What are the common misunderstandings about getting enough iron?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
Iron deficiency is the most common nutritional deficiency in the world, and in Japan too around 15–20 per cent of menstruating women are generally described as tending towards anaemia. Here we set the beliefs "spinach gives you iron" and "a supplement will sort it out" against what Japan's Dietary Reference Intakes actually say.
In numbers
| Item | Figure | Source |
|---|---|---|
| Recommended intake (menstruating women, 18–49) | 10.5 mg/day | Dietary Reference Intakes for Japanese (2025 edition) |
| Recommended intake (adult men) | 7.5 mg/day | Same as above |
| Actual intake (women in their 20s–40s) | About 6.5–7 mg, below the recommended amount | National Health and Nutrition Survey (2023) |
| Women with anaemia (haemoglobin below 12 g/dL) | About 15–20% of women in their 20s–40s | Various surveys |
| Absorption rate | Haem iron 15–25% / non-haem iron 2–5% | General figures in nutrition science |
| Tolerable upper intake | 40 mg/day for adults | Dietary Reference Intakes |
| Food (one typical serving) | Iron | Type |
|---|---|---|
| Pork liver, 50 g | 6.5 mg | Haem |
| Lean beef (round), 100 g | 2.7 mg | Haem |
| Asari clams (boiled), 30 g | 8.9 mg | Haem |
| Bonito (katsuo), 80 g | 1.5 mg | Haem |
| Natto, 1 pack (45 g) | 1.5 mg | Non-haem |
| Komatsuna (Japanese mustard spinach), 80 g | 2.2 mg | Non-haem |
| Spinach, 80 g | 1.6 mg | Non-haem |
| Hijiki seaweed (10 g dried, processed in an iron pot) | 5.8 mg / processed in a stainless-steel pot 0.6 mg | Non-haem |
[Verify] Check the recommended intakes against the 2025 Dietary Reference Intakes, the intake figures against the latest National Health and Nutrition Survey, and the food values against the Standard Tables of Food Composition in Japan (8th revised edition). The 2015 revision of the tables stated explicitly that hijiki values differ greatly by processing method.
Misunderstanding 1｜Spinach and hijiki are the kings of iron
Spinach iron is non-haem and poorly absorbed, and its oxalic acid hinders absorption. Hijiki's iron differs nearly tenfold by processing method (iron pot or stainless-steel pot), and most products today are made in stainless-steel pots. Red meat, fish and shellfish are the efficient sources.
Misunderstanding 2｜Just take a supplement
Too much iron is also a problem (upper limit 40 mg), and anaemia is not always caused by iron deficiency (bleeding, illness). If you have tiredness, breathlessness or dizziness on standing, a blood test comes first. For supplements, ask a doctor or pharmacist.
Misunderstanding 3｜Tea or coffee with a meal makes no difference to absorption
Tannins hinder the absorption of non-haem iron. Have green tea or coffee 30 minutes or more after the meal, or build meals around haem iron. Vitamin C (fruit, vegetables) helps the absorption of non-haem iron.
Misunderstanding 4｜Anaemia is only a women's problem
Growing children, older people, people who exercise hard and vegetarians also run short easily. Anaemia in men may have another cause, such as bleeding in the digestive tract, and is a reason to see a doctor.
Misunderstanding 5｜Cooking in an iron frying pan is enough
The iron that leaches out is small and varies with the dish and the cooking time (see our article on iron frying pans). Food is the basic source.
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Sources
- Ministry of Health, Labour and Welfare, *Dietary Reference Intakes for Japanese (2025 edition)* [日本人の食事摂取基準（2025年版）] (iron)
https://www.mhlw.go.jp/stf/newpage_44138.html
- Ministry of Health, Labour and Welfare, *Summary of results of the 2023 National Health and Nutrition Survey* [令和5年 国民健康・栄養調査結果の概要]
https://www.mhlw.go.jp/stf/newpage_47433.html
- Ministry of Education, Culture, Sports, Science and Technology, *Standard Tables of Food Composition in Japan (8th revised edition), 2023 supplement* [日本食品標準成分表（八訂）増補2023年] (iron in hijiki by processing method)
https://www.mext.go.jp/a_menu/syokuhinseibun/mext_00001.html
⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.
About this article
What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.
This is general information. Results vary from person to person and depend on your own conditions and surroundings.
Please decide for yourself, using your own judgement, whether any of this suits your situation. We cannot accept responsibility for any damage, loss or injury arising from following this article.
This article is not meant to diagnose or manage any specific medical condition. If you are worried about your health, see a doctor rather than relying on your own judgement.
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