Most active people should only take an iron supplement after a blood test shows low iron, because the Australian Institute of Sport (AIS) says iron supplements should only be taken under medical supervision. Women who have periods, endurance athletes such as runners, and vegetarians and vegans are the most likely to run low, so it pays to know your numbers before you buy. Below: daily needs, iron for athletes, side effects and safety, vitamin C and forms such as bisglycinate.
How much iron do you need each day?
healthdirect lists these recommended daily intakes, from food and supplements combined:
| Group | Recommended daily intake |
|---|---|
| Men aged 19 to 50 | 8 mg |
| Women aged 19 to 50 | 18 mg |
| Adults over 50 | 8 mg |
| Pregnancy | 27 mg |
| Breastfeeding (19 and over) | 9 mg |
People on a plant-based diet need about 80% more, because plant (non-haem) iron is harder to absorb (healthdirect). The US National Institutes of Health sets the adult upper level at 45 mg a day, based on stomach and gut side effects.
So how much iron supplement per day? That is your doctor's call. When an athlete has low iron stores, the AIS framework typically uses about 100 mg of elemental iron a day, or every second day if it upsets the stomach, for 8 to 12 weeks, confirmed with a follow-up blood test. That is more than double the upper level, which is exactly why the dose belongs with your doctor.
Iron for athletes: why women and runners run low
The AIS says athletes are more susceptible to iron deficiency because exercise increases iron demand and there is limited opportunity to replace it from food. High-risk groups include:
- female athletes, because of iron lost during periods
- endurance athletes, including those training at altitude
- vegetarian and vegan athletes, because less iron is absorbed from plant foods
- athletes not eating enough to match their training (low energy availability)
A 2019 review found iron deficiency in roughly 15 to 35% of female athlete groups and 5 to 11% of male athlete groups, and highlighted exercise-induced rises in hepcidin, the hormone that controls iron absorption, as one contributing factor (Sim and colleagues).
Iron deficiency in runners often shows up as feeling flat, tired or unable to train as well as usual. The AIS links low iron to lethargy, fatigue and reduced training and performance, and healthdirect adds headaches, poor concentration, weakness or dizziness and more infections. These signs overlap with overtraining and illness, so a blood test is the only way to know. The AIS suggests testing at least serum ferritin, haemoglobin and transferrin saturation, ideally in the morning. Our supplements for runners guide covers race fuel.
Why the AIS says iron needs medical supervision
The AIS says iron supplements should only be taken under medical supervision as part of an integrated iron management program, which includes a dietary assessment and more iron from food. healthdirect gives the same advice. The reasons are practical:
- Tiredness has many causes. Your doctor needs to find out why your iron is low, including looking for unexpected blood loss (healthdirect).
- Too much iron is harmful. healthdirect says taking more than the recommended dose can cause iron poisoning and interfere with other minerals and your immune system. The AIS notes some athletes develop iron overload.
- Haemochromatosis. About 1 in 200 people has this genetic condition, which makes the body absorb and store too much iron (healthdirect). The AIS says people with haemochromatosis should avoid iron supplements.
- Children. Accidental overdose of iron products is a leading cause of fatal poisoning in children under 6 (NIH ODS), so store it out of reach.
Iron supplement benefits and side effects
If a blood test shows you are low, the benefits are real. Iron is needed for oxygen transport, energy metabolism, thinking and immunity, and low stores can affect endurance, mood, fatigue and how well you adapt to training (AIS). If your iron is normal, the AIS framework does not call for one: it is built for athletes with low iron diagnosed by blood tests.
Iron supplement side effects are mostly in the gut. The NIH lists stomach upset, constipation, nausea, abdominal pain, vomiting and diarrhoea, especially at 45 mg a day or more, and healthdirect notes iron can turn stools dark. Taking iron with food can reduce these effects (NIH ODS), although food also reduces absorption. The AIS says taking iron every second day reduces stomach upset without making it less effective over 8 to 12 weeks.
Iron also interacts with some medicines, including levothyroxine (the NIH advises 4 hours apart), levodopa and proton pump inhibitors, so check with your pharmacist.
How to take iron: vitamin C, timing and what to avoid
- Morning, near training: the AIS says taking oral iron in the morning, as close to exercise as possible, may improve absorption.
- Iron with vitamin C: the AIS suggests a source of about 50 to 100 mg of vitamin C, such as citrus fruit or juice, or a supplement that includes vitamin C.
- Keep tea, coffee and dairy apart: calcium and tannins reduce absorption, so the AIS advises avoiding them for an hour either side of your dose.
- Separate from zinc: the AIS lists zinc and manganese as minerals that compete with iron for absorption.
