Iron - a comprehensive guide


Alongside calcium, iron is the mineral that everyone’s heard of. Iron is needed for carrying oxygen around our body to give us energy. It’s also involved in our immune system, and plays a role in cognitive function (thinking, reasoning, memory etc.). We only need a tiny amount of it, but it’s easy to fall short for a variety of reasons. Iron is found in two different forms in foods: ‘haem’ iron found in animal foods – which can be better absorbed – and ‘non-haem’ iron found in plant foods.

Primary functions of Iron

  • Iron helps to build red blood cells and haemoglobin to carry oxygen around the body. This makes it essential not only for energy, but for all the billions of chemical reactions in our body that require oxygen.
  • Iron also supports energy production in other ways: iron-containing molecules called cytochromes participate in the production of ATP, the primary energy storage compound in our cells. [1]
  • Iron is important for our immunity. It is needed for the proper function of our immune cells, and is involved in production of cytokines – immune chemicals that signal and direct the immune response. When iron is low, we are more susceptible to infections.[1,2]
  • Iron contributes to normal cognitive function – our ability to think, reason, learn and remember. In particular, iron deficiency is thought to affect cognitive development in young children.[4]

How much iron do we need?

The nutrient reference value for iron in the UK is 14 mg for adults. Nutrient reference values refer to the amount needed to ensure that the needs of nearly all the population (97.5%) are being met.

Food sources of iron

There are two primary types of iron found in foods.

Haeme iron is only found in animal foods. It is considered the better-absorbed form of iron, with up to 30% absorption rate [5].

Good sources of haeme iron include:

  • Liver – duck and goose liver come out among the highest, containing up to 31mg of iron per 100g! Next best are chicken, pork, turkey and lamb liver, providing between 10 and 20mg.
  • Shellfish – clams, oysters, cuttlefish and octopus. Clams can contain a huge 28mg per 100g, going down to about 5–7mg for octopus and oysters.
  • Beef and lamb meats (non-organ meats) contain up to 3 or 4mg of iron per 100g.
  • Fish – anchovies and sardines in particular, which contain around 3mg per 100g.
  • Duck is the highest in iron – duck breast may contain up to 5mg of iron per 100g. Chicken and turkey dark meat only provide around 2mg per 100g and breast meat even less – around 1mg.
  • Eggs contain about 1.2mg of iron per large egg.

Non-haeme iron is found in both animal foods and plants, but plants only contain this form. It is more poorly absorbed than haeme iron – some sources say only around 8–10 per cent is absorbed [5], others give a wider range. Absorption of non-haeme iron can be increased when eaten with haeme iron from animal foods.

The best sources of non-haeme iron include:

  • Green leafy vegetables – especially kale, providing up to 3mg per 100g; spinach, providing up to 2.7mg; and chard, providing 1.8mg.
  • Some varieties of potatoes with their skins can provide up to 3mg of iron per 100g (others provide less than 1mg).
  • Beans and pulses: kidney beans, mung beans, lentils and chickpeas provide between 6 and 9mg of iron per 100g – however because this is dry weight, this equates to about 2–3mg in a typical serving.
  • Pumpkin seeds and sesame seeds contain up to 15mg of iron per 100g, which equates to about 2mg per tablespoon.

Deficiency signs and symptoms*

Iron deficiency is the most common micronutrient (vitamin/mineral) deficiency in the world [3]. In the next section we discuss some of the possible risk factors and why some people are particularly susceptible to deficiency.  

Iron deficiency symptoms can include:

  • Fatigue, weakness
  • Anaemia
  • Pale skin
  • Dizziness
  • Poor appetite
  • Poor focus and concentration
  • Poor immunity
  • Sore tongue or ‘angular stomatitis’ (cracking and infection at the corners of the mouth)
  • Brittle nails, or spoon-shaped nails that curve outwards
  • Restless leg syndrome.

*If you experience any of these symptoms, please consult your doctor or health practitioner.

Contributing factors to iron deficiency

Poor iron intake from foods can obviously be a primary factor in having low iron levels. Vegetarians or vegans may be particularly susceptible because of a lack of the more easily absorbed haeme iron in their diet. Anyone on a restricted diet of any kind (e.g. for weight loss) may also be susceptible. Other factors that can put us at risk of deficiency include:

  • Heavy periods in women
  • Pregnancy, recent childbirth or breastfeeding
  • Low stomach acid
  • Gut conditions that affect mineral absorption, such as coeliac disease, Crohn’s disease or helicobacter pylori infection (a stomach infection)
  • Chronic or acute bleeding of any kind
  • Long-term use of aspirin or other anti-inflammatory medications
  • Medications that reduce stomach acid
  • Infants, young children and adolescents may also be at risk, as these are times of rapid growth.
  • Regular intensive exercise – athletes in particular may be susceptible.

As well as taking an appropriate iron supplement, the ideal way to address any iron deficiency is to work with your doctor or healthcare practitioner to determine and address the cause of your iron deficiency.

Iron toxicity/overload

Even though iron deficiency is more common, having too much iron can also be a problem. Iron is actually an ‘oxidant’, meaning it acts like a free radical; this means it can cause damage if levels are allowed to get too high in the body. Apart from people with hereditary haemochromatosis (iron storage disease), those most at risk of iron overload include men taking supplements containing iron – especially if they are also eating lots of foods that are rich in iron, such as red meat. [6] See ‘Dosages’ and ‘Safety’ below for further information and guidance.

