Iron
How much iron adults need, why plant sources absorb differently, and why supplements need a test first.
Last revised
A mineral essential to haemoglobin, which carries oxygen in the blood, and to many enzymes. Deficiency is the most common nutritional deficiency worldwide and a frequent cause of fatigue.
How much, and who needs more
UK reference nutrient intakes are 8.7mg a day for men and for women over 50, and 14.8mg for women aged 19 to 50, reflecting menstrual losses. Requirements rise in pregnancy and in growing adolescents. Heavy menstrual bleeding is the most common reason for deficiency in women of reproductive age, and is frequently normalised rather than treated.
Haem and non-haem
Haem iron, from meat, fish and poultry, is absorbed far more efficiently than non-haem iron from plants. Vegetarian and vegan diets can meet requirements but need more attention: pulses, tofu, fortified cereals, dried apricots, dark leafy greens and nuts are the main sources. Vitamin C taken with a meal substantially improves non-haem absorption; tea, coffee, calcium and phytates reduce it.
Why not to supplement blindly
Unnecessary iron causes constipation and nausea, can mask a serious underlying cause of blood loss by partially correcting the blood count, and is actively dangerous in haemochromatosis, an inherited iron-overload condition. A ferritin test first is the correct order.
Taking prescribed iron well
Absorption is best on an empty stomach with vitamin C, though taking it with food reduces side effects and is a reasonable trade if tolerance is the limiting factor. Alternate-day dosing is often as effective as daily and better tolerated. Dark stools are expected and harmless. Courses continue for around three months beyond correction, to refill stores.
At a glance
| Term | Detail |
|---|---|
| Reference intake, men and women over 50 | 8.7mg a day |
| Reference intake, women 19-50 | 14.8mg a day |
| Better absorbed form | haem iron, from meat and fish |
| Improves absorption | vitamin C in the same meal |
| Reduces absorption | tea, coffee, calcium, phytates |
| Test before supplementing | serum ferritin |
| Expected side effect of supplements | dark stools, constipation |
| Condition where extra iron is harmful | haemochromatosis |
When to get help
See a GP rather than self-supplementing if you are persistently tired, breathless on mild exertion, or have palpitations. Iron deficiency in men, or in women past menopause, requires investigation for a source of bleeding. Seek urgent advice for black tarry stools, visible blood in stool, or vomiting blood. Keep iron tablets away from children; overdose is a serious poisoning risk.
Where to go next
Where this comes from
- NHS - Iron in your diet
- NICE - Anaemia, iron deficiency clinical knowledge summary
- British Nutrition Foundation - minerals and trace elements
Medical disclaimer
This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to a GP, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 999.