more detrimental 
than not enough. (3) Chronic iron overdose, such as through increased absorption or too high a dose, can cause fever, headache, bluish skin and organ oxidation.
Acute poisoning, seen most often in young children who accidentally gain access to a pill bottle, can cause bloody vomiting and/or bloody stools, fluid in the lungs (also known as pulmonary edema), low blood pressure, nausea, liver damage and shock.
So certainly, yes, iron supplements CAN make you sick, especially if you take too much or not enough.
How Much Iron Should You Consume Daily?
The recommended daily allowance (RDA) of iron is based on your age, gender and lifestyle. (4) Ask your doctor about the specifics, but a man will need about half the amount of iron as a menstruating woman over 18. Pregnant and
lactating women need more iron as well.
Someone who occasionally donates blood will also need more iron than someone who does not, similar for a person who exercises heavily.
Iron RDA (A handy list to use as a guideline):
- 8 mg for men and non-menstruating women
- 9 mg for lactating women under 19
- 10 mg for lactating women over 18
- 15 mg for menstruating women under 19
- 18 mg for menstruating women over 18
- 27 mg for pregnant women
Keep in mind that RDAs include the amount you get from your diet. Ask your medical provider whether your lifestyle warrants an iron supplement.
Interestingly, though, being over or under on your RDA of iron isn’t the only way iron can make you feel sick. The number one reason for noncompliance (that means not doing what your doctor says) when prescribed iron supplements, is the increased chance of side effects associated with many forms of iron.
Some people experience stomach pains, nausea, constipation or diarrhea when on certain forms of iron. (5) This often leads to stopping the pills and never getting their iron levels up to where their doctor wants, and continued symptoms of iron deficiency.
A Note on the Absorption of Iron
First of all, why do these side effects occur? Your body is very slow to absorb iron, which is a good thing, considering the severe effects of iron overdose. However, research shows that the longer iron sits in your stomach and intestines, the more irritation is experienced.
Iron absorption in the digestive tract occurs for about 48-72 hours before the cells responsible for absorption are shed as part of the natural process of digestion, taking with them any unabsorbed iron. This transit of iron through the intestine can add to irritation of the intestinal tract and the bowel complications mentioned above.
Bioavailability of Iron
Different forms of iron are absorbed at different rates. This is a concept known as bioavailability. Iron comes in two basic forms, ferrous (2+ oxidation state) and ferric (3+ oxidation state). (6) This is important because iron is only bioavailable in its ferrous form, so if you take a ferric iron supplement, it will have to be converted in the GI tract prior to being able to absorb. This increased time in the GI tract leads to more irritation and subsequently more side effects.
The most bioavailable form of iron is carbonyl iron, which is closest to the elemental form, followed by the various forms of ferrous salts. (7) Ultimately, the main point is that the closer to elemental iron, the more bioavailable and the higher percentage absorbed in the GI tract.
How to Reduce Side Effects of Iron Supplementation
1. Increase absorption of iron with vitamin c
This is the most direct way to reduce side effects because it addresses the primary cause. Vitamin C increases the absorption of non-heme iron, and can even reverse the inhibiting effects of calcium and coffee or tea. (8) Many doctors suggest taking your supplements with orange juice, and some forms of iron supplements come with vitamin C added for this very reason.
It is not recommended to take the supplement with food, coffee, tea or fiber because this can significantly reduce absorption and may make nausea worse initially, but some people do report decreased stomach pain if they take iron with a meal. Drinking more water (to speed GI transit time and optimize cellular function) is also reported to be very effective in reducing side effects of constipation and stomach pain.
2. Acclimate your system slowly
Some people find that if they start slowly, their body gets used to the iron and they do not suffer as many side effects. Try spreading out your doses.
Start with half the recommended dose spread out into several doses throughout the day, then gradually increase to the full dose. Make sure to tell your doctor if you plan to do this and get the go-ahead from her or him.
3. Change your supplement
There are many different classes of supplements that offer different amounts of elemental iron, dosing regimens, and bioavailability. Additionally, they come in various forms, from capsules to tablets to powder and you may find that you tolerate some forms better than others. Slow release tablets, though they often come in higher doses, are also more tolerable for some people. (9)
Each person has difference levels of tolerance and there is no single supplement that is best for every person. It usually takes some trial and error to find one that works best for you, meaning it helps you meet your needs and has minimal side effects. Always keep your doctor updated on your side effects so they can best help you manage them
4. Adjust based on how you feel
Using fiber to alleviate diarrhea or a stool softener to alleviate constipation may be enough for mild signs, but, again, check with your doctor first to make sure there is no negative interaction between medications.
The most critical point to keep in mind is that over supplementation of iron is dangerous and you should not try to play doctor and adjust your dose or form of iron on your own to avoid unwanted side effects.
When Is the Best Time to Take Iron Supplements?
Iron supplements are best absorbed fasted or on an empty stomach, however if you feel nauseated, experience stomach pains or cramping, or if you vomit, take iron an hour or two after meals instead. This will allow your blood sugar levels to return to normal, but the food in your stomach will create a buffer that will aid iron absorption.
Avoid take coffee, tea, dairy products, or antacids within two hours of taking this medication so as not to decrease its effectiveness. Always drink at least 8 ounces of water with your iron supplements, and do not lie down directly after take them. Do not chew or crush capsules, especially slow-release capsules. This can cause the release of it all at once, increasing the likelihood of side effects.
Take tablets or capsules with a full glass of water (8 ounces or 240 milliliters) unless otherwise directed by your doctor. Do not lie down for 10 minutes after taking your tablet or capsule dose. If you are taking iron supplements in liquid form, always use a measuring spoon or cup.
The Final Word
Iron supplements are not supposed to make you feel sick, but depending on the type of iron supplement that you use, combined with individual variables, there are cases where side effects such as nausea, stomach pain, stomach cramps, diarrhea, constipation, vomiting or headache may occur.
Do not let this deter you from following the RDA. Sometimes iron supplementation without the unwanted side effects is just a matter of finding the right time to take it, taking the mildest or gentlest form, and eating the right foods alongside it to maximize its benefits.