Health Reference LibraryHow much iron should I take, and how much is too much?
This entry is part of the Nutri Tailor Health Reference Library — cited research on supplements, nutrients and adjacent areas of health.
Summary
Only as much as a blood test says you need, because tiredness without a test is as likely to be iron overload as iron deficiency, and extra iron harms the person who already has plenty. For a low normal ferritin, 15 to 25 mg a day of a gentle form for eight to twelve weeks and then a retest is the usual approach. For diagnosed deficiency the GP sets the dose. The reference intake is 8.7 mg a day for men and 14.8 mg for women under 50, and the NHS says 17 mg a day from supplements is unlikely to cause harm. Above that, the decision sits with a GP, and iron must always be kept away from children.
Dose calculator: capsules to reach your iron target
Enter the daily amount of iron you are aiming for and see how many servings of each Nutri Tailor product reach it. Nothing you enter leaves this device. No AI is used.
This tool does arithmetic on the label figures. It is not personal dosing advice and it knows nothing about your history or blood results. The reference intake, the safe upper guide and the trial doses are on this page; talk to your GP or a registered nutritional therapist before changing what you take.
Effective dose
The reference intake is 8.7 mg a day for men and for women over 50, and 14.8 mg a day for women aged 19 to 50. Only what a blood test says you need. Without a test, do not take iron for tiredness, because the same symptoms occur in iron overload where extra iron does harm. For a low normal ferritin, 15 to 25 mg a day of a gentle form such as bisglycinate for eight to twelve weeks, then a retest, is the usual approach. For diagnosed deficiency the GP sets the dose, typically one ferrous salt tablet a day continued for three months after haemoglobin recovers, and alternate day dosing absorbs more per tablet.
Safety profile
How much is too much: the NHS says 17 mg or less a day from supplements is unlikely to cause harm; higher doses belong with a GP after a blood test. Iron is the common supplement most likely to poison a child; keep it out of reach, always. In adults, more than about 20 mg of elemental iron a day from supplements causes constipation, nausea and black stools, and sustained high intake without need raises stored iron. Above 17 mg a day only under a GP. Stomach pain that does not settle, or any bleeding, needs a GP the same week.
Guideline positions
NHS vitamins and minerals guidance for iron. NIH Office of Dietary Supplements fact sheet for iron where one exists. The trial doses quoted above are from the sources listed on this page.
Practical framework
Capsules to reach the dose, from the Nutri Tailor range, all made in the UK: [iron bisglycinate with vitamin C](/products/iron-vitamin-c), 15 mg of iron as bisglycinate with 400 mg of vitamin C per capsule, one a day sits inside the NHS guide. To read your own result against the UK ranges, use the free blood test result interpreter. This is a summary of published research, not personal health advice. Talk to your GP or a registered nutritional therapist before changing what you take, especially if you are pregnant, have a diagnosed condition or are under ongoing care.
Common misconceptions
That more iron works faster: above the doses the trials used there is no extra effect, only more side effects. That the front of the bottle states the dose: read the per capsule figure and the serving size on the back. That the NHS figure is a toxic threshold: it is the level below which harm is unlikely, which is a different thing.
Sources
- NHS 2026. Iron. Vitamins and minerals. NHS.
- NIH Office of Dietary Supplements 2025. Iron: Fact Sheet for Health Professionals. National Institutes of Health, Office of Dietary Supplements.
- National Institute for Health and Care Excellence (NICE, UK government) 2024. Anaemia - iron deficiency: Clinical Knowledge Summary. NICE Clinical Knowledge Summaries.