Forms and bioavailability / What to look for when buying a supplement

Here are some of the primary forms of iron you may come across in supplements and prescribed iron tablets.

  • Ferrous sulphate is a form of iron that is often prescribed by doctors. For some people it may not be well tolerated and may cause constipation in the doses given.
  • Iron citrate, ferrous gluconate and ferrous fumarate are usually considered better-tolerated forms, and are commonly found in supplements.
  • Iron bisglycinate (sometimes labelled ‘iron amino acid chelate’) is considered one of the best supplement forms of iron. It is particularly gentle on the digestive system and should not cause or contribute to constipation. It is also considered a well-absorbed form: specifically, it’s been found that foods or drinks consumed at the same time may have less of an effect on the absorption of iron in the bisglycinate form when compared to absorption of iron in the ferrous sulphate form.[7,8]

In summary, iron bisglycinate (iron amino acid chelate) may be one of the best options to go for when choosing a supplement.

Additional ingredients or not?

Another good thing to look for in your iron supplement is vitamin C, which is known to improve the absorption of iron. Some iron supplements also contain B vitamins, which work with the iron to help build red blood cells. However, iron supplements do not need to contain these ingredients to be effective.

Dosages: Lifestyle Labs’ recommendations

Adult men / Post-menopausal women: Most adult men – and women after menopause – should not take iron supplements on a regular basis, unless they are currently deficient in iron or at risk of deficiency. This is because of the potential dangers of iron overload, as we saw above. A general adult multivitamin and mineral supplement providing up to around 10mg of iron a day is fine for most people. Most men’s and ‘seniors’’ multivitamins contain little or no iron.

Pre-menopausal women: Multis designed for pre-menopausal (menstruating) women often contain around 15–18mg of iron per daily serving. This additional iron is designed to replace what the woman loses during her menstrual period. More than this should not be taken unless you know you are deficient or at risk of deficiency.

Adults who are deficient in iron: If you are in the either of the two groups above and have had a blood test to show you’re deficient in iron (or you are at risk of deficiency), you will probably be advised by your doctor or healthcare practitioner to take an individual iron supplement. Dosages tend to start at around 15–20mg – this is generally considered a low to medium daily dose for someone who is iron-deficient. Higher-dose supplements can provide as much as 40–80mg of iron and are designed for those who have a more significant deficiency or who have been diagnosed with anaemia. If you are taking this higher level, it is advisable to get your iron level re-tested every two months to check on your progress.

Children: Children’s multivitamin and mineral and individual iron supplements may contain up to around 7.5mg of iron per daily dose. More than this may be recommended by a healthcare practitioner.

*When you’re comparing dosages of iron supplements, note that prescribed iron tablets often contain a milligram dose on the front of the label that does not correspond to the actual elemental iron content. For example, ‘Ferrous Sulphate Tablets 200mg’ refers to the total weight of the ferrous sulphate compound; the actual iron content is usually 65mg in this case. In contrast, over-the-counter iron supplements (such as those that we sell) are labelled with the actual (elemental) dose of iron, e.g. 20mg.


If you are taking any medications or have any medical condition, please consult your healthcare practitioner before taking an individual iron supplement.

Once again, please note that individual iron supplements should only be taken by those who are deficient in iron or are at risk of deficiency. See above under ‘Dosages: Lifestyle Labs’ recommendations’ for further guidelines.


  1. [This link leads to a website provided by the Linus Pauling Institute at Oregon State University. Lifestyle Labs is not affiliated or endorsed by the Linus Pauling Institute or Oregon State University.]
  2. Beard JL. Iron biology in immune function, muscle metabolism and neuronal functioning. J Nutr. 2001 Feb;131(2S-2):568S-579S; discussion 580S.
  3. Oppenheimer SJ. Iron and its relation to immunity and infectious disease. J Nutr. 2001 Feb;131(2S-2):616S-633S; discussion 633S-635S.
  4. Lozoff B. Iron deficiency and child development. Food Nutr Bull. 2007 Dec;28(4 Suppl):S560-71.
  5. Haas, E. and Levin, B. (2006). Staying healthy with nutrition. Berkeley: Celestial Arts. P.188
  6. Haas, E. and Levin, B. (2006). Staying healthy with nutrition. Berkeley: Celestial Arts. P.190
  7. Hertrampf E, Olivares M. Iron amino acid chelates. Int J Vitam Nutr Res. 2004 Nov;74(6):435-43.
  8. Bovell-Benjamin AC, Viteri FE, Allen LH. Iron absorption from ferrous bisglycinate and ferric trisglycinate in whole maize is regulated by iron status. Am J Clin Nutr. 2000 Jun;71(6):1563-9.


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      Dr. Lifestyle

      Dr. Lifestyle is our own collective of leading health, nutrition and fitness experts. Having several brains makes it really hard to decide what we feel like for breakfast (Chia Coconut Pudding, or a Green Smoothie?), but when it comes to health advice we are an all-knowing, hyper-intelligent, super human.