Calcium and Constipation
Could those calcium supplements be
One of your constipation triggers?

Can calcium and constipation be connected? You won't find the answer on a box of calcium fortified breakfast cereals.

There is one message that has been consistently hammered into our heads this past decade: calcium is good for the bones.

The food industry has quickly followed suit. Calcium has been added to milk, fruit juices, cereals and more. It is liberally taken as supplement by people after a certain age to lower the risk of osteoporosis.

As we will see in this article, there is such thing as "calcium constipation". It can be explained by the way calcium acts on our body. We will see that even though the incidence is low, constipation is one side effect of calcium supplementation.

Finally, we will discuss a few things you can do if you need to take those calcium supplement due to your health condition, but want to lower the risk of calcium and constipation.

The role of calcium

Calcium is the most abundant mineral found in the human body. 99% is stored in bones and teeth, with the 1% remaining in the blood and other bodily fluids.

Calcium is of utmost importance to multiple physiological processes at the cellular, endocrine and nervous level: hormone production and regulation, cell and nerve signaling, blood pressure regulation, blood clotting, etc.

When there is not enough calcium circulating in our blood, the body will use multiple levers to bring this back to balance: our intestinal absorption of calcium will be increased, calcium elimination through the kidneys will be decreased.

Ultimately though, if we do not have enough calcium after those gut and kidney corrections, the body will start to pump calcium out of our bones and teeth (our reserves). Not good at all.

Certain people in certain age groups are more exposed to this problem - the elderly in particular, or women after menopause.

Even for children, adequate calcium absorption is necessary to ensure proper bone health later in their life, although exercise seems to be an even more critical factor(1). Carbonated drinks are to be avoided, since they are overly acidic and require lots of calcium (a base) to buffer the acidic load.

A diet rich in calcium from vegetables and fruits is essential. When calcium comes from natural foods, it comes packaged with a mix of other essential nutrients that are necessary for the proper absorption of calcium (vitamin D for instance) - they all work synergistically.

To be on the safe side, at-risk people of a certain age are told to use calcium supplements. If you take those supplements and you suspect a calcium and constipation connection, please read-on.

What about dairies as a source of calcium?

There has been so much hype and marketing behind dairy products and calcium that it is hard to see through the clutter. Especially for our children, there seems to be an obsession with milk and dairy consumption.

I will just quote from this comprehensive review article published by the American Academy of Pediatrics(2): "Scant evidence supports nutrition guidelines focused specifically on increasing milk or other dairy product intake for promoting child and adolescent bone mineralization".

The issue with dairies is not their calcium content. They are rich in calcium, no doubt about that. The issue is around bio-availability of said calcium, our ability to break it down and absorb it. Our body may not be able to optimally process it.

To me, sticking to a diet rich in plant sources makes more sense, and better reflect our human evolution. Man obviously needed calcium way before the advent of milk-producing domesticated animals.

What is the incidence of "calcium constipation"?

Based on a 5-year study done on 1460 elderly women taking calcium supplements(3), constipation was one of the main adverse event reported.

The occurrence of calcium and constipation among this sample was 13.4%, not much higher than in the placebo group (9.1%). The difference is nonetheless notable - about 4.3% of the constipation cases were due to calcium supplementation.

When you have been struggling for years with constipation trying to find a possible cause, nothing is negligible. Nothing should be swept under the rug. Even though the probability is low, the risk of calcium and constipation is still real.

Why does too much calcium causes constipation?

Reason 1: dehydration through the kidneys

The kidneys have a complex task to do. Among other things, they regulate the levels of electrolytes in our body: sodium, potassium, calcium, magnesium and more.

Through the retention or excretion of sodium, the kidneys control our level of hydration, how much water is being kept by our body.

Remember this simple rule: Water follows sodium.

When the kidneys want to reduce the level of water in our body (because we absorbed a large amount for instance), they evacuate sodium through our urine. Water follows the salt, having a net dehydrating effect. When the kidneys want to retain water (because it is hot outside and we are getting dehydrated), they will retain sodium in our blood. The water will say in.

What does this have to do with calcium then?

Sodium competes with calcium for reabsorption in the kidneys. If you have lots of calcium circulating in your blood, it will impair reabsorption of salt into your blood by the kidneys. Salt, not being able to be reabsorbed in your blood after filtration, will leave the body. Water will follow.

Less water available to your bodily functions. Rings a bell? This means the risk of constipation is increased.

To confirm this point, two of the documented side effects of calcium citrate are: - dry mouth or increased thirst - increased urination.

Reason 2: lack of tonicity of gastrointestinal muscles 
A high level of calcium in your blood has a depressive effect on your nervous system, which results in the lack of tonicity of the smooth muscles of your gastrointestinal tract.

