Absorption: Get The Most Out of Your Calcium Supplement

Updated: February 2, 2024

Lara Pizzorno is the author of “Your Bones: How You Can Prevent Osteoporosis and Have Strong Bones for Life – Naturally” and a member of the American Medical Writers Association with 29 years of experience specializing in bone health.

Recently we asked Lara if she would help us provide a series of short, ongoing videos to help you (our customers and readers) stay up to date on the latest facts and science related to bone health.

In this latest video, Lara talks about how to get the most out of your calcium supplement. Watch the video below (or read the transcript provided) and let us know what you think in the comments. 🙂

Hello, I’m Lara Pizzorno the author of “Your Bones” and I’m here today to share information with you that I hope will help you to have healthier bones.

Today I’d like to talk with you about what you need to know to ensure that you get the best amount of calcium from your supplement. There are potential mitigating factors, these are vitamin D adequacy, calcium dosage.

But first let’s talk about vitamin D. It’s very important that you ensure that you are getting adequate vitamin D to meet your needs, not the needs of some mythical average person, but your needs. This is why, in addition to stomach acid your ability to absorb any form of calcium: calcium in the food that you eat or supplement, is greatly affected by your vitamin D status. We absorb calcium both actively and passively in the small intestines but that amount that we absorb passively is quite small. Active absorption are a primary means of absorbing calcium and active absorption requires vitamin D.

In individuals who are vitamin D deficient only 10-15% of the dietary or supplemental calcium they consume is absorbed.

And the better your vitamin D status, the better you will be able to absorb calcium. Remember that I wrote about this in “Your Bones” – optimal levels of vitamin D are 50-80 nanograms per mL. The way that this is checked is a simple blood draw test that measure the amount of 25OHD that circulates in your bloodstream. If you haven’t had this test run to determine what your vitamin D status is, please ask your doctor about having this done. Most insurances cover it and it’s not a very expensive test, it’s just a blood draw. Ideally you would also like to be tested in the winter months and the summer months because you may find that you need higher amounts of vitamin D supplementation in the winter when sun exposure is so much less.

So let’s talk about a couple of studies that show how important vitamin D status is for absorption. In one study they compared how much calcium absorption in individuals with different blood levels of vitamin D and they found that those whose blood level vitamin D were slightly higher, at least 34.5-36 ng/mL, which still isn’t’ very great but it’s better than quite frankly deficient, these individuals were able to absorb 65% more calcium than those whose blood levels of vitamin D averaged 20 ng/mL or lower.

In another study they looked at 23 vitamin D sufficient postmenopausal women and they compared their ability to absorb calcium from calcium carbonate or calcium citrate. So in other video clips I’ve talked about the myth that calcium citrate is somehow more bioavailable than other forms of calcium. In this study, the researchers found that being vitamin D sufficient was far more important than what form of calcium, whether it was calcium citrate or carbonate was ingested. The researchers measured the women’s levels of ionized serum calcium, total serum calcium, parathyroid hormone levels and how much calcium they excreted in their urine over a 24 hour period. And what they found was that the bioavailability of calcium from calcium citrate was no better than calcium carbonate in the women who were vitamin D sufficient.

So a very important point to make here is that bones are not just calcium they contain and they require many other minerals and vitamins besides vitamin D to maintain healthy bone density. And the very term bone mineral density makes this point, we don’t check for bone calcium density, we check for bone mineral density.

In future videos we’ll talk about the role that each of the many nutrients that our bones require plays, but we don’t have time now to discuss this in depth, that’ll be coming up. What I’d like to talk to you still in this video clip is how important it is to take your calcium supplement and consume calcium in smaller doses throughout the day rather than in one dose. Why is this important? Because absorption of calcium is greatest when the amount consumed at one time is lower and the need is higher. This was very dramatically shown in a study that compared the bioavailability absorption of different forms of calcium in 37 healthy men and women and what they found was that more calcium was absorbed when a lower dose was taken. 36% of the calcium was absorbed when a 300-350 mg dose was taken and only 28% of the calcium was absorbed when the subjects took 1000 mg all at once.

