Too Much Calcium: Hypercalcemia, Milk-Alkali Syndrome and Upper Limits
What high blood calcium (hypercalcemia) is, what causes it, how milk-alkali syndrome happens, and the official upper limits from the UK, EU, US and Canada.
Content last updated . This page has not been medically reviewed.
Urgent first
Very high calcium in the blood can cause nausea or vomiting, strong thirst, constipation, muscle weakness and confusion. [1] Severe cases that cause symptoms can need a hospital stay, where fluids through a vein are the most important treatment. [1] If someone is very confused or extremely unwell, call 911 (US) or your local emergency number. If a child or adult has swallowed a large amount of a calcium or vitamin D product by accident, call Poison Help at 1-800-222-1222 (US; other countries are on Poison Help by Country).What hypercalcemia is
Hypercalcemia means there is too much calcium in the blood. [1] It is a blood-test finding with medical causes, not the same thing as eating a lot of calcium-rich food. Most people with it have no symptoms, and it is often found on routine blood tests. [1]What causes it
| Cause | What the source says |
|---|---|
| Overactive parathyroid glands (hyperparathyroidism) | The most common cause of a high blood calcium level is excess parathyroid hormone (PTH). [1] The NHS describes the same condition. [2] |
| Some cancers | Certain cancers, such as lung and breast cancer, or cancer that has spread. [1] |
| Too much vitamin D | MedlinePlus lists too much vitamin D in the blood; the NHS says long-term excess vitamin D supplements can cause calcium to build up in the body. [1][3] |
| Too much calcium plus alkali (milk-alkali syndrome) | See the next section. [1][4] |
| Medicines | Thiazide diuretics (water pills) and lithium are listed. [1] A 2021 review explains that thiazides and lithium act through the parathyroid and kidney, and that vitamin D supplements raise calcium absorption. [5] |
| Other conditions | Kidney disease, overactive thyroid, being bedridden for a long time, some infections and inherited conditions. [1] |
Dehydration can also raise blood calcium. [1] Anyone with a high result needs a clinician to find the cause, and the tests MedlinePlus lists include blood calcium, PTH and vitamin D levels and urine calcium. [1]
Milk-alkali syndrome
A Mayo Clinic Proceedings review defines it as high blood calcium, some degree of kidney failure and metabolic alkalosis (blood that is too alkaline) from large amounts of calcium and absorbable alkali. [4] It was first seen when ulcers were treated with milk and alkali; it became rare, then returned with wide use of calcium carbonate, mostly for osteoporosis prevention. [4] MedlinePlus says it most often occurs with more than 2,000 mg a day of calcium supplements (its page says "calcium bicarbonate") taken with high doses of vitamin D. [1] Treatment is supportive: fluids and stopping the products responsible, under medical care. [4]Proper evidence not found: a single amount of ordinary supplement calcium that causes hypercalcemia in healthy people. We searched MedlinePlus, the NHS and PubMed reviews; they describe causes and cases, not a threshold.
Official upper limits
An upper limit (UL) is a ceiling for long-term daily intake, not a goal. The figures below are mg per day of calcium.| Source and year | Population | Upper limit |
|---|---|---|
| NHS (UK), 2020 | Adults | More than 1,500 mg a day could cause stomach pain and diarrhoea; 1,500 mg or less is unlikely to cause harm [6] |
| EFSA (EU), 2025 overview of 2012 opinion | Adults, including pregnancy and breastfeeding | 2,500, from diet and supplements together [7][8] |
| EFSA (EU), same | Infants, children, adolescents | No UL set: not enough data, though no risk was identified at the highest current intakes [7][8] |
| Health Canada (US/Canada DRIs, 2011) | Ages 1 to 8; adults 19 to 50, including pregnancy and breastfeeding at those ages | 2,500 [9] |
| Health Canada, same | Ages 9 to 18, including pregnant or breastfeeding teens | 3,000 [9] |
| Health Canada, same | Adults 51 and older | 2,000 [9] |
| Health Canada, same | Infants 0 to 6 months; 7 to 12 months | 1,000; 1,500 [9] |
The bodies differ, and the Health Canada page does not say whether its figure counts food, water and supplements together. EFSA's limit is based on trials in which total intakes of 2,500 mg from diet and supplements were tolerated, and it found no established link between long-term calcium intake and kidney stones, cardiovascular disease or prostate cancer. [8] MedlinePlus, by contrast, says long-term higher intakes raise kidney-stone risk in some people. [10] See Calcium Supplements, Heart Disease and Kidney Stones.