As a result, the colon may move slower. Food residues stay longer in the "dehydrating machine" that the colon is. This leads to constipation.

A note on vitamin D

Vitamin D is an essential vitamin, helpful for calcium absorption, but also for a healthy immune system and other major functions.

Vitamin D is not directly implicated in constipation. However, it enhances absorption of calcium by your intestine. Therefore, if you take both calcium and vitamin D supplements, vitamin D will increase your level of calcium in circulation. Indirectly, it may therefore contribute to constipation by making calcium more available to your body.

If you do have to take calcium supplementation though, it makes sense to take it with vitamin D, to ensure you make the most out of those supplement pills.

If you need to take calcium supplements

Certain people, women undergoing menopause for instance, will be asked by their doctor to take calcium supplements to lower the risk of osteoporosis. What to do then to avoid the calcium and constipation issue?

1- Ensure calcium is indeed implicated in your constipation. Use the withdrawal and re-challenge method. Stop for a while. Has your constipation improved? Then re-introduce calcium supplements. Has your constipation worsened? If yes, you know for sure calcium and constipation are related. Once you know for sure, you can move to the next step.

2- Not all calcium supplements are made equal. The following forms are more readily absorbed: citrate(4), glutamate, and aspartate. Calcium citrate in particular seems to be better tolerated by the elderly. Those forms should be favored over the less bioavailable forms: phosphate, sulfate and carbonate (the most common one). Calcium carbonate is very cheap but should be avoided to limit the risk of calcium and constipation.

Some points worth noting:

  • The more bioavailable forms of calcium (citrate in particular) are more expensive;
  • A pill of calcium citrate contains half of the elemental calcium of the same pill of calcium carbonate (thus making citrate even more expensive compared to carbonate);
  • Contrary to what most of the website seem to portray, I have seen cases of calcium and constipation provoked by calcium citrate. Calcium carbonate is not the only culprit.

3- Get more calcium from food sources. It is better tolerated by the body. According to Whole Foods(5), the following foods are rich in calcium. You can find the calcium equivalence for those food on the internet. One cup of kale for instance contains 100mg of calcium. Try to see if you can reduce your supplementation based on the extra you are taking as food (1 cup of kale added to your diet, as an example, could mean 100mg less to take as a supplement).

Calcium Content Food
Excellent Spinach, turnip greens, mustard greens and collard greens.
Very good Blackstrap molasses, Swiss chard, yogurt, kale, mozzarella cheese, cow's milk, and goat's milk. Basil, thyme, dill seed, cinnamon, and peppermint leaves.
Good Romaine lettuce, celery, broccoli, sesame seeds, fennel, cabbage, summer squash, green beans, garlic, tofu, Brussel sprouts, oranges, asparagus and crimini mushrooms. Oregano, rosemary, parsley, kombu, and kelp.

4- Spread the dose throughout the day. If you need to take 1200mg per day for instance, try to take it in 4 doses of 300mg. It will be absorbed much better this way. Take it with meals, and away from other medications if possible.

5- Find the dose that is right for you. Maybe 1200mg total per day constipates you, but 800mg for instance, spread throughout the day is much better tolerated. Once you get a better feel for what threshold makes calcium and constipation worse, discuss this dose with your health practitioner.


Calcium is essential for life. It is involved in numerous physiological processes. Because it has been hammered into our brains so many times, we also know that it helps prevent osteoporosis. Your doctor may have prescribed some calcium supplement based on your age, gender and osteoporosis risk level.

We have seen in this article that even though the probability is low, calcium and constipation may be interrelated.

If you know this is the case, you will need to find the form and dose that is right for you. Life is all about compromises. You should not stop taking calcium if it is recommended by your doctor. But you should not live with constipation either. You should try different forms of calcium, and if possible increase food sources which are much better tolerated.

Where is the sweet spot for you? What calcium regimen can severe the calcium and constipation connection? That is for you to experiment.

(1) Lloyd T, Petit MA, Lin HM, Beck TJ. "Lifestyle factors and the development of bone mass and bone strength in young women". J Pediatr 2004;144:776-782.

(2) Lanou AJ, Berkow SE, Barnard ND. "Calcium, dairy products, and bone health in children and young adults: a reevaluation of the evidence". Pediatrics 2005;115:736-743.

(3) Prince RL, Devine A, Dhaliwal SS, Dick IM. "Effects of calcium supplementation on clinical fracture and bone structure: results of a 5-year, double-blind, placebo-controlled trial in elderly women". Arch Intern Med. 2006 Apr 24;166(8):869-75. PubMed PMID: 16636212.

(4) Harvey JA, Zobitz MM, Pak CY. "Dose dependency of calcium absorption: a comparison of calcium carbonate and calcium citrate". J Bone Miner Res 1988;3:253-258.

(5) Whole foods Calcium information page at:

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