Do Calcium and Magnesium Supplements Cause Constipation? Understanding the Digestive Impact

October 13, 2025 •

4 min read

While both calcium and magnesium are essential minerals for bodily function, they have very different effects on digestive health, with one commonly associated with causing constipation and the other with relieving it. The specific type and balance of your supplements are key factors in determining whether calcium and magnesium supplements cause constipation.

Quick Summary

Calcium supplements, particularly calcium carbonate, may slow intestinal movement and cause constipation in some individuals. In contrast, magnesium acts as an osmotic laxative, drawing water into the intestines to promote bowel movements. Understanding the distinct actions of these minerals and their interactions is crucial for maintaining digestive comfort during supplementation.

Key Points

Calcium can cause constipation: Some calcium supplements, especially calcium carbonate, are known to cause constipation by slowing intestinal movement and reducing fluid secretion.
Magnesium acts as a laxative: Magnesium draws water into the intestines and relaxes intestinal muscles, which helps relieve constipation.
The type of supplement matters: Calcium carbonate is more constipating than calcium citrate, while magnesium oxide is a strong laxative due to its low absorption rate.
Balance is key for digestion: Taking a balanced calcium-magnesium supplement, or spacing doses, can help counteract calcium's constipating effects.
Preventive measures are effective: Staying hydrated, eating enough fiber, and choosing less constipating supplement forms can prevent or manage digestive issues.
Consult a healthcare provider: It is important to talk to a doctor about the right supplement form and dosage, especially if you have other health conditions or take medication.

The Distinct Roles of Calcium and Magnesium

Calcium and magnesium are two of the most vital minerals in the human body, playing synergistic roles in hundreds of physiological processes. Calcium is essential for building and maintaining strong bones, nerve signaling, and muscle contraction. On the other hand, magnesium is critical for nerve and muscle relaxation, energy production, and regulating blood sugar. The balance between these two minerals is crucial for maintaining overall health, but their unique effects on the digestive system are often misunderstood.

The Link Between Calcium Supplements and Constipation

For many individuals, taking calcium supplements can lead to gastrointestinal side effects, most notably constipation. This is particularly true for certain types of calcium. Research suggests the following mechanisms explain this effect:

Slows intestinal motility: Calcium can slow down the rhythmic contractions of intestinal muscles (peristalsis) that move food and waste through the digestive tract.
Reduces fluid secretion: It may also decrease the amount of fluid secreted into the gut, leading to harder, drier stools that are more difficult to pass.
Type matters: The form of calcium is a significant factor. Calcium carbonate, which is commonly found in supplements and antacids, is an alkaline compound that can neutralize stomach acid. This can interfere with the breakdown of food and absorption of minerals, contributing to constipation.

Magnesium's Role: A Natural Laxative

Unlike calcium, magnesium is well-known for its laxative effects, especially when taken in certain forms. This is why magnesium-based products like milk of magnesia are used as over-the-counter remedies for constipation. The mechanism behind magnesium's effect is as follows:

Osmotic effect: When taken orally, magnesium draws water from the body into the intestinal lumen. This increases the water content in the stool, softening it and making it easier to pass.
Muscle relaxation: Magnesium helps relax the muscles throughout the body, including the intestinal walls. This relaxation can help facilitate bowel movements.
Bioavailability variations: Different forms of magnesium have different absorption rates. Magnesium oxide, for instance, has low bioavailability, meaning a large portion remains in the intestines to exert its laxative effect. Highly bioavailable forms like magnesium glycinate are absorbed more readily and are less likely to cause a laxative effect.

Achieving Balance: When Taken Together

For individuals supplementing with both minerals, the effect on digestion often depends on their ratio and the forms used. A proper balance can help mitigate the constipating effects of calcium. Some combination supplements are formulated with a specific calcium-to-magnesium ratio (such as 2:1) to promote both bone health and digestive regularity. However, taking a large dose of calcium can interfere with the absorption of magnesium, so spacing out intake may be beneficial.

