If you have osteoporosis, your doctor has likely told you about calcium supplements. Your bones depend on calcium, and if you aren't getting enough from your diet, supplements are essential. Calcium supplements are also essential after parathyroid surgery, and most of my parathyroid patients want guidance on which one to buy. At this point I’ve treated thousands of patients on pretty much every type of calcium supplement, and I’ve even tried a few myself.
Pure calcium is a metal, but that is not what you find in supplements. Calcium, in nature and in the supplement aisle, exists primarily bound to something else in a compound. The most common is called calcium carbonate. This is the one you find in eggshells and limestone. In supplements, calcium carbonate is the cheapest and most widely available form of calcium; it’s the main ingredient in Tums, Caltrate, Os-Cal, and “oyster shell” calcium.
Calcium citrate is another common compound used in supplements. It is a little more expensive, and isn’t quite as common as calcium carbonate, but you can get it in the drugstore as the main ingredient in Citracal Maximum and its generic versions.
If you start looking, you will find other forms of calcium: calcium gluconate, calcium lactate, and tricalcium phosphate are just a few. Again, calcium is never floating around by itself; there is no supplement with pure elemental calcium in it. Calcium carbonate and calcium citrate are the most common forms, and are the ones we have the most research on.
This contains calcium made by algae, which is mostly calcium carbonate. The big difference with AlgaeCal is that it also contains many other minerals and micronutrients present in algae, which many other supplements lack. Some of these are known to aid in calcium metabolism, though it isn’t completely clear that you need to take supplements for them (you probably get enough from your diet).
Calcium supplements often affect the gastrointestinal tract. All of the types can cause intestinal upset, but calcium carbonate is particularly notorious for causing constipation and bloating. Not everyone will get constipated when taking it, but a significant number will. They will have hard stools, bloating, flatulence, and abdominal discomfort. When this happens, many people quite reasonably decide to stop taking calcium supplements. Simply trying a different brand at the drugstore may not help, since there is a good chance it contains calcium carbonate as well.
Other forms of calcium tend to cause constipation as well, though not as often as calcium carbonate. Calcium citrate tends to perform the best; there are fewer gastrointestinal side effects compared to other calcium supplements. Interestingly, some patients taking high doses of Citracal Maximum experience not constipation but loose stools.
Often overlooked in online summaries of calcium supplements (and in doctors’ recommendations), palatability is probably the most important consideration for many patients. Supplements vary widely in this regard.
The most common option is a large, hard tablet. Citracal Maximum and Oscal are good examples. The pills are always large, because calcium takes up a lot of space. This is why your multivitamin only has a tiny amount of calcium – the pill can only fit a small amount in addition to all of the other vitamins and minerals. Some calcium pills are massive; Citracal Maximum is a “horse pill” that can be difficult to get down without choking, especially for women. You can break it in half, but when you do that you end up with sharp edges, which can make it even more unpleasant. You can also crush it and mix it in a drink or apple sauce, but that might not hide the taste.
For those with difficulty swallowing large pills, there are chewable and gummi calcium supplements. But they may not be any easier to tolerate. I’ve tried chewable calcium tabs that were so unbearably chalky that I had trouble ingesting just one tab. There was no way I could get down the three per serving that the bottle recommended. Others are sickeningly sweet, covered in sugar.
Of course this is subjective. Some people can’t stand vanilla-orange flavoring, but others will prefer it. I can’t swallow large pills easily, but many of my patients have no issues with downing huge pills. The most palatable calcium pill will not be the same for everyone, and many people will need to experiment with multiple types to find the right one.
We have fairly good studies comparing the intestinal absorption of calcium carbonate and calcium citrate, and it is clear that calcium citrate is more readily absorbed. Calcium carbonate requires stomach acid to break down prior to absorption, so it needs to be taken with food to maximize its absorption. And someone on medications that decrease stomach acid (such as antacids or proton pump inhibitors like omeprazole or Nexium) may not get the full dose.
