Do Calcium Cause Diarrhea? Understanding the Side Effects

January 9, 2026 •

3 min read

According to the National Health Service, taking high doses of calcium—more than 1,500mg per day—could potentially lead to stomach pain and diarrhea. While calcium is vital for bone health and other bodily functions, an excessive intake, particularly from supplements, can disrupt your digestive system. Understanding the factors that contribute to this reaction is crucial for those who rely on supplementation.

Quick Summary

Excessive doses of calcium supplements can lead to digestive issues, including diarrhea. This occurs because the intestinal absorption capacity can be overwhelmed, leading to an osmotic effect. The specific form of calcium, like citrate versus carbonate, can also influence the risk of gastrointestinal side effects.

Key Points

High-Dose Supplements: Taking high doses of calcium supplements, particularly over 1,500mg daily, is the most common cause of diarrhea linked to calcium.
Osmotic Effect: Excess, unabsorbed calcium pulls water into the intestines, leading to loose stools and a type of diarrhea known as osmotic diarrhea.
Formulation Matters: Calcium carbonate is more often associated with constipation, while some individuals find calcium citrate can cause loose stools or diarrhea.
Divide and Conquer: Taking smaller, divided doses throughout the day can significantly reduce the risk of digestive issues by improving absorption.
Magnesium Balance: An imbalance with magnesium can influence digestive motility. Some find supplementing with magnesium can help counteract calcium's effects.
With Food or Without: Always take calcium carbonate with food to aid absorption. Calcium citrate can be taken with or without, but taking it with meals can still reduce the chance of side effects.

The Connection Between Calcium and Diarrhea

While dietary calcium is generally well-tolerated, high-dose supplementation is the primary cause of calcium-induced diarrhea. Consuming a large amount of a calcium supplement can overwhelm the small intestine's absorption capacity, leading to unabsorbed calcium. This excess calcium creates an osmotic effect, drawing water into the bowel and causing loose stools. Individuals with digestive sensitivities may be more susceptible.

Formulations Matter: Citrate vs. Carbonate

The type of calcium supplement impacts the potential for digestive distress. Calcium carbonate and calcium citrate are common forms with different absorption characteristics and side effects.

Calcium Carbonate: More likely to cause constipation, gas, and bloating. Some with loose stools might find it helpful due to its constipating effect. It has a higher percentage of elemental calcium and requires stomach acid, so it's taken with food.
Calcium Citrate: Generally better absorbed with fewer gastrointestinal issues like bloating or constipation. However, some may experience loose stools or diarrhea with this form. It can be taken with or without food as it is less dependent on stomach acid for absorption.

Additional Contributing Factors

Other factors can increase the likelihood of calcium-related diarrhea:

Vitamin D: High doses of Vitamin D, which boosts calcium absorption, can contribute to digestive effects.
Magnesium Balance: Calcium and magnesium compete for absorption. High calcium can hinder magnesium absorption, and magnesium has a natural laxative effect, so an imbalance might cause digestive issues.
Individual Sensitivity: Tolerance varies among individuals based on age, gut health, and other conditions.

Comparison of Calcium Supplement Side Effects


Feature	Calcium Carbonate	Calcium Citrate
Likelihood of Constipation	Higher	Lower
Likelihood of Diarrhea	Possible, especially at high doses	Possible for some individuals, particularly loose stools
Requires Stomach Acid for Absorption?	Yes, must be taken with food	No, can be taken with or without food
Elemental Calcium Content	Higher (approx. 40%)	Lower (approx. 21%)
Cost	Generally less expensive	Tends to be more expensive

Strategies to Prevent Calcium-Related Diarrhea

To manage digestive side effects from calcium supplements, consider these strategies:

Divide Doses: Split the daily dose into smaller amounts taken throughout the day to improve absorption and reduce unabsorbed calcium.
Take with Meals: Consuming supplements with food can slow absorption and decrease gastrointestinal upset, especially important for calcium carbonate.
Switch Formulations: If one form causes issues, try the other.
Optimize Magnesium: Ensure adequate magnesium intake, as it interacts with calcium and influences digestion.
Stay Hydrated: Hydration is crucial, especially when experiencing diarrhea.
Reduce Dosage Temporarily: If symptoms are severe, briefly lower the dose and gradually increase it as tolerated.

Conclusion

Dietary calcium rarely causes diarrhea; the risk is primarily from high-dose supplements. Both calcium carbonate and calcium citrate can cause digestive issues, but they affect individuals differently. Managing this involves selecting the right formulation, splitting doses, and taking supplements with food. If digestive problems persist, consult a healthcare professional. For more information, visit the National Institutes of Health Office of Dietary Supplements website https://ods.od.nih.gov/factsheets/Calcium-HealthProfessional/.

Note: This information is for general knowledge and is not a substitute for professional medical advice. Always consult a healthcare provider before starting any new supplement.

Disclaimer

The information in this article is for informational purposes only and does not constitute medical advice. Consult a healthcare professional for diagnosis and treatment of any medical condition.

Frequently Asked Questions

Yes, taking excessively high doses of calcium supplements, often more than 1,500mg per day, can cause digestive upset, including diarrhea and stomach pain.

While calcium carbonate is more commonly associated with constipation, calcium citrate can cause loose stools or diarrhea in some individuals. The best option depends on your individual tolerance.

To prevent diarrhea, try splitting your daily dose into smaller, multiple doses, and take them with meals. You can also try switching to a different calcium formulation, such as calcium citrate if carbonate is causing issues.

Too much calcium can overwhelm the intestine's capacity for absorption. This unabsorbed calcium then draws water into the colon, leading to an osmotic effect that results in diarrhea.

No, it is highly unlikely to get too much calcium from diet alone. The body naturally regulates calcium absorption from food, so most cases of calcium-induced diarrhea are from high supplemental intake.

Magnesium has a natural laxative effect, so ensuring a good balance with your calcium intake can help maintain digestive regularity. Some people find taking a combined supplement or staggering their doses helps.

For most adults, the recommended daily allowance is 1,000-1,200mg, with an upper limit of 2,000-2,500mg depending on age. It is important to consider both dietary and supplemental sources and not exceed the tolerable upper intake levels.