How to Prevent Supplement-Related Constipation

If you experience constipation while taking mineral supplements, consider the following strategies:

Hydrate adequately: Drink plenty of water throughout the day. Water is essential for softening stool and improving digestive transit.
Increase dietary fiber: Incorporate high-fiber foods like fruits, vegetables, whole grains, nuts, seeds, and beans into your diet. Fiber adds bulk to stool, which helps stimulate bowel movements.
Choose the right supplement form: If calcium carbonate causes issues, try switching to a gentler form like calcium citrate.
Time your dosage: Spreading your calcium intake into smaller doses throughout the day can improve tolerability. Many people take magnesium in the evening, which may aid in overnight muscle relaxation and morning bowel movements.
Balance minerals: Opt for a combined calcium-magnesium supplement or adjust your intake of each to ensure a proper balance.
Stay active: Regular physical activity helps stimulate the digestive tract and can significantly improve bowel function.

Side-by-Side Comparison of Calcium and Magnesium Effects


Aspect	Calcium Supplements	Magnesium Supplements
Effect on bowel movements	Can cause constipation, especially in high doses.	Acts as a natural osmotic laxative, relieving constipation.
Mechanism	May slow intestinal motility and decrease fluid in the gut.	Draws water into the intestines to soften stool and relaxes intestinal muscles.
Associated forms	Calcium carbonate is most associated with constipation.	Magnesium oxide and citrate are often used for their laxative effect.
Digestive side effects	Constipation, gas, bloating, and abdominal pain are common.	Diarrhea, stomach cramps, and nausea can occur with high doses.
Role in bone health	Essential for bone density and strength.	Necessary for proper calcium absorption and utilization.

Food Sources for Calcium and Magnesium

Reducing reliance on high-dose supplements can help manage digestive symptoms. Here are some excellent dietary sources for both minerals:

Calcium-Rich Foods:

Dairy products like milk, cheese, and yogurt
Leafy green vegetables such as kale and spinach
Fortified foods like cereals and orange juice
Canned fish with bones, such as sardines and pilchards

Magnesium-Rich Foods:

Nuts and seeds, including pumpkin and almonds
Legumes such as beans and lentils
Whole grains
Leafy greens, including spinach and kale
Dark chocolate

Conclusion

While calcium supplements, particularly calcium carbonate, can indeed contribute to constipation, magnesium has the opposite effect and is often used as a mild laxative. The outcome depends heavily on the specific forms of the minerals, the dosage, and the balance between them. By staying hydrated, increasing dietary fiber, and potentially adjusting the type and timing of your supplements, it is possible to manage or prevent the digestive discomfort associated with supplementing your nutrition. Always consult a healthcare professional before making significant changes to your supplement regimen, especially if you have pre-existing health conditions or are taking other medications.

A note on supplement safety

Always ensure your supplements are from a reputable source. Organizations like the United States Pharmacopeial Convention (USP) independently test and verify supplements for quality and content.

Frequently Asked Questions

Calcium citrate and calcium lactate are generally considered less likely to cause constipation compared to calcium carbonate, which is the most common and potentially most constipating form.

For constipation relief, magnesium oxide or magnesium citrate are often recommended because they have a stronger osmotic effect, drawing more water into the bowel. Taking it with a full glass of water, often at night, can help produce a morning bowel movement.

While it is generally safe to take them together, taking high doses of calcium and magnesium simultaneously can interfere with absorption. Many experts recommend spacing out the doses throughout the day or taking them with meals.

Some healthcare professionals and companies suggest a calcium-to-magnesium ratio of 2:1 or 3:1 to help balance the minerals' effects. The ideal dosage depends on individual needs, diet, and supplement forms, so a doctor's advice is best.

Increasing your intake of high-fiber foods such as fruits, vegetables, and whole grains is crucial. Additionally, ensuring you are drinking plenty of fluids throughout the day can significantly help soften stools.

Yes, other supplements, such as iron, can also cause constipation. If you take a multivitamin, check the iron and calcium content to see if they might be contributing to your digestive issues.

Yes, people with kidney disease should use magnesium supplements with caution and only under a doctor's supervision. Impaired kidney function can lead to a buildup of magnesium in the blood (hypermagnesemia), which can be dangerous.