The researchers determined that for this reason, the maximum amount dose of elemental calcium that should be taken at one time is 500 mg and 350mg taken twice daily was likely to provide the best absorption of elemental calcium. You may be thinking that the best level of calcium absorption is just 36% of the elemental calcium that was consumed when a 350 mg dose was taken, but what about the rest of the calcium? 64% of the calcium that passes out of your body through the digestive tract – is this simply wasted or does it provide us with any benefit? It does provide us with some significant benefit and that will be the topic of our next video clip. Thanks for tuning in!


Heaney RP, Dowell MS, Hale CA, Bendich A. Calcium absorption varies within the reference range for serum 25-hydroxyvitamin D. J Am Coll Nutr. 2003;22:142–146. PMID: 12672710

Heaney RP, Dowell MS, Bierman J, Hale CA, Bendich A. Absorbability and cost effectiveness in calcium supplementation. J Am Coll Nutr. 2001;20:239–246. PMID: 11444420

Straub DA. Calcium supplementation in clinical practice: a review of forms, doses, and indications. Nutr Clin Pract. 2007 Jun;22(3):286-96. PMID: 17507729

Heaney RP, Dowell MS, Barger-Lux MJ. Absorption of calcium as the carbonate and citrate salts, with some observations on method. Osteoporos Int. 1999;9:19–23. PMID: 10367025

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  1. Stuart

    April 8, 2017 , 1:35 pm

    Hi Laura, I am confused about the amount of calcium needed from supplements and or food. If only a third of the calcium is absorbed would you not need ingest 3000 mg of calcium to absorb 1000mg elemental calcium or is the needed elemental calcium absorbed only 350mg? Thanks.

  2. Monica

    April 9, 2017 , 9:21 am

    Hi Stuart,
    No, you should not be taking 3000 mg of calcium per day. It is recommended for men 50 or better to be taking 1000 mg or 1200 mg if you are 71 or better (from all sources: both food and supplements) of calcium per day. The Standard American Diet typically provides around ~500 mg. So you would still need an extra 500 -700 mg through supplementation.

    As Lara has explained, taking it in doses of 500 mg or 350 mg at a time increases the absorption of elemental calcium up to 36%. While this means some passes out of your body – it is still extremely beneficial. You can see that video here: https://blog.algaecal.com/lara-pizzorno-the-benefits-of-unabsorbed-calcium-in-your-digestive-tract/

    AlgaeCal, for instance, shows the calcium it provides in elemental calcium.

    So in summary – depending on your age you should be taking anywhere from 1000 mg to 1200 mg per day of calcium, from all sources including food and supplements.

    – Monica

  3. Michelle Kaufman

    March 26, 2024 , 1:32 pm

    I’ve read that green tea helps add bone density, & then another article says it washes calcium out with your urine. Now I’m not sure if it’s beneficial or not.

  4. Manja AlgaeCal

    March 27, 2024 , 7:30 am

    Thank you for sharing your thoughts, Michelle! It’s understandable to feel uncertain when conflicting information arises about the effects of tea on bone health. While some studies suggest that green tea may promote bone density, others caution about potential calcium loss through urine.

    To provide more clarity on this topic, I recommend checking out our article “The Bone Health Benefits of Tea.” This article delves deeper into the relationship between tea consumption and bone health, highlighting the potential benefits of polyphenols found in tea. You’ll find that, overall, tea can be a valuable addition to an overall healthy diet, and our article can offer further insights into maximizing its benefits.

    Remember, moderation and balance are key in enjoying the health benefits of tea. If you have any further questions or need additional information, feel free to reach out!
    – Manja

This article features advice from our industry experts to give you the best possible info through cutting-edge research.

Lara Pizzorno
MDiv, MA, LMT - Best-selling author of Healthy Bones Healthy You! and Your Bones; Editor of Longevity Medicine Review, and Senior Medical Editor for Integrative Medicine Advisors.,
Dr. Liz Lipski
PhD, CNS, FACN, IFMP, BCHN, LDN - Professor and Director of Academic Development, Nutrition programs in Clinical Nutrition at Maryland University of Integrative Health.,
Dr. Loren Fishman
MD, B.Phil.,(oxon.) - Medical Director of Manhattan Physical Medicine & Rehabilitation and Founder of the Yoga Injury Prevention Website.,
Prof. Didier Hans
PHD, MBA - Head of Research & Development Center of Bone Diseases, Lausanne University Hospital CHUV, Switzerland,