Women: underdiagnosed and tired - is it iron insufficiency?

Having insufficient iron levels is the most common nutritional issue worldwide, and women are disproportionately affected due to blood loss with each menstrual cycle, during which they lose an average of 16mg of iron.

Iron levels are measured through a blood test which checks your ferritin levels – your body’s store of iron.

The WHO’s recommendation for ferritin levels (used by Hong Kong’s Department of Health as a yardstick) say that anything above 15ug/L is acceptable – yet this number has been questioned for a decade, with scientists stating that it is ‘inappropriately low’.

The NHS cites different acceptable ranges for men (24-340ug/L) and women (11-310ug/L) despite stating that 12ug/L indicates a ‘complete absence of stored iron’.
Scientists say that women go widely underdiagnosed for insufficient iron levels, and that reference ranges are based on data collated from women who have low levels – which leads medical professionals to define insufficiency as ‘normal’.

Studies have recommended that the thresholds should be revised, with new lower limits including 25 ug/L, 40ug/L, 50ug/L, and even 100ug/L.

In one study, women who had ferritin levels lower than 50ug/L were given iron supplements, and experienced a significant improvement in symptoms like fatigue – demonstrating that the physical effects of depleted iron manifest at a much higher threshold than 15ug/L.

“I like to see ferritin levels of at least 50ug/L in clinic,” says Naturopathic Doctor Benita Perch. “When they drop below 50ug/L, symptoms like fatigue and brain fog start to manifest, as there isn’t enough iron to support oxygen delivery to tissues like the brain or muscles.”

“Around 80% of my female patients do not have high enough iron. It’s really important that women get their ferritin tested as part of their annual checkup,” says Benita.

Data suggests that if we adopted a more accurate threshold of 50ug/L, half of all women and around 14% of men would be defined as having insufficient iron levels. 

Why is iron insufficiency such a big problem?

Iron is key for creating red blood cells and haemoglobin, which transport oxygen from the lungs to all the cells in the body. That’s why the most common symptom of low iron is fatigue. It also comes hand in hand with mental health problems, brain fog, irritability, pale skin and shortness of breath. Hair loss, brittle nails and skin problems like dryness or spots are also symptoms.

It can be challenging to get enough iron from your diet – especially if you’re a vegetarian or vegan. A scientific review found that 12 to 79% of female vegetarians, and  1.7 to 29% of male vegetarians have less than 12ug/L of ferritin. If the threshold was instead 50ug/L, this number would be significantly higher.

Women are recommended to consume 18mg of iron per day; men and postmenopausal women are recommended 8.7mg; teen girls are recommended 14mg; teen boys 11mg.

Red meat is considered one of the best ways to consume iron – but 100g only contains 2.4mg, which is only 13% of a woman’s recommended daily intake.
And there are additional challenges, as many foods contain iron-inhibiting compounds which restrict the body’s ability to absorb the iron you’re consuming.

Frequent blood donations are a cause of iron insufficiency. The on-the-spot blood test they carry out to check if your iron levels are sufficient for donation is a serum iron test which is not reflective of your body’s total iron store. If you donate blood regularly, you should be getting your iron checked every 3-6 months.

While testing ferritin is a better measure of iron levels than a serum iron test, checks need to be more comprehensive than a singular ferritin test. “Ferritin is also an inflammation marker, and low ferritin levels can be masked by inflammation, which raise them to ‘normal’ levels,” says Dr Benita. “Doing a complete blood count and haemoglobin test gives me a full picture of iron levels.” 

How to take your iron supplement

You should take your iron supplement first thing in the morning 1-2 hours before eating breakfast, or taking any other supplement with minerals, including a multivitamin. 

“All minerals can compete with iron,” says Dr Benita. “Zinc is the biggest culprit, but calcium and magnesium can also affect absorption, so I recommend taking an iron supplement two hours before any other mineral. This gives the iron a chance to absorb in your digestive tract, without other substances inhibiting absorption. ”
Taking your iron with orange juice, a grapefruit, or a vitamin C supplement can help boost absorption.

Research has also suggested that taking an iron supplement every other day may increase absorption than taking it daily, as daily use can raise your levels of hepcidin which inhibits the absorption of iron.

Dietary sources for iron

Iron is found in both animals (haem iron) and plants (non-haem iron). Though spinach has a reputation for being iron-rich, it contains high levels of oxalic acid, which inhibits iron absorption. Most kinds of plant-based iron contain iron-inhibiting compounds, which is why vegetarians and vegans are often deficient.

When it comes to bioavailable iron, haem is best and organ meat is king, with an absorption rate of 25-30%. 85g of chicken liver contains 9.86 mg of iron – around 3.3mg of which is absorbed.

Mussels are also rich in iron, with 85g containing 5.7mg. Similarly, clams can be a rich source, but this depends on the type and processing. Studies have found whole baby, or baby clams are the best source, averaging around 30.5mg per 100g.

Eggs are sometimes cited as a good source of haem iron, but the yolk contains a protein called phosvitin, which inhibits iron absorption. The egg white also contains iron-inhibiting compounds. Eggs can inhibit iron absorption by up to 27% - so don’t eat these at the same time as taking iron supplements, or eating iron-rich meals.
Dark leafy greens like spinach actually only contain 2.7mg of iron in 100g, and with an absorption rate of 7-9%, you’re only absorbing around 0.216mg. Other plant-based sources of iron like grains have an absorption rate of 4%, and legumes a measly 2%. 

What shouldn’t you eat alongside iron-rich meals, or iron supplements?

