Everything you need to know about iron supplements

Liquids, capsules, gummies – when it comes to iron supplements, the choices can feel overwhelming. With so many options available, how do you know which one is right for you?

If you're thinking of taking an iron supplement, this guide will help you find the best one for you.

This article answers:

• Who should take an iron supplement?
• How do iron supplements work?
• What are the disadvantages of an iron supplement?
• Which type of iron supplement is best for me?

Who should take an iron supplement?
 

You might benefit from iron supplements if you are:

• Diagnosed with an iron deficiency or anaemia
• Pregnant, breastfeeding, or experience menstrual cycles
• Vegan or vegetarian
• A woman under the age of 50
• An athlete, especially a runner
• Unable to maintain healthy iron levels through diet

The easiest way to figure out if you need an iron supplement is to consult with your GP. If you would rather check your iron levels at home, an Iron Blood Test or Advanced Iron Blood Test could be a good option for you.

If your iron levels are low and can't be explained by your periods or diet, it's important to see your GP for an assessment. This is especially true if you have any blood in the stools, a change in your bowel habit, or if your levels don't improve with supplements. 

How much iron do I need?

The recommended intake of iron varies depending on your age and sex.

Typically:

• 7mg a day for men aged 19 and over
• 8mg a day for women aged 19 to 49
• 7mg a day for women aged 50 and over

Iron supplements available in shops tend to have 18 to 65 mg of iron. If you go to the doctors, they might prescribe you something a bit higher. It's really important to stick to your recommended dosage in order to avoid iron overload.

How do iron supplements work?
 

You’ll usually find iron supplements with ionic iron – either ferrous (Fe²⁺) or ferric (Fe³⁺) iron. Ferrous iron tends to be more bioavailable which is good for raising your iron levels, while ferric iron may be better for maintaining your iron levels, rather than boosting them.

Iron is absorbed in the small intestine and stored in a protein called ferritin (you can learn about the difference between ferritin and iron in our blog). From there, the iron is either kept in storage or transported to bone marrow to create more red blood cells.

How to optimise iron supplement absorption:

• Take iron supplements in the morning – your levels of hepcidin (an absorption-limiting protein) are lower in the morning than the evening [1] so the theory is the iron uptake will be better.
• Avoid taking iron with a cuppa – antioxidants found in tea and coffee really like to bind with ferrous iron so they can’t be stored in ferritin.
• Avoid mixing iron and dairy products – calcium is thought to limit iron absorption, including all dairy products, leafy greens such as broccoli or cabbage, and tofu [2].
• Look for supplements containing vitamin C, or take them with a glass of orange juice for maximum iron absorption.

How long does it take for an iron supplement to work?

It usually takes three to four weeks for an iron supplement to work but can take two to four months to feel the full effects. You’re recommended to retest your iron levels three months after beginning supplements, to see if positive changes have happened.

Are there disadvantages to taking iron supplements?
 

Most people tolerate iron tablets well, but like any supplement, there can be side effects, such as cramps, nausea, constipation, and diarrhoea.

Although it’s better to take iron supplements in the morning on an empty stomach, you may find this gives you the side effects. Taking iron supplements with food can prevent this, just be mindful of what food you are taking it with [5]. Another option is to take iron at night just before bed, preferably two hours after eating.

Which type of iron supplement is best for me?
 

There’s many types of iron supplements available, each containing varying amounts of iron, available in different formats, and with different benefits and advantages. Generally, iron that comes in solid form tend to be best for boosting your iron levels, while liquid irons are better for maintenance and gentler on the stomach.

So, which iron supplement is best? Everyone has different preferences, we’ll leave it to you to decide!

Best for low budgets: Ferrous sulphate
Best for sensitive digestion: Ferric pyrophosphate
Best for fewest side effects: Ferrous gluconate
Best for varied formats: Ferrous fumarate
Best for maximal absorption: Iron bisglycinate
Best for iron maintenance: Ferric salt sprays
Best for easy dosing: Iron-rich water

References

1. Schaap CCM, Hendriks JCM, Kortman GAM, Klaver SM, Kroot JJC, Laarakkers CMM, et al. Diurnal rhythm rather than dietary iron mediates daily hepcidin variations. Clin Chem. 2013;59: 527–535. doi:10.1373/clinchem.2012.194977
2. Food for healthy bones. In: nhs.uk [Internet]. 18 Jan 2022 [cited 7 Mar 2025].
3. Christides T, Wray D, McBride R, Fairweather R, Sharp P. Iron bioavailability from commercially available iron supplements. Eur J Nutr. 2015;54: 1345–1352. doi:10.1007/s00394-014-0815-8
4. March 2006 PB. Any old iron? In: RSC Education [Internet]. [cited 12 Mar 2025].
5. About ferrous sulfate. In: nhs.uk [Internet]. 10 Feb 2023 [cited 12 Mar 2025].