Mineral Side Effects Quick Reference: Common Reactions by Mineral and When to Seek Care
A table of reactions reported with too much calcium, magnesium, zinc, iron, potassium, selenium, iodine and other minerals, with what the sources say and when to ask a clinician.
Content last updated . This page has not been medically reviewed.
Start here
If a child has swallowed mineral supplements, or anyone has severe symptoms after taking a large amount, call Poison Help at 1-800-222-1222 (US) or 911 in an emergency. [1] This page is a quick map of reactions that public-health sources link to too much of each mineral. It is information only. Most minerals have a Tolerable Upper Intake Level (UL), and most side effects come from supplements rather than food, so check Mineral Toxicity: Which Minerals Have Upper Limits for the detail.How to read the table
The NHS figures below are the UK Department of Health and Social Care guidance as printed on NHS pages last reviewed in August 2020. They are supplement amounts per day, and the pages do not say whether they are elemental mineral or compound weight, so do not compare them with a label until you have checked. Other countries set different levels. Evidence is of the type "public-health guidance", not a trial of each reaction.Reactions reported by mineral
| Mineral | Reactions the sources report with too much | Who is more at risk | When to ask a clinician or pharmacist |
|---|---|---|---|
| Calcium | The NHS says more than 1,500 mg a day could lead to stomach pain and diarrhoea. [2] MedlinePlus says higher amounts over a long period raise the risk of kidney stones in some people. [3] | Some people; the source does not say who | Stomach pain that continues, or a stone history |
| Magnesium | The NHS says more than 400 mg for a short time can cause diarrhoea. [4] | MedlinePlus says side effects are not common except in people with significantly reduced kidney function. [5] | Any kidney condition, or if you use magnesium-containing laxatives [5] |
| Zinc | MedlinePlus lists diarrhea, abdominal cramps and vomiting. [6] Long-term excess can lead to copper, iron or magnesium deficiency. [6] The NHS says high doses reduce copper absorption, which can lead to anaemia and weakened bones. [4] | People taking zinc for long periods | Before taking more than the NHS level of 25 mg a day. [4] Zinc nasal sprays and gels may cause loss of smell. [6] See Zinc Nasal Sprays and Gels |
| Iron | The NHS lists constipation, feeling sick, being sick and stomach pain at high doses (over 20 mg). [7] | Children: very high doses can be fatal. [7] | Call Poison Help for a child. [1] See Iron Supplement Side Effects |
| Potassium | The NHS lists stomach pain, feeling sick and diarrhoea. [4] MedlinePlus says too much potassium in the blood (hyperkalemia) may cause abnormal and dangerous heart rhythms. [8] | Poor kidney function is a listed cause. [8] The NHS says older people should not take potassium supplements unless advised by a doctor. [4] | Before any potassium supplement, especially with kidney disease or blood pressure medicines |
| Selenium | MedlinePlus lists hair loss, nail problems, nausea, irritability, fatigue and mild nerve damage (selenosis). [9] The NHS says the mildest form can lead to loss of hair and nails. [4] | Not described in the sources we read | If hair, nail or nerve symptoms appear |
| Iodine | The NHS says high doses for long periods could change how the thyroid works. [10] MedlinePlus says very high intake can reduce thyroid function. [11] | People on anti-thyroid medicines: taking high doses of iodine with them can cause hypothyroidism. [11] | Any thyroid condition or thyroid medicine |
| Copper | The NHS lists stomach pain, sickness and diarrhoea, and damage to the liver and kidneys if taken for a long time. [4] | Not described in the sources we read | Before long-term use |
| Phosphorus | The NHS says high doses for a short time can cause diarrhoea or stomach pain. [4] | Not described on the page we read; see Minerals, Supplements and Kidney Disease | Before supplements |
| Manganese | The NHS says long periods of high doses might cause muscle pain and nerve damage. [4] | Not described in the sources we read | Before supplements |
Limits of this table
- It shows reactions linked to high amounts. Normal amounts from food rarely cause these effects.
- It is not a list of every possible reaction. Allergic reactions and effects of mixed products are not covered.
- We could not open the NIH Office of Dietary Supplements fact sheets, so we do not give US upper limits here. For how US, UK, EU and Canadian references compare, see Mineral Intake References Compared.
When to seek care promptly
Call 911 or Poison Help for a child who swallowed a supplement, and for anyone with severe or worsening symptoms after a large amount. Ask a clinician or pharmacist about any ongoing symptom, any kidney, liver or thyroid condition, pregnancy or breastfeeding, and interactions with medicines. See Medication Interactions, Minerals, Supplements and Kidney Disease and Side Effects, Allergic Reactions & Reporting.Frequently asked questions
Which mineral supplement most often causes stomach upset?
The sources list stomach pain, nausea or diarrhoea for calcium, magnesium, zinc, iron, potassium and phosphorus at high amounts. [2] [4] [7] Proper evidence not found for a ranking by frequency in the sources we read.
Does taking minerals with food prevent side effects?
The pages we read for this table do not say. Timing and food are covered in Taking Mineral Supplements With Food or on an Empty Stomach; ask a pharmacist about your product.
Can mineral side effects be serious?
Yes at high amounts. Examples in the sources include fatal iron doses in children, dangerous heart rhythms from high blood potassium, and copper deficiency from long-term excess zinc. [7] [8] [4]
Do I need to stop my supplement if I notice a reaction?
Talk to your clinician or pharmacist. Do not change a prescribed medicine on your own.
Where can I report a reaction?
See the Side Effects, Allergic Reactions & Reporting page linked above.
References
- MedlinePlus (US National Library of Medicine). Iron overdose. Review date 10/14/2025. Read 2026-10-23.
- NHS (UK). Vitamins and minerals: Calcium. Page last reviewed 3 August 2020. Read 2026-10-23.
- MedlinePlus (US National Library of Medicine). Calcium in diet. Review date 1/21/2025. Read 2026-10-23.
- NHS (UK). Vitamins and minerals: Others (chromium, copper, magnesium, manganese, molybdenum, phosphorus, potassium, selenium, salt, zinc). Page last reviewed 3 August 2020. Read 2026-10-23.
- MedlinePlus (US National Library of Medicine). Magnesium 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.
- NHS (UK). Vitamins and minerals: Iron. Page last reviewed 3 August 2020. Read 2026-10-23.
- MedlinePlus (US National Library of Medicine). Potassium in diet. Review date 4/30/2026. Read 2026-10-23.
- MedlinePlus (US National Library of Medicine). Selenium in diet. Review date 1/21/2025. Read 2026-10-23.
- NHS (UK). Vitamins and minerals: Iodine. Page last reviewed 3 August 2020. Read 2026-10-23.
- MedlinePlus (US National Library of Medicine). Iodine in diet. Review date 1/21/2025. Read 2026-10-23.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.