Green mussels and iron

Iron (for immunity support and energy production)

7 minutes to read
Tiana Hape-Cramond 1

Tiana Hape-Cramond

(Associate Registered Nutritionist)

Iron is an essential mineral that plays a pivotal role in our everyday existence, and is important for: 

  • Pregnancy and foetal development
  • Oxygen transport
  • Energy production
  • Brain health
  • Immune support
  • Temperature regulation

Iron can be found in both vegetables and animal products or supplementation.

In this article we explore iron, its function in the body, iron deficiency and more.

What is Iron?

Iron is essential for the production of red blood cells. Approximately 70% of the body’s iron is found in the red blood cells in the form of haemoglobin, and in the muscle as myoglobin. 

Haemoglobin is essential for transferring oxygen from the lungs to the tissues and myoglobin accepts, stores, transports and releases oxygen.[1]

Healthy infants are born with sufficient iron stores and can survive for 6 months before depleting their stores. The average human body has 3.5 grams of iron, 70% of which is haemoglobin.[2]

History behind Iron

Iron has been used by physicians to treat a variety of illnesses throughout history. In the 16th century iron was used to treat some disorders such as alopecia, tuberculosis, acne, gout, edema, fevers and more. 

Nicolas Lemery and Étienne François Geoffory are credited with demonstrating the presence of iron in 1713 but almost 2 centuries passed before metabolism of iron in the body was beginning to be understood.[3]

Reliable testing for blood haemoglobin was not created until 1875 and took years before it was widely accepted.[2]

Iron deficiency

Iron deficiency is one of the most common dietary deficiency globally. Factors that can cause inadequate iron levels are: 

  • blood loss
  • insufficient iron in the diet
  • poor absorption of dietary iron in the digestive tract
  • pregnancy[4]

A study suggested that in New Zealand approximately 10% of women and 1% of men have iron deficiency.[5]


Who is most at risk of iron deficiency?

Menstruating women

Teenage girls and women who have experienced heavy periods are at higher risk of developing iron deficiency as they are losing blood during their monthly periods.[6]

Pregnant women

Pregnant women are at higher risk of iron deficiency as they require twice the amount of iron. The increase in the need for iron is due to increased blood volume and for foetus growth.[6]


Infants, especially premature or low-birth weight, require iron to grow and develop properly. The iron that a full-term infant uses for the first 4 to 6 months of life is from the stores developed during foetal development

Infants that are premature or have low birth weights are at greater risk of iron deficiency as they do not have as much stored iron in their bodies.[6]

Individuals receiving dialysis

People receiving dialysis treatment may develop iron deficiency. This is due to the blood that is lost during dialysis and the kidneys no longer being able to produce erythropoietin which helps produce red blood cells.[6]

Gastric bypass

Individuals with a gastric bypass are at a greater risk of iron deficiency. This is due to the body being unable to absorb enough iron through diet.[6]

Individuals with certain dietary patterns

People who follow vegetarian or vegan diets are at higher risk of iron deficiency because of the elimination of heme iron-rich foods such as meat.

Those who follow high-fibre diets can also increase the risk of developing iron deficiency as large amounts of fibre can slow the absorption of iron.[6]

Different types of Iron

Heme Iron

Heme iron is found in animal based foods and is more easily absorbed. It’s predominantly in the blood and muscle (red meat and organs) but can be found in other sources such as mussels, oysters and clams and plant-based products derived from soy (e.g. Impossible Burgers).[7]

Non-heme Iron

Non-heme iron is iron found in plants. As it is less bioavailable compared to haem iron, it can be influenced by dietary factors.

Consuming vitamin C rich foods can enhance iron absorption

However, compounds such as phytates (found in wholegrains and legumes) and polyphenols (found in tea and coffee) can inhibit non-heme iron absorption.[8]

RELATED — Vitamin C (Immunity and Collagen booster)

Ferrous sulfate

Ferrous sulfate is an iron salt that is well absorbed in the body. This form of supplement provides a source of elemental iron that the body can use to replenish the body’s iron stores and support synthesis of new red blood cells.[9]

Ferrous sulfate is the most common prescribed iron supplement

Ferrous gluconate

Ferrous gluconate is a type of iron supplement that is used to treat or prevent iron-deficiency anaemia. Ferrous gluconate is a form of iron that is also easily absorbed in the body. It is available in tablets, capsules and liquid forms.[10]

Ferrous fumarate

Ferrous fumarate is a combination of iron and fumaric acid. It is best taken on an empty stomach, ideally one hour before eating or 2 hours after eating. It is available as tablets, capsules or liquid.[11]

Type of Supplement

Amount of elemental iron per tablet

Ferrous Sulfate

325 mg tablet (contains 65 mg elemental iron per tablet – hydrated. Contains 120 mg elemental iron in desiccated form)

Ferrous Fumarate

324 or 325 mg tablet (contains 106 mg elemental iron per tablet)

Ferrous Gluconate

324 mg tablet (contains 38 mg elemental iron per tablet)

Iron with a greater amount of elemental iron means more iron will be available to absorb.[12]

Health benefits of Iron

Iron has many functions which contribute to health benefits such as aiding in the formation of haemoglobin and cell production. 