Quality note
Products vary and labels can be wrong; see Quality Testing and Certifications. For roles, food sources and intake levels, see Calcium.Frequently asked questions
Can you get too much calcium from food alone?
The sources we read focus on supplements, antacids, vitamin D and medical causes of high blood calcium, not ordinary food. [1][6] Proper evidence not found for hypercalcemia from food alone in healthy people.
What is the calcium upper limit for adults?
It depends on the body and year: 1,500 mg a day is the NHS "unlikely to cause harm" figure, 2,500 mg is EFSA's adult limit, and Health Canada lists 2,500 mg for ages 19 to 50 and 2,000 mg from 51. [6][7][9]
What are symptoms of too much calcium?
Nausea, vomiting, poor appetite, constipation, thirst, frequent urination, weakness and confusion, though many people have none. [1] These symptoms have many causes, so a blood test and a clinician are needed.
What is milk-alkali syndrome?
High blood calcium, kidney problems and alkalosis caused by large amounts of calcium with absorbable alkali, such as calcium carbonate antacids. [4]
Do antacids count as calcium?
Calcium carbonate antacids contain calcium; MedlinePlus says each chew or pill usually provides 200 to 400 mg, so check the label. [10]
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.
Who should ask a clinician before using calcium or vitamin D supplements
- People with kidney disease, kidney stones, or any parathyroid condition. The NHS says not to change the diet to lower calcium unless a specialist advises it. [2] See Minerals, Supplements and Kidney Disease.
- People taking thiazide diuretics or lithium, or other prescribed medicines. Ask a pharmacist; see Medication Interactions.
- Anyone combining calcium, antacids and vitamin D, since several products can contain calcium. MedlinePlus advises talking to a provider about the correct amounts. [1]
- Pregnancy, breastfeeding, children and older adults, and before surgery: tell the care team about every supplement.
References
- MedlinePlus (US National Library of Medicine), Hypercalcemia. Review date 25 January 2026. Read 2026-10-23.
- NHS (UK), Hyperparathyroidism. Page last reviewed 12 June 2025. Read 2026-10-23.
- NHS (UK), Vitamins and minerals: Vitamin D. Page last reviewed 3 August 2020. Read 2026-10-23.
- Medarov BI, Milk-alkali syndrome. Mayo Clin Proc 2009;84(3):261-267 (review; PubMed abstract). Read 2026-10-23.
- Lecoq AL et al., Drug-related hypercalcemia. Endocrinol Metab Clin North Am 2021;50(4):743-752 (review; PubMed abstract). Read 2026-10-23.
- NHS (UK), Vitamins and minerals: Calcium. Page last reviewed 3 August 2020. Read 2026-10-23.
- European Food Safety Authority, Overview on Tolerable Upper Intake Levels as derived by the SCF and the EFSA NDA Panel, version 1, August 2025, Table 1. Read 2026-10-23.
- EFSA NDA Panel, Scientific Opinion on the Tolerable Upper Intake Level of calcium. EFSA Journal 2012;10(7):2814 (PubMed abstract). Read 2026-10-23.
- Health Canada, Dietary reference intakes reference values for elements, Table 1. Calcium values published in 2011. Read 2026-10-23.
- MedlinePlus (US National Library of Medicine), Calcium in diet. Review date 21 January 2025. Read 2026-10-23.