In brief. Iron helps carry oxygen around the body and contributes to normal energy-yielding metabolism, the normal formation of red blood cells and haemoglobin, and the normal function of the immune system. Some groups, such as women who menstruate and people who eat mainly plant-based foods, are more likely to have a deficiency; only a blood test arranged through a doctor can confirm this. Forms such as iron bisglycinate, iron sulphate and iron fumarate differ mainly in how gentle they feel and how well they are absorbed, while vitamin C increases iron absorption. Because too much iron is harmful and an overdose is dangerous for children, you should never take iron long term without medical advice. This is information, not medical advice.
What does iron do in the body?
Iron is an essential mineral, which means the body needs it but cannot make it itself and must obtain it from food. Most of the iron in the body is found in haemoglobin, a protein in red blood cells that binds oxygen efficiently in the lungs and releases it again in the tissues. This is why iron is so closely associated with oxygen transport and feeling physically well.
Iron contributes to normal oxygen transport in the body, the normal formation of red blood cells and haemoglobin, normal energy-yielding metabolism, normal cognitive function, the normal function of the immune system and the reduction of tiredness and fatigue, and it has a role in the process of cell division. These contributions describe what the mineral does as part of a normal, varied diet.
Who is more likely to have an iron deficiency?
Iron requirements vary from person to person, and some groups either lose more iron or simply need more of it. Women who menstruate lose iron through monthly blood loss, so their requirements are generally higher than those of men of the same age. This is not a reason for unnecessary concern, but it is a reason to be more mindful of intake. Pregnancy also increases iron requirements. People who eat little or no meat, including vegetarians and those following a plant-based diet, consume iron in a form that the body absorbs less efficiently than iron from meat, so they need to pay closer attention to their intake. Children, teenagers during growth spurts and regular blood donors may also have greater requirements. Belonging to one of these groups does not mean you have an iron deficiency; it only means that it is sensible to monitor your intake and discuss a test with a doctor if needed.
How is an iron deficiency identified?
An iron deficiency is something a doctor identifies with a blood test, not something you should infer from how you feel. Some people are tested because of general signs such as persistent tiredness, pale skin, shortness of breath during everyday exertion or brittle nails. These signs are not specific, which means they can have many causes unrelated to iron. The honest approach is to see them as a reason to ask a doctor for a blood test, not as a self-diagnosis and certainly not as a reason to start taking a high-dose supplement before you have been tested.
What are the best-known forms of iron?
Iron supplements use different iron compounds, which differ mainly in how well they are absorbed and how gentle they tend to be on the stomach. The overview below is for information.
| Form | Type | General characteristic (informational) |
|---|---|---|
| Iron bisglycinate | Chelated (amino acid, glycine) | Often described as gentle on the stomach and well absorbed |
| Iron sulphate | Inorganic iron salt | Widely used and well studied, harder on the stomach for some people |
| Iron fumarate | Organic iron salt | Contains a high proportion of iron, often used in supplements |
| Iron gluconate | Organic iron salt | Lower proportion of iron by weight, sometimes chosen for tolerability |
No single form is right for everyone, and no form is tolerated equally efficiently by everyone. Tolerability varies from person to person, and the right choice depends on the purpose, how well a particular form is tolerated and the advice you have received.
What about iron drops and the role of vitamin C?
Iron is also available as drops or a liquid, making the amount easy to adjust and potentially suiting people who prefer not to swallow tablets. The format itself is a matter of preference and convenience; what matters to the body is the type and amount of iron it provides. Vitamin C increases iron absorption, so iron is sometimes taken with a source of vitamin C or with a meal that contains it, allowing the body to use the available iron more efficiently. A drop or liquid format does not change what iron does in the body; it only changes how it is taken. See also our bioactive B complex with methylfolate and B12.
Is iron safe?
Iron is essential, but more is not better, and that is the most important point on this page. Unlike some nutrients, the body has no efficient way to eliminate excess iron, so even one dose that is too high each day can accumulate over time. Taking iron supplements you do not need, or taking high doses without medical advice, can be harmful and is not recommended. Common side effects of iron supplements include constipation, nausea and stomach discomfort, which occur more often at higher doses. Some people have conditions that cause the body to store too much iron, and extra iron is particularly risky for them. For all these reasons, you should not take iron long term without a blood test and medical advice. Iron supplements must also be kept out of the sight and reach of children because an accidental iron overdose in a child is a medical emergency. If you are pregnant or breastfeeding, take medication or have a medical condition, speak to a doctor or pharmacist first. Supplements are not a substitute for a varied diet or medical care.
Frequently asked questions
Which form of iron is gentlest on the stomach?
Tolerability varies from person to person. Iron bisglycinate, a chelated form, is often described as gentle on the stomach, while iron sulphate is well studied but can be harder on the stomach for some people. Which form is tolerated most readily is individual: no single form is equally efficient and gentle for everyone, and side effects such as constipation or nausea occur more often at higher doses.
Does vitamin C help with iron absorption?
Yes. Vitamin C increases iron absorption, an authorised relationship. This is why iron is sometimes taken with a source of vitamin C or with a meal that contains it. It does not change what iron does in the body; it helps the body absorb the available iron more efficiently.
What should I do if I feel tired and am considering iron?
Tiredness has many possible causes, and most have nothing to do with iron. The honest answer is to see persistent tiredness as a reason to ask a doctor for a blood test, not as a reason to start taking iron yourself. Iron should only be supplemented when there is a clear reason and preferably after a test.
Can you take too much iron?
Yes. The body cannot easily eliminate excess iron, so it can accumulate, and even one excess is harmful because the body cannot efficiently remove it. Taking iron you do not need or taking high doses without advice is not recommended. This is why iron should not be used long term without a blood test and medical supervision.
Why must iron be kept away from children?
An accidental iron overdose is one of the more dangerous poisonings in young children, and even a modest number of tablets can be serious. Iron supplements must always be kept out of the sight and reach of children, and any suspected overdose must be handled as a medical emergency.
Sources
- EU Register of nutrition and health claims made on foods (authorised claims for iron). Regulation (EU) No 432/2012. ec.europa.eu
- Regulation (EC) No 1924/2006 on nutrition and health claims made on foods.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on Dietary Reference Values for iron. EFSA Journal. 2015;13(10):4254.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinions on the substantiation of health claims related to iron. EFSA Journal.
- World Health Organization. Iron deficiency and anaemia. who.int
Written by the NOTFORTOMORROW editorial team. How we research: we base factual statements on the official EU claims register and on peer-reviewed and institutional sources, cite our sources and date our reviews. This article is information, not medical advice; speak to a qualified professional about your circumstances. Last reviewed: 2026-06-06.
