Minerals in Pregnancy: Iron, Calcium, Iodine, Zinc and Magnesium and Official Advice
What health bodies say about iron, calcium, iodine, zinc and magnesium in pregnancy, what trials found for each, and why a midwife or doctor should guide any mineral supplement.
Content last updated . This page has not been medically reviewed.
Seek care first
- If anyone, especially a child, may have swallowed iron tablets or other mineral supplements, act at once. In the US call 911 or Poison Help at 1-800-222-1222. Outside the US see Poison help by country. The NHS says very high doses of iron can be fatal, particularly if taken by children. [1]
- Do not start, stop or change a prescribed supplement on your own. Ask your midwife, doctor or pharmacist. Pregnancy changes what is safe, and the right plan depends on your blood tests, diet and medicines.
The short answer
Health agencies agree that pregnancy raises the need for some minerals, but they differ on how much and on who needs a supplement. The NHS says it is best to get vitamins and minerals from food, and names folic acid and vitamin D as the supplements to take in pregnancy. [2] [3] The US MedlinePlus page lists iron and calcium among the nutrients needed in larger amounts. [4]This page covers five minerals. For vitamins and multi-nutrient products see Prenatal and postnatal vitamins. It is information only, not a plan for you.
What trials found
Evidence labels: established means a documented nutritional role and deficiency treatment; mixed, limited and insufficient describe how consistent or small the trial evidence is.| Mineral and question | What the source found | Strength |
|---|---|---|
| Iron, daily oral supplement versus placebo or none (57 trials, 48,971 women) | Less anemia at term and less iron-deficiency anemia at term; probably fewer low-birthweight babies; little to no difference in preterm birth. Certainty ranged from low to moderate. [15] | Established for anemia; limited for baby outcomes |
| Calcium versus placebo, to prevent pre-eclampsia (10 trials, 37,504 women) | Little to no difference in pre-eclampsia. Leaving out small studies, the result was high-certainty for no difference. [16] | No good evidence of benefit for this outcome |
| Iodine, routine supplements (14 studies, mostly mild to moderate deficiency) | Too little data to judge routine supplements; possible less postpartum hyperthyroidism and more digestive upset. [17] | Insufficient |
| Zinc versus placebo (25 trials, over 18,000 women) | Little or no difference in preterm birth; not enough evidence of benefit. [18] | Insufficient |
| Magnesium, oral supplements (10 trials, 9,090 women) | No clear difference in the main outcomes; not enough high-quality evidence. [19] | Insufficient |
| Magnesium for leg cramps in pregnancy | The pregnancy trials had a high risk of bias and could not be combined in a meta-analysis. [20] | Insufficient |
MedlinePlus says calcium during pregnancy can reduce the risk of pre-eclampsia. [4] The 2025 Cochrane update above did not find a clear effect in placebo-controlled trials, and said baseline calcium intake did not change its findings. [16] Agencies and reviews can differ, which is one reason to ask your care team what applies where you live.
Frequently asked questions
Do I need more minerals when I am pregnant?
Reference intakes for iron, calcium, iodine, zinc and magnesium differ in pregnancy, and the table above shows the published levels. [4] [10] Whether you need a supplement depends on your diet and blood tests, so ask your midwife or doctor.
Is there an upper limit for iron in pregnancy?
It depends on the body. Health Canada lists 45 mg a day for pregnancy. [12] EFSA did not set an upper level but gave a safe level of intake of 40 mg a day. [11] Do not use these numbers to plan your own supplement.
Does calcium prevent pre-eclampsia?
A 2025 Cochrane review of placebo-controlled trials found little to no difference in pre-eclampsia. [16] MedlinePlus states calcium can reduce the risk, so sources differ. [4]
Should I take iodine in pregnancy?
Cochrane found too little data to judge routine iodine supplements. [17] Iodine need is higher in pregnancy and too much can affect the thyroid, so talk to your midwife or doctor. [7] [13]
Will magnesium stop pregnancy leg cramps?
Proper evidence not found for a clear benefit. The Cochrane review of magnesium for cramps could not combine the pregnancy trials, and they had high risk of bias. [20]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Official intake levels in pregnancy
| Mineral | Reference intake per day | Upper level per day | Source and year |
|---|---|---|---|
| Iron | US: 27 mg for all pregnant women (RDA). EU: 16 mg, the same value EFSA lists for women before menopause | EU: no upper level set; EFSA gives a "safe level of intake" of 40 mg. Canada: 45 mg | MedlinePlus (US DRIs) 2025; EFSA 2017 and 2025; Health Canada 2025 |
| Calcium | US: 1,000 mg (age 19 to 50), 1,300 mg (14 to 18). EU: 1,000 mg (18 to 24), 950 mg (25 and over) | EU: 2,500 mg. Canada: 2,500 mg (19 to 30), 3,000 mg (18 and under) | MedlinePlus 2025; EFSA 2017 and 2025; Health Canada 2025 |
| Iodine | US: 220 mcg (RDA). EU: 200 mcg | EU: 600 mcg. Canada: 1,100 mcg (19 to 30), 900 mcg (18 and under) | MedlinePlus 2025; EFSA 2017 and 2025; Health Canada 2025 |
| Zinc | US: 11 mg (19 and over), 12 mg (14 to 18). EU: the non-pregnant value plus 1.6 mg | EU: 25 mg. Canada: 40 mg (19 to 30), 34 mg (18 and under) | MedlinePlus 2025; EFSA 2017 and 2025; Health Canada 2025 |
| Magnesium | US: 400 mg (14 to 18), 350 mg (19 to 30), 360 mg (31 to 50). EU: 300 mg | EU: 250 mg from supplements and added sources, not food. Canada: 350 mg from supplements only | MedlinePlus 2025; EFSA 2017 and 2025; Health Canada 2025 |
[5] [6] [7] [8] [9] [10] [11] [12]
The NHS gives general adult limits that apply outside pregnancy. It says 0.5 mg or less a day of iodine supplements, 25 mg or less of zinc supplements and 400 mg or less of magnesium from supplements are unlikely to cause harm for adults, and that iron intakes under 17 mg a day from supplements are unlikely to cause harm unless a GP advises otherwise. [13] [14] [1] These are not pregnancy-specific.