Pregnancy and foetal development

Maternal-iron status has been linked to some neurological disorders and mental health disorders in their offspring. 

Low iron levels in the second trimester of pregnancy can increase the risk of the child developing schizophrenia by 30% and infants born with low serum ferritin concentrations have poorer recognition at birth.[13]

Iron Deficiency and Anemia in Pregnant Women
Iron Deficiency and Anemia in Pregnant Women
Source: Harvey, T. Assessment of Iron Deficiency and Anemia in Pregnant Women: An Observational French Study. (2016)

As maternal haemoglobin decreased the number of offspring with schizophrenia spectrum disorder increased.[14]

Oxygen transport

The main function of iron is the formation of haemoglobin, which is the protein in red blood cells that carries oxygen from the lungs to other parts of the body.[15]

A decreased saturation of haemoglobin in the blood leads to a decreased levels of oxygen in the blood.[16]

Iron and Transport of oxygen in the blood
Iron and transport of oxygen in the blood. The oxygen dissociation curve demonstrates that, as the partial pressure of oxygen increases, more oxygen binds hemoglobin. However, the affinity of hemoglobin for oxygen may shift to the left or the right depending on environmental conditions.

Energy production

Iron is a component of myoglobin, a protein found in muscle cells that stores and transports oxygen from muscle contractions. This is important for maintaining energy levels and physical performance.

It is seen in non-anemic male athletes that a low dose of iron supplementation can improve the symptoms of tiredness after exercise and provides relief from fatigue.[17]

Influence of iron supplementation on fatigue
Influence of iron supplementation on fatigue, mood states and sweating profiles of healthy non-anemic athletes during a training exercise.

Brain health

Iron is important for brain function as it plays important roles in: 

  • neurotransmitter homeostasis
  • myelin production
  • basal ganglia function[18]

It was found that if iron deficiency is present in the first two years of life it is associated with poor psychomotor performance, decreased response to stimuli and irritability.[19]

Immune system support

Iron is important for supporting the immune system, immune cell reproduction and maturation associated with the generation of specific response to infections.[20]

Research has found that low amounts of iron in the blood can inhibit immune responses to vaccines as t-lymphocytes require iron to support their metabolism. T-lymphocytes are important for destroying infected cells and helping antibody responses to infections.[21]

Temperature regulation

Iron plays a crucial role in temperature regulation due to its involvement in transporting oxygen and maintaining cellular respiration and energy production which influences body temperature. 

Iron-deficient individuals have an impaired response to cold temperature with rapid cooling body core temperature.[22]

Iron depletion and temeprature regulation
Thermogenesis and thermoregulatory function of iron-deficient women without anemia.

DNA synthesis

Iron plays an important role in the synthesis of DNA. Iron is involved in several biological processes. Iron acts as a redox element that functions as a cofactor in metabolic pathways including DNA metabolism, DNA repair enzymes and ribonucleotide reductase.[23]

Healthy skin, hair and nails

Iron is involved in oxygen metabolism and mitochondrial function which is important for normal growth and functional maturation of the skin and healthy hair and nails.[24]

In individuals with iron deficiency hair may become dry or fall out and nails may break more easily or change shape.[25]

Health claims that still need more evidence and research

Menstruation relief

Women with low iron could have lower haemoglobin and ferritin which can cause symptoms such as nausea, vomiting or tiredness during pre-menstruation.[26]

Research found that anaemia, production of lower–than-normal red blood cells, may be associated with dysmenorrhoea.

Dysmenorrhoea is described as painful cramps and can be accompanied by dizziness, cold sweating, and sometimes fainting.[27]

Taking an iron supplement may be able to alleviate some of the symptoms such as dizziness and prevent fainting. 

Iron deficiency and depression

The correlation between poor nutrition and depression has been explored before and the association between low levels of haemoglobin and low ferritin plasma levels in women with postpartum depression has been found.[28]

Iron deficiency and depression
Association between iron-deficiency anemia and depression.

The figure above shows more individuals with self-reported iron-deficiency anaemia scored 13 or more on the Kessler scale when compared to the control group of non-anaemic individuals.[29]

Best sources of Iron

Food Source

Concentration (mg/100g)

Daily Value (DV) Men / Women

Green Mussels

5.7 mg

71% / 32%


5.4 mg

67% / 30%


2.8 mg

35% / 15%

Fortified Cereal

2.7 mg

33% / 15%

Beef fillet steak

2.6 mg

32% / 14%


2.5 mg

31% / 13%

Chicken breast

2.0 mg

25% / 11%

Baked beans

2.0 mg

25% / 11%

Lamb steaks

1.9 mg

23% / 10%

Pork chops

0.9 mg

11% / 5%

Foods rich in iron

Important note — if you’re enjoying a daily mix of meat and vegetables, you should easily meet your iron demands.