An honest note on vitamin C: in a 2020 trial of 440 adults with iron deficiency anaemia, iron tablets alone were as effective as iron plus 200 mg of vitamin C for haemoglobin and ferritin (Li and colleagues). A glass of orange juice with your dose is easy, but a separate vitamin C tablet is not essential.
Iron bisglycinate vs ferrous sulfate: which form?
Always compare elemental iron, the amount of iron itself, not the weight of the compound. The AIS says standard oral iron is a ferrous salt, and controlled-release iron may suit people who cannot tolerate ferrous salts.
| Form | Elemental iron by weight | Notes |
|---|---|---|
| Ferrous sulfate | About 20% | The standard medical option in the AIS framework |
| Ferrous fumarate | About 33% | Ferrous salt |
| Ferrous gluconate | About 12% | Ferrous salt |
| Ferrous bisglycinate | About 20% (18 mg from 90 mg on NOW's label) | Amino acid chelate; fewer gut side effects in pregnancy trials |
Salt percentages are from the NIH. In a 2023 meta-analysis of 17 trials, ferrous bisglycinate taken for 4 to 20 weeks led to higher haemoglobin and fewer gut side effects than other iron supplements in pregnant women, with no clear difference in children. The authors said more trials are needed in other groups, so evidence in athletes is limited (Fischer and colleagues). If ferrous salts upset your stomach, ask your doctor whether a bisglycinate or controlled-release product would suit you.
Products to look at (if your doctor recommends iron)
Use these only if your GP or sports doctor has recommended an iron supplement, and match the dose to their advice. Labels checked in October 2026.
- NOW Iron 18 mg: 18 mg elemental iron from Ferrochel ferrous bisglycinate per veg capsule, one a day with a meal.
- NOW Iron 36 mg: double strength, 36 mg from Ferrochel bisglycinate per capsule, vegan according to NOW.
- Thorne Iron Bisglycinate: 25 mg iron as bisglycinate per capsule.
Need a multivitamin without iron? Most picks in our best multivitamins guide contain none. Browse supplements for women and vitamins and minerals, and read our beef liver guide for a food-based option.
FAQs
Is it safe to take an iron supplement?
It is safe when a doctor has confirmed you need it and sets the dose. Without a blood test, iron can do more harm than good: too much can cause iron poisoning, people with haemochromatosis should avoid it, and iron products are a leading cause of fatal poisoning in children under 6. The AIS and healthdirect both say to take iron supplements only under medical supervision.
How much iron supplement per day should I take?
Only the amount your doctor recommends. Daily needs from all sources are 8 mg for men and adults over 50, 18 mg for women aged 19 to 50 and 27 mg in pregnancy. When athletes have low iron stores, the AIS framework often uses about 100 mg of elemental iron daily, or every second day, for 8 to 12 weeks under medical supervision, then a repeat blood test.
What is the best iron supplement in Australia?
The best iron supplement is the one your doctor recommends for your blood results. Ferrous sulfate is the standard medical option in the AIS framework, while bisglycinate forms may cause fewer stomach side effects, based mainly on trials in pregnant women. Compare elemental iron on the label rather than the compound weight, and take it the way your doctor advises.
Do athletes need iron supplements?
Not routinely. Athletes, especially female and endurance athletes, are more likely to run low, so regular blood tests make sense. The AIS says iron supplements should only be taken under medical supervision, with a dietary assessment as part of the plan, because more iron from food may be enough and too much iron can cause harm. Ask your GP or sports doctor about a ferritin test.
Is iron deficiency common in runners?
It is a known risk. The AIS lists endurance athletes and female athletes among its high-risk groups, and a 2019 review found iron deficiency in roughly 15 to 35% of female athlete groups. Hepcidin, a hormone that limits iron absorption, rises after exercise, which is one reason. If running feels harder than usual for no clear reason, ask your GP for a blood test.
Where can I buy an iron supplement online in Australia?
You can buy iron supplements online at Supps247 with Australia-wide delivery, which usually takes 2 to 8 business days, and free shipping on orders of $99.99 or more. You can also visit one of our 18 stores in Victoria and Queensland to compare labels. Stock varies by store, so check the product page first, and speak with your doctor before you start iron.
Sources: Australian Institute of Sport, iron (Sports Supplement Framework, Group A medical supplements); healthdirect, foods high in iron; healthdirect, iron deficiency; NIH Office of Dietary Supplements, iron fact sheet; Sim and colleagues (2019), iron considerations for the athlete; Li and colleagues (2020), vitamin C with oral iron, randomised trial; Fischer and colleagues (2023), ferrous bisglycinate meta-analysis.
Order online with Australia-wide delivery, free on orders of $99.99 or more, or visit a Supps247 store in Melbourne, regional Victoria or Brisbane to compare products in person before you buy. Members can use our member price match on full-priced items.
Always read the label and follow the directions for use. If you have a medical condition, are pregnant or take regular medication, check with your doctor first.