Any foods or drinks which include iron inhibitors should be avoided for two hours either side of taking a supplement, or eating an iron rich meal. Lots of the compounds that inhibit iron absorption are rich in antioxidants and fibre, and contribute to a healthy diet. You shouldn’t aim to avoid these foods altogether, but you do want to time them right.

Sadly, this includes tea and coffee, both of which are high in tannins and polyphenols, which reduce iron absorption. Studies show that tea can affect iron absorption by over 85%.

Red wine, pulses, legumes, dark chocolate, berries and most fruits with skins, including apples, peaches and unripe bananas are all high in tannins. Virtually all fruits and vegetables contain polyphenols (a type of antioxidant) but those with the highest levels include peppermint, star anise, dark chocolate, berries, nuts, flaxseed, beans, artichokes, chicory and extra virgin olive oil.

Though some studies have debated whether calcium reduces iron absorption, a 2021 review of research verified that it inhibits both haem and non-haem iron sources. Calcium is found in dairy products like milk, yoghurt and cheese. Plant-based milks are also often fortified with calcium, as is bread. Tofu and fish with bones like sardines or salmon are also significant sources.

Phytates bind with minerals like iron and prevent their absorption. Foods high in phytates include grains, legumes, nuts, seeds and tofu. You can reduce the phytate content of these foods by soaking, sprouting or boiling them. Unfortified white sourdough is a good choice for bread as the fermentation process helps reduce phytates which are present in grains.

Foods high in oxalates, which includes root vegetables, potatoes, sweet potatoes, nuts and leafy greens like spinach can inhibit iron absorption.

Though tofu and tempeh are cited as good plant based sources of iron, they’re rich in soy protein – another iron-inhibitor.

Some medications, like antacids and antibiotics can reduce iron absorption.

Vitamin C enhances the absorption of iron as it forms a chelate which is better absorbed by the body, and is particularly effective for non-haem iron. Good sources of vitamin C include citrus fruits, kiwi, bell peppers, broccoli, cabbage, Brussel sprouts and tomatoes.

In summary

Don’t dismiss tired as your normal. Too often, women put down their symptoms as simply premenstrual tiredness, struggling to focus on the first day of your period, or ‘Mummy brain’.

Your symptoms are real and deserve attention – our naturopaths are here to find the root cause of your fatigue. Your concerns will be taken seriously, and we’ll rule out any conditions which share symptoms with iron insufficiency, referring you for tests to confirm a diagnosis.

If our tests confirm low ferritin levels, our naturopaths recommend Ferrochel Iron Chelate by Designs for Health, which has an exceptional absorption rate. Gentle on your tummy, this vegetarian formula doesn’t cause the digestive discomfort that other forms of iron can – constipation is a known (and dreaded) side effect of commonplace iron supplements.

Iron taken every other day on an empty stomach provides optimal absorption – and even better if you consume some kind of vitamin C alongside it, like a grapefruit, orange or fresh orange juice. Try to wait at least one hour until eating anything else, and two hours if you’re eating or drinking something which contains iron-inhibiting compounds, like milk, tea or coffee. 

References
NHS, Haem ferritin a guide for GPs, 2025
NIH, Iron
A Al-Naseem, Iron deficiency without anaemia: a diagnosis that matters, 2021.
NHS, Iron deficiency guidelines, 2024.
Z Mei et al, Physiologically based serum ferritin thresholds for iron-deficiency in children and non-pregnant women: a US National Health and Nutrition Examination Surveys (NHANES) serial cross-sectional study, 2021.
O Yaw Addo et al, Physiologically based serum ferritin thresholds for iron deficiency among women and children from Africa, Asia, Europe and central America: a multinational comparative study, 2025.
WHO, WHO guideline: use of ferritin concentrations to assess iron status in individuals and populations, 2020.
Department of Health, Thematic report on iron status: population health survey 2020-22.
K Martens, T G DeLoughery, Sex, lies and iron deficiency: a call to change ferritin reference ranges, 2023.
R Delfini Cancado et al, Defining global thresholds for serum ferritin: a challenging mission in establishing the iron deficiency diagnosis in this era of striving for health equity, 2025.
E Piskin, Iron absorption: factors limitations, and improvement methods, 2022.
J F Lai et al, Inconsistent values for iron content complicate recommending clams as an iron source, 2009.
E R Werner et al, The effects of 1 egg per day on iron and anemia status among young Malawian children: a secondary analysis of a randomized controlled trial, 2022.
R Pawlak et al, Iron status of vegetarian adults: a review of literature, 2016.
M Lazrak et al, Tea consumption reduces iron bioavailability from NaFeDTA in nonanemic women and women with iron deficiency anemia: stable iron isotope studies in Morocco, 2021.
J Deng, Efficacy of vitamin C with Fe supplementation in patients with iron deficiency anemia: a systematic review and meta-analysis, 2024.
D Skolmowska, D Glabska, Effectiveness of dietary intervention with iron and vitamin C administered separately in improving iron status in young women, 2022.
A Chaoui et al, Making bread with sourdough improved iron bioavailability from reconstituted fortified wheat flour in mice, 2006.
A Ibraheem Abioye et al, Calcium intake and iron status in human studies: a systematic review and dose-response meta-analysis of randomised trials and crossover studies, 2021.
A Melse-Boonstra, Bioavailability of micronutrients from nutrient-dense whole foods: zooming in on dairy, vegetables, and fruits, 2020.
N U Stoffel et al, Iron absorption from supplements is greater with alternate day than with consecutive day dosing in iron-deficient anemic women, 2020.