Iron deficiency is among the most common nutritional issues worldwide, impacting energy levels, concentration, and overall health. While iron supplements can be an effective solution, many people are unsure how to take them properly to get the best results.
If you are experiencing low iron levels, optimising how and when you take iron supplements can make a huge difference. In this post, we will dive into the best practices for iron supplementation by first outlining the types of iron supplements, followed by supplement timing, food and medication interactions and other valuable information to ensure your body absorbs the iron it needs.
How is Iron Absorbed?
Firstly, let’s break down the complex physiology of how iron supplements are absorbed.
- When you ingest an iron tablet it travels down your oesophagus, eventually reaching your stomach.
- The acidic environment of the stomach, assists the breakdown of the supplement, releasing the iron. The next step depends on the type of iron supplement you are taking.
- There are two main types of iron found in supplements: ferrous iron (Fe2+) or ferric iron (Fe3+). To absorb iron, iron needs to be in its reduced state which is ferrous iron. Therefore, supplements like ferrous sulfate, ferrous gluconate and ferrous fumarate provide iron in the ferrous form which does not require conversion for absorption.
- Ferric iron, on the other hand, found in supplements containing ferric citrate or ferric sulfate will undergo conversion with the help of stomach acid and a reducing agent like vitamin C.
- Ferrous iron will then move into the upper part of the small intestine which is where most of the absorption occurs. Enterocytes which are cells found in the lining of the small intestine have transporters called DMT1 which brings ferrous iron into the cell.
- The iron is then stored as ferritin or transported into the bloodstream via a protein called ferroportin.
Types of iron supplements
Oral iron supplements can come in tablet or liquid form. One isn’t necessarily better than the other.
Ferrous iron:
- Ferrous sulfate
- Ferrous gluconate
- Ferrous fumarate
Ferric iron:
- Ferric citrate
- Ferric sulfate
- Ferric pyrophosphate
As mentioned previously, ferrous iron does not require conversion as it is already in its reduced state. Iron bioavailability from ferric iron preparations is typically 3 to 4 times lower than that of ferrous sulfate. Ferric iron supplements however are still suitable, although pairing intake with a reducing agent like vitamin C will assist absorption.
The different forms of iron in supplements contain varying amounts of elemental iron. A standard dose of elemental iron ranges from 30-65mg. Ferrous sulfate has approximately 20% elemental iron, ferrous gluconate has 12% and ferrous fumarate has 33%.
For example:
The amount of elemental iron absorbed in the gut varies for each individual and can depend on factors such as haemoglobin levels and body iron stores. The amount of absorbed iron decreases as the iron deficiency is corrected.
How Much to Take?
Studies suggest that iron supplementation should be taken in doses of 60-100 mg of elemental iron on alternate days, rather than the traditional recommendation of 150-200 mg daily in divided doses.
This regimen avoids increasing hepcidin levels and improves iron absorption.
What is Hepcidin?
Hepcidin is a hormone produced by the liver that plays a role in controlling how much iron your body absorbs. When your body has enough iron, hepcidin acts as a “gatekeeper” to reduce iron absorption in the small intestines by preventing iron from entering the bloodstream.
Acute serum hepcidin persists for 24 hours after iron exposure. This means that serum hepcidin follows a circadian rhythm and timing influences the amount of iron absorbed.
What Can Inhibit Iron Absorption?
- Calcium-rich foods or drinks
- Phytates and polyphenols e.g. found in seeds, nuts, legumes and whole grains.
- Tannins e.g. coffee, tea and red wine.
- Antibiotics e.g. tetracycline
- Antacids e.g. proton pump inhibitors
Some natural compounds in plant foods can make it harder for your body to absorb iron. Two of the main ones are phytates and polyphenols.
Phytates are found in foods like whole grains, legumes, and nuts. Even small amounts can reduce how much iron your body takes in. For example, just 2 mg of phytates can lower iron absorption by around 18%, and higher amounts (like 250 mg) can reduce it by up to 82%.
Polyphenols, found in foods like red kidney beans, tea, and coffee, can also block iron absorption. Around 200 mg of polyphenols has been shown to reduce iron uptake by nearly 45%.
In simple terms, the more of these compounds you eat at the same time as your iron-rich foods, the less iron your body can absorb.
On the other hand, ascorbic acid has been found to counteract the inhibitory effects of phytates which is why consuming vitamin C-rich foods alongside iron-rich meals can significantly improve iron bioavailability.
Calcium can also affect how well your body absorbs iron, especially when it comes from dairy products or supplements.
Studies have found that drinks made with casein or whey (like milk-based drinks) containing around 100 to 200 mg of calcium can reduce iron absorption by 18 to 27%.
Larger doses of calcium may block even more iron from being absorbed.
This doesn’t mean you need to cut out calcium completely, but it’s a good idea to avoid having high-calcium foods or supplements at the same time as your iron-rich meals or iron tablets.
Tannins, found in beverages like tea and coffee, also impair iron absorption, with research indicating that high tannin intake during meals can reduce absorption by up to 50%. This effect underscores the importance of timing when it comes to tannin consumption.
Additionally, multivitamin pills containing iron, typically contain calcium, phosphorus and magnesium salts which can affect iron absorption. This is why multivitamins are not recommended as a sole therapy for iron deficiency and/or iron deficiency anaemia.
Lastly, while the research is not conclusive on the specific doses of antibiotics and antacids that inhibit iron absorption, it is still recommended to take these medications separately from iron supplements.
What Can Help Iron Absorption?
- Vitamin C
- Acidic foods like tomato sauce
- Fasted ingestion of iron supplements
When To Take Your Iron Supplement
Due to hepcidin increase, alternate-day dosing of oral iron supplements is more effective than daily dosing or twice-daily split dosing.
It is also recommended that iron supplements are taken between meals or at bedtime to avoid the “alkalising” effect of food, which means that certain foods can raise the pH level in the stomach. Iron supplements are best absorbed in an acidic environment. Therefore, foods like dairy products, calcium-rich foods or medications like antacids can reduce stomach acidity and impair iron absorption.
To prevent anything from interfering with absorption, it’s recommended to take iron supplements on an empty stomach, either 1 hour before eating, in the morning or 2 hours after meals and medications.
Some individuals may experience gastrointestinal discomfort when supplementing iron on an empty stomach, if this is you, taking your supplement with a small amount of food that does not inhibit absorption is suggested.
How Long Should You Supplement With Iron?
The duration of time spent supplementing with iron is dependent on how you respond to supplementation and the level of iron, to begin with. To monitor how iron supplementation is proceeding, this should be guided by blood tests (ferritin, haemoglobin) and checking in with your doctor.
What Can We Conclude?
While there are a wide array of iron supplements on the market, it appears that ferrous sulfate supplements have greater bioavailability than ferric iron supplements.
If ferric iron supplements are what you can get your hands on, don’t worry, just remember to pair your supplement with a rich source of vitamin C to ensure you are maximising your iron supplementation.
Due to hepcidin’s presence post-iron ingestion, it is recommended to consume your iron supplements every second day and preferably on an empty stomach.