Calcium citrate does not need to be taken with food, does not require stomach acid to break down, and will be absorbed the same whether it is taken with food or without. Patients who have problems with intestinal absorption (for example, patients who have had gastric bypasses) will likely be better off with calcium citrate.
Another note on absorption: For those who have had a gastric bypass or have chronic diarrhea, a chewable or gummi form of calcium may be preferable to a hard pill. The chewable and gummi forms break down in your mouth rather than in the stomach and intestines, giving you gastrointestinal tract more time to absorb the calcium.
Some calcium carbonate supplements are much cheaper than other forms. Tums is commonly sold for the treatment of heartburn, but it consists of calcium carbonate and can be used as a cheap supplement. Other forms of calcium tend to be more expensive.
Elemental calcium refers to the amount of “pure” ionic calcium in the calcium compound, when you split the compound. Calcium carbonate contains a higher percentage of elemental calcium than any other compound: 40% of each pill is calcium. For calcium citrate, only 21% of the pill is calcium; the rest is citrate. The other forms have even lower percentages. Practically, if the percentage of calcium is lower, you need to take more pills (or larger pills) in order to get the same dose of elemental calcium. If your supplement contains calcium carbonate, the pill will be smaller (for the same dose) compared to calcium citrate.
Note: you shouldn’t need to use the above percentages to calculate the amount of calcium you are getting. The label will tell you the amount of elemental calcium, not the amount of the calcium compound. So if it says that each pill has 500 mg of calcium, it means elemental calcium. It may say “calcium (as calcium carbonate)” – that is telling you that they are giving you the elemental dose, but want you to know the compound providing it.
Calcium citrate is more readily absorbed in the intestines and has fewer side effects, which is why it is the form of calcium I recommend most often. For patients who have no difficulty with swallowing large pills, Citracal Maximum works well and is found in most pharmacies and supermarkets. For those who cannot tolerate large pills, or who have problems with absorption, I recommend a chewable calcium citrate such as BariMelts Calcium.
But some patients don’t tolerate Citracal, and some don’t like the way BariMelts tastes. That’s ok. Here is the thing: there is no single calcium that will work for everyone. The best calcium supplement is the one you will actually take every day.
If you want to take Tums, and your bowels are moving fine with it, then go ahead and take Tums. If you insist on getting chocolate-flavored supplements, go for it. If you just want to swallow one large pill rather than chew multiple gummis, that’s fine too. If you need to take calcium, then the one that you actually don’t mind taking every day is the right one for you. If you are disgusted by the supplement you are taking, or choke every time you see it, there is a pretty good chance you won’t keep taking it. You might have to experiment with a few different forms to see what you like best.
Check the serving size: One of the mistakes I see often is a miscalculation of how much calcium someone is getting. Here is how it usually happens: A patient will often look at the supplement bottle and see that a serving has 500 mg of calcium. I then tell her to take 1000 mg daily, or four pills. The patient, thinking that perhaps my math skills are a bit rusty, tells me that she will be getting 2000 units daily if she takes four pills. But my math was correct. The key is the serving size. In most calcium supplements, the “serving” consists of more than one pill. In Citracal and other calcium citrate supplements, the serving size is two pills. When the bottle advertises “500 mg per serving,” it means that there are 500 mg in TWO pills, or 250 mg in each pill. If you are not paying attention to the serving size, you may be getting a lot less calcium than you think.
Don’t take them all at once: Your intestines can only absorb so much calcium at a time. You will increase the amount of calcium you get if you spread out the doses throughout the day. Someone taking 2 pills in the morning, afternoon, and evening will absorb more calcium than someone taking 6 pills all at once, even though they are consuming the same dose.
Be aware of interactions with medications: Calcium interferes with the absorption of certain medications, including thyroid hormone (levothyroxine or Synthroid) and some antibiotics (tetracycline and fluoroquinolones like ciprofloxacin). If you are on levothyroxine, wait four hours between taking it and calcium, or the calcium could cause you to receive a much lower dose of thyroid hormone. If you are on a short course of tetracycline or ciprofloxacin, consider holding your calcium on the days when you are being treated with antibiotics.
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