Cautions that matter in pregnancy
- Iron. The NHS says iron levels are checked at the booking appointment and at around 28 weeks, and that a GP or midwife will recommend iron if needed. [3] Iron overdose is dangerous to children. See Iron in pregnancy and the postpartum period and Iron overdose and child safety.
- Iodine. The NHS says high doses of iodine for long periods could change how the thyroid works. [13] Thyroid disease needs clinician guidance; see Iodine in pregnancy, breastfeeding and infant development.
- Vitamin A in mineral-containing products. The NHS advises against supplements containing vitamin A (retinol) and cod liver oil in pregnancy. Check labels of multi-ingredient products. [3]
- Medicines. The NHS lists calcium and iron supplements among products that may not mix well with levothyroxine. [21] Read Medication interactions and ask a pharmacist.
- Kidney or liver conditions. Extra magnesium is a particular concern with reduced kidney function. [9] See Minerals, supplements and kidney disease.
- Product quality. See Quality testing and certifications.
For food-first advice for women see Nutrition for women: iron, folate, calcium and vitamin D.
References
- NHS (UK). Vitamins and minerals: Iron. Page last reviewed 3 August 2020. Read 2026-10-23.
- NHS (UK). Have a healthy diet in pregnancy. Page last reviewed 21 April 2023. Read 2026-10-23.
- NHS (UK). Pregnancy vitamins and supplements. Page last reviewed 3 June 2026. Read 2026-10-23.
- MedlinePlus (US National Library of Medicine). Pregnancy and Nutrition (health topic summary). Read 2026-10-23.
- MedlinePlus (US National Library of Medicine). Iron in diet. Review date 1/21/2025. Read 2026-10-23.
- MedlinePlus (US National Library of Medicine). Calcium in diet. Review date 1/21/2025. Read 2026-10-23.
- MedlinePlus (US National Library of Medicine). Iodine in diet. Review date 1/21/2025. Read 2026-10-23.
- MedlinePlus (US National Library of Medicine). Zinc in diet. Review date 1/21/2025. Read 2026-10-23.
- MedlinePlus (US National Library of Medicine). Magnesium in diet. Review date 1/21/2025. Read 2026-10-23.
- European Food Safety Authority (EU), version 4, September 2017. EFSA, Summary of Dietary Reference Values. Read 2026-10-23.
- European Food Safety Authority (EU), version 11, August 2025. EFSA, Overview on Tolerable Upper Intake Levels (SCF and EFSA NDA Panel), Tables 1 and 2. Read 2026-10-23.
- Health Canada, Dietary reference intakes tables: Reference values for elements, page dated 2025-11-19. Read through the WebFetch tool, whose output is a model-made extract of the table, so these figures should be treated as (WebFetch extract). Read 2026-10-23.
- NHS (UK). Vitamins and minerals: Iodine. Page last reviewed 3 August 2020. Read 2026-10-23.
- NHS (UK). Vitamins and minerals: Others (magnesium, potassium, selenium, zinc and others). Page last reviewed 3 August 2020. Read 2026-10-23.
- Finkelstein JL et al. Daily oral iron supplementation during pregnancy. Cochrane Database Syst Rev 2024;8:CD004736. PubMed abstract (PMID 39145520). Read 2026-10-23.
- Cluver CA, Rohwer C, Rohwer AC. Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems. Cochrane Database Syst Rev 2025;12:CD001059. PubMed abstract (PMID 41330480). Read 2026-10-23.
- Harding KB et al. Iodine supplementation for women during the preconception, pregnancy and postpartum period. Cochrane Database Syst Rev 2017;3:CD011761. PubMed abstract (PMID 28260263). Read 2026-10-23.
- Carducci B, Keats EC, Bhutta ZA. Zinc supplementation for improving pregnancy and infant outcome. Cochrane Database Syst Rev 2021;3:CD000230. PubMed abstract (PMID 33724446). Read 2026-10-23.
- Makrides M et al. Magnesium supplementation in pregnancy. Cochrane Database Syst Rev 2014;4:CD000937. PubMed abstract (PMID 24696187). Read 2026-10-23.
- Garrison SR et al. Magnesium for skeletal muscle cramps. Cochrane Database Syst Rev 2020;9:CD009402. PubMed abstract (PMID 32956536). Read 2026-10-23.
- NHS (UK). Levothyroxine (medicine page). Page last reviewed 6 July 2026. Read 2026-10-23.