Minerals and Stomach Acid: Antacids, Acid Reducers (PPIs) and Absorption of Calcium, Iron, Magnesium and B12
What studies and health services say about antacids and acid-reducing medicines (PPIs) and the absorption of calcium, iron, magnesium and B12. Never a reason to stop a medicine.
Content last updated . This page has not been medically reviewed.
Quick answer
Stomach acid helps with some nutrient absorption, so medicines that lower it have been studied for effects on calcium, iron, magnesium and vitamin B12. The research is mostly observational, the results are mixed, and for some minerals (calcium) the answer depends on the supplement form and whether it is taken with food. This page is not advice to stop or change a medicine. MedlinePlus says not to stop taking these medicines without talking with your provider first. [1] A pharmacist or prescriber can review your medicines and supplements together. See Medication Interactions.
Two different kinds of medicine
- Antacids neutralize acid already in the stomach. The NHS lists their ingredients as including aluminium hydroxide, magnesium carbonate, magnesium trisilicate, magnesium hydroxide, calcium carbonate and sodium bicarbonate. [2] So some antacids are also sources of calcium or magnesium.
- Proton pump inhibitors (PPIs) are medicines that work by reducing the amount of stomach acid made by the stomach lining. [1]
Evidence labels used below: mixed, limited, observational only (association, cannot prove cause) and Proper evidence not found.
What research found
| Nutrient | What the source found | Strength |
|---|---|---|
| Calcium (acid suppression) | In a small 1984 study a large dose of cimetidine, which markedly reduced stomach acid, had no effect on calcium absorption in normal subjects. [3] | Limited: small, old, short-term |
| Calcium carbonate with no acid | A 1985 study found calcium absorption from carbonate was impaired in achlorhydria (no stomach acid) under fasting conditions. [4] Taken with a normal breakfast, absorption in those patients was completely normal. [4] | Limited: 11 patients |
| Calcium and fractures | A meta-analysis found a modest association between PPI use and hip and vertebral fractures. [5] The authors said observational studies cannot show whether it is causal. [5] | Observational only |
| Iron | A large case-control study found that two or more years of acid-inhibitor use was associated with a higher risk of iron deficiency. [6] | Observational only |
| Magnesium | A 2014 meta-analysis said PPI use may increase the risk of low magnesium, but heterogeneity prevented a definitive conclusion. [7] A 2019 update said the association remained unclear. [8] | Mixed |
| Vitamin B12 | A 2023 meta-analysis found B12 deficiency slightly more common in PPI users, with significant heterogeneity. [9] The NHS lists very low vitamin B12 as a possible serious side effect, more likely with use for a year or more. [10] | Mixed |
Calcium: form and food matter
MedlinePlus says calcium carbonate is absorbed better if taken with food, and calcium citrate is taken up well on a full or empty stomach. [11] That fits the 1985 finding above. For the head-to-head see Calcium Carbonate vs Calcium Citrate and Taking Mineral Supplements With Food or on an Empty Stomach.Bones and B12: what health services say
MedlinePlus says to ask your provider about possible concerns with long-term PPI use, such as infections and bone fractures. [1] The NHS lists weakened bones among rare serious side effects. [10] Vitamin B12 is covered in Vitamin B12 and Vitamin B12 Deficiency.What we could not verify
Proper evidence not found: a trial showing that taking a mineral or B12 supplement prevents harm in PPI users. We searched PubMed for PPI and calcium, iron, magnesium and B12 studies and read meta-analyses and one large case-control study. We could not open the FDA drug-safety communication on PPIs and low magnesium (the page returned an error), so we do not describe FDA labeling.Who should talk to a clinician
Older adults, people with kidney disease, people taking diuretics or several medicines, and anyone who has used acid reducers for a year or more are the groups where nutrient questions matter most. See Minerals for Older Adults. Pregnant or breastfeeding people should ask before taking acid reducers; MedlinePlus says to talk to your provider. [1]Frequently asked questions
Do antacids and PPIs block calcium absorption?
Studies are mixed. Acid suppression did not change calcium absorption in normal subjects in a small 1984 study. [3] Calcium carbonate absorption was poor in people with no stomach acid when fasting, but normal with a meal. [4]
Do PPIs cause low iron?
A large study found an association with iron deficiency after two or more years of use, but association is not proof of cause. [6]
Do PPIs lower magnesium?
Meta-analyses say it is possible but unclear because of heterogeneity. [7] [8]
Should I take a B12 supplement if I use a PPI?
Ask your clinician. The NHS lists very low B12 as a possible serious side effect of omeprazole. [10] Do not stop the medicine yourself. [1]
Are calcium antacids a good calcium source?
MedlinePlus notes that calcium carbonate is the form found in over-the-counter antacid products. [11] Whether that counts toward your needs is a question for a pharmacist, and long-term antacid use is not recommended by the NHS. [2]
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.
Antacids as a source of minerals, and other cautions
- The NHS says antacids can affect how well other medicines work, so other medicines should not be taken within 2 to 4 hours of an antacid. [2] Ask a pharmacist about timing with your own medicines and supplements.
- The NHS says long-term antacid use is not recommended and that people with liver disease, kidney disease or heart failure should ask first, because some antacids may not be safe. [2]
- Magnesium is a concern in kidney disease: MedlinePlus says side effects of high magnesium are not common except in people with significantly reduced kidney function, and excess most often occurs with supplements or magnesium-containing laxatives. [12] A published case report described fatal hypermagnesemia in a woman with chronic constipation treated with magnesium-containing laxatives. [13] That is one case, not a rate.
References
- MedlinePlus (US National Library of Medicine). Proton pump inhibitors. Review date 4/21/2025. Read 2026-10-23.
- NHS (UK). Antacids. Page last reviewed 24 March 2023. Read 2026-10-23.
- Bo-Linn GW and others. An evaluation of the importance of gastric acid secretion in the absorption of dietary calcium. Journal of Clinical Investigation, 1984. Read 2026-10-23.
- Recker RR. Calcium absorption and achlorhydria. New England Journal of Medicine, 1985. Read 2026-10-23.
- Proton pump inhibitors and risk of fracture: a systematic review and meta-analysis of observational studies. American Journal of Gastroenterology, 2011. Read 2026-10-23.
- Lam JR and others. Proton pump inhibitor and histamine-2 receptor antagonist use and iron deficiency. Gastroenterology, 2017. Read 2026-10-23.
- Park CH and others. The association between the use of proton pump inhibitors and the risk of hypomagnesemia: a systematic review and meta-analysis. PLoS One, 2014. Read 2026-10-23.
- Liao S and others. Does the use of proton pump inhibitors increase the risk of hypomagnesemia? An updated systematic review and meta-analysis. Medicine (Baltimore), 2019. Read 2026-10-23.
- Choudhury A and others. Vitamin B12 deficiency and use of proton pump inhibitors: a systematic review and meta-analysis. Expert Review of Gastroenterology and Hepatology, 2023. Read 2026-10-23.
- NHS (UK). Omeprazole (medicine page on proton pump inhibitor side effects). 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). Magnesium in diet. Review date 1/21/2025. Read 2026-10-23.
- Bokhari SR and others. Fatal hypermagnesemia due to laxative use. American Journal of the Medical Sciences, 2018 (case report). 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.