Introduction

Iron is an essential mineral that is needed by the body for development and growth.¹ It must be derived from food sources and supplements, as the body cannot synthesise it. It has several uses in the body such as facilitating oxygen transport throughout the bloodstream via haemoglobin, and acting within myoglobin to store and release oxygen in muscle cells.² It is also required for neurological development, synthesising hormones, and cellular functioning.³ This article discusses iron’s role in the body- the causes and consequences of iron deficiency or overload.

How much iron should be in the body?

On average, the adult body stores between 1 g to 3 g of iron, where 75% of these are haem proteins, including haemoglobin, myoglobin, peroxidases, and cytochromes. The rest of the iron in the body exists as ferritin and hemosiderin, which are storage proteins.^2,4 These proteins belong in the liver, spleen, bone marrow, or myoglobin within muscle tissue. Transferrin is the main protein transporter in the blood that binds to the iron to deliver it to tissues.^3,4 

The intake of iron needed by the body depends on your age, your sex assigned at birth, and your diet. A vegetarian diet lacking meat, poultry, and seafood needs double the iron compared to a non-vegetarian diet. The body does not absorb haem iron and non-haem iron.¹ Haem iron is present in meats, poultry, seafood, and plant sources, whereas non-haem iron is only found in plant sources, such as nuts, dark chocolate, beans, fortified spinach, and grains. Haem iron has a much higher bioavailability than non-haem iron and is more readily absorbed.^2,3 In western populations, haem iron contributes 10% to 15% of total iron intake. A general guide to the amount of iron needed is:¹

• 14-18 year-olds assigned male at birth: 11 mg
• 14-18 year-olds assigned female at birth: 15 mg
• 19-50 year olds assigned male at birth: 8 mg
• 19-50 year olds assigned female at birth: 18 mg
• Adults 51+: 8 mg
•  Pregnant women: 27 mg
•  Breastfeeding women: 10 mg

Function of iron within the body

Iron has a variety of functions within the body and is a key micronutrient to enable proper growth, immune defence, and transport of oxygen.⁵ Arguably the most valuable function of iron is its role in erythropoiesis, as it is essential in forming new red blood cells. This is because iron makes up the haem groups within haemoglobin, the protein within the blood that oxygen binds to.⁶

Therefore, a lack of iron means a lack of haem groups and abnormal haemoglobin, limiting the oxygen transport around the body. After birth, all erythropoiesis occurs within bone marrow however iron is also used by every cell in the body.^6,7 This is because it is needed for regular metabolic function, development, and production of adenosine triphosphate.⁶ 

Research points to the main function of iron being erythropoiesis because the iron in the body is prioritised to red blood cells even over other major organs such as the heart, brain, and lungs.⁸ Besides, haemoglobin and adenosine triphosphate generation, iron is also associated with myoglobin, the immune system, and DNA synthesis.² Myoglobin has a very similar function to haemoglobin however, they are intrinsically different. While haemoglobin is within the blood and circulates oxygen around the body, myoglobin is often found within muscles acting as an intracellular store for oxygen.⁹

The similar role of both haemoglobin and myoglobin as temporary oxygen stores explains the shared presence of iron in both proteins. Iron content within the body also plays an important role in the immune response, this is because as mentioned, iron is essential for cell development. Therefore, if the immune system can restrict the available iron that a pathogen could utilise, the development of said pathogen would also be limited. This is known as nutritional immunity and is one of the roles of iron within the immune system. 

Iron also regulates immune cell growth and differentiation.¹⁰ It also acts as a cofactor for certain proteins essential in DNA replication and repair.¹¹ Without iron, these proteins would not activate meaning iron plays a role in many body functions. A reduced quantity of systematic iron would limit many of these functions but unfortunately, it is a condition that affects people.

Iron deficiency

Iron deficiency is the most common nutritional deficiency globally, affecting 30% of the population.¹² It is when red blood cells become smaller and contain less haemoglobin, therefore blood carries an inadequate amount of iron from the lungs to tissues in the body.¹ Causes of iron deficiency can include blood loss, a diet lacking in iron intake, or inadequate iron absorption.¹²

Blood contains iron, therefore losing blood causes iron levels to decrease. This blood loss can arise from individuals menstruating or gastrointestinal bleeding that can result from the overuse of painkillers.¹³ Malabsorption of iron is a disorder that affects the intestine’s ability to absorb nutrients. These disorders include celiac disease, Crohn’s disease, or tropical sprue.¹⁴ 

Signs of iron deficiency are associated with decreased oxygen delivery to tissues in the body, such as fatigue, pale skin, shortness of breath, rapid heartbeat, brittle nails, hair loss, dizziness, or headaches.¹⁵ If iron deficiency becomes severe, several complications can occur.

Heart complications or heart failure can occur as a result of a rapid heartbeat, subsequently leading to the heart pumping more blood to compensate for the lack of oxygen being transported. In children, severe deficiency can lead to delayed growth and development, and a higher risk of infections. In pregnant women, iron deficiency is associated with premature births and therefore low birth weight babies.¹³

Iron overload

While iron insufficiency causes internal issues, iron overload, at the other end of the spectrum also has consequences. Iron overload is an increase in iron intake across a significant time.¹⁶ It has many implications including liver disease, diabetes mellitus, arthropathy, hyperpigmentation, and cardiomyopathy.¹⁷ An excess of systematic iron can cause these clinical manifestations and multi-organ damage because iron catalyses the formation of harmful free oxygen radicals.^16,18

Iron overload is associated with liver damage because the liver is the main organ associated with iron storage, meaning excess iron will often cause a negative impact there. It has been suggested that the greater prevalence of diabetes mellitus in iron overload cases is due to an accumulation of iron in pancreas beta cells, leading to decreased insulin secretion.¹⁷

Arthropathy is correlated with excess iron within joints and is a somewhat common symptom of iron overload.¹⁹ Hyperpigmentation and cardiomyopathy occur due to excess iron deposits within the basal layer of the epidermis and the heart respectively.¹⁷ Maintaining iron homeostasis within the body is essential to preventing a series of negative clinical manifestations.

Maintaining healthy iron levels

For optimum iron, one should have a diet that includes iron-rich foods. These include lentils, nuts, seafood, beans, dark green leafy vegetables, dried fruit, poultry, red meat, lean meat, peas, or iron-fortified cereals.^1,13 These recommendations provide sources for both haem and non-haem iron. For absorbing iron vitamin C should be taken in conjunction with iron supplements or iron-rich foods.

It has iron chelating and reducing abilities, which allows the ferric iron to be converted to ferrous iron, which is more soluble. Additionally, vitamin C opposes iron absorption inhibitors like phytates in grains and legumes, calcium in dairy items, and polyphenols in tea and coffee.² To maximise iron absorption, these inhibitors should be avoided or taken with a source of vitamin C. These sources include broccoli, melons, oranges, strawberries, peppers, grapefruit, tangerines, kiwi, tomatoes and leafy greens.¹³

 Iron supplements are available to boost iron levels and should be taken under the guidance of a healthcare professional. Supplements can take the form of ferrous fumarate, ferrous sulfate, or ferrous gluconate which all vary in amounts of elemental iron. If an excess of iron supplements is taken, it can cause nausea, constipation, or other gastrointestinal side effects.³

Summary

Iron helps the body to perform multiple functions, including oxygen transport, energy production, and tissue function. If iron in the body is too low and too high adequate maintenance is required. This can come directly from iron-rich foods, having vitamin C with iron, avoiding iron absorption-inhibiting foods, and cautiously taking iron supplements. If you feel any symptoms of iron deficiency or overload, you should consult a healthcare professional.