Daily requirements and recommended Intake

The recommended daily intake (RDI) of iron changes throughout the lifespan. Babies, children and teenagers require more iron as they are rapidly growing. Women who experience periods require more iron due to the loss of blood each month.[30]


Male (RDI) 

Female (RDI)

7-12 months

11 mg/day

11 mg/day

1-3 years

9 mg/day

9 mg/day

4-8 years

10 mg/day

10 mg/day

9-13 years

8 mg/day

8 mg/day

14-18 years

11 mg/day

15 mg/day

19-50 years

8 mg/day

18 mg/day

50+ years

8 mg/day

8 mg/day

For pregnancy and lactation, the amount increases to 27 mg and 10 mg, respectively.

How to take Iron as a supplement

Iron can be given orally or intravenously. Oral supplements are the most common and easily accessible.

Iron infusions provide quicker improvements of iron-deficiency symptoms. Reasons for iron infusions include: 

  • individual can not tolerate iron taken orally
  • gut has issues absorbing iron (e.g. in people with inflammatory bowel disease)
  • blood loss makes it difficult to keep iron (e.g. after a severe injury)
  • to increase iron levels quickly
  • long term health issues which prevent the body using iron (e.g. rheumatoid arthritis or some types of cancer)
  • chronic kidney problems or heart failure[31]

Iron supplements should be taken on an empty stomach

This should be either 1 hour before or 2 hours after eating, with a drink containing vitamin C. 

However, to lessen the possibility of stomach issues, iron may be taken with or immediately after food.[32]

Common signs and symptoms of Iron deficiency

Iron is important for good health. The symptoms of iron deficiency include:

  • Weakness
  • Lack of concentration
  • Irritability
  • Fatigue
  • Shortness of breath
  • Pale skin
  • Dizziness
  • Heart palpitations
  • Headaches
  • Hair loss
  • Dry skin[25]

If you are experiencing any of the symptoms listed above please seek medical advice.

Iron risks and side effects

Iron can be found in many over-the-counter supplements. This availability means that iron toxicity can be common

Iron toxicity can also develop after several blood transfusions for chronic disorders such as thalassemia, sickle cell or haematological cancers.[33]

Acute ingestion of iron can be hazardous to children but if adult dosages of iron are ingested, it can be life-threatening. 

Ingesting too much iron can cause severe symptoms, liver damage and death. Symptoms include gastrointestinal upset (vomiting, diarrhoea and abdominal pain), while liver failure can develop days later.[34]

Common side effects from iron supplements include:

  • Dark or black coloured stool
  • Nausea
  • Constipation
  • Diarrhoea

Often these side effects improve as your body becomes accustomed to the supplement.[35]

Possible interactions with herbs and supplements

Supplements containing aluminium (some antacids), calcium, magnesium or zinc may reduce their intended purpose when taken at the same time as iron supplements. 

It is best to not take these within 2 hours of taking iron supplements.[36]

Possible interactions with medications

Taking an iron supplement may interact with other medications such as:

  • Tetracycline
  • Penicillin
  • Ciprofloxacin
  • Medications used to treat Parkinson’s Disease and seizures (for example phenytoin)

Medications that reduce stomach acid such as antacids impair iron absorption and may cause iron deficiency.[37]

Thyroid medications such as levothyroxine should be taken separately to iron supplements, since iron can interfere with the absorption of thyroid medication in the gut.[38]

Discuss with a medical professional if taking iron supplements is right for you.


Iron - health benefits, risks of deficiency and side effects

Key Takeaway — In this illustration we have outlined the most important information that you should know about Iron.

Related Questions

1. How can I raise my iron quickly?
Iron levels will increase as you begin to add more iron-rich sources into your diet. This can be done through foods, fortified foods such as cereals or supplementation.[39]

2. Does low iron cause weight gain?
Low iron may cause weight gain as energy levels will be low which can decrease your motivation for exercise and healthy eating.

Another way could be due to the low iron affecting thyroid function which can stimulate weight gain.[40]

3. Which vegetables are high in iron?
Iron-rich vegetables include:

  • Broccoli
  • Beans
  • Brussel sprouts
  • Kale.[41]

4. Can our body accumulate too much iron by eating too much meat?
Iron overload is when the body accumulates too much iron which is usually caused by the body’s regulatory system failing to keep iron at a healthy level.

Iron overload in healthy individuals is rare. However, it can occur in individuals that suffer from excess absorption of iron in the gut such as hemochromatosis.[42]

5. How long does it take for the body to adjust to taking iron in a supplement form?
Usually it can take up to 2 to 3 weeks of regularly taking iron supplements before symptoms improve.[43]

If you have any comments or questions, please let us know below. You can find more similar articles in our Nutrition section.

Tiana is an Associate Registered Nutritionist who has a passion for public health and education. Working towards a Master’s in Nutrition Practice with a Bachelor’s in Human Nutrition, Tiana has a personal interest in healthy heart nutrition and promoting positive lifestyle behaviours. 

Tiana is a part of the Content Team that brings you the latest research at D’Connect.


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