6 Calcium Absorption Facts You NEED to Soak Up

Updated: March 27, 2023

Supplement capsule zoomed in

Picture a classroom full of students taking the same course.

Also, imagine if you can that they all have perfect attendance during the year. What is the chance that they will get the exact same score, come exam time? Very low, right? And that is in large part because their ability to absorb information is very different from each other.

You can make a similar comparison with calcium.

Statistics show we Westerners get the most calcium in the world, but still suffer from the highest rates of osteoporosis. Why? In part because of an inability to fully absorb it.

Dr. Elson Haas, writer of “Staying Healthy with Nutrition,” states that 30-80 % of dietary calcium is not absorbed by the body. Other study results found that pre- and menopausal women absorb anywhere from 17-58%.

Calcium supplement makers, knowing this is a hot topic, advertise that their product absorbs better than their competitors. This implies that absorption is simply settled by what calcium supplement you buy.

Seems believable – but only because they omit many other factors that affect absorption rates. They do because each of the ‘other factors’ are common to all products, and so that would water down the unique claim they make about their product’s absorption rates.

The truth is your ability to absorb matter depends on many factors. Added up they can determine whether you pass or fail a school test, AND whether you pass or fail a DEXA exam (the test that measures bone density).

Let’s look at what affects how much calcium you can absorb, and what you can do about it— your bones depend on it!

1. Stomach Acid – Known medically as hydrochloric acid (HCL), it is critical for good digestion and the absorption of nutrients. HCL is so concentrated that if you place a drop on a piece of wood, it will eat right through it.

But good news! Your stomach does not digest itself, thanks to a bicarbonate-rich solution that coats the mucosa (your stomach’s inner layer). Bicarbonate is alkaline, which neutralizes the acid, producing water in the process. But if your body overproduces acid, the bicarbonate solution is overwhelmed and it can lead to gastric ulcers.

The act of eating kickstarts the stomach to start secreting HCL. But it’s not HCL that breaks down your food or vitamins. Instead, the main role of HCL is to activate the main cells in the center of the stomach to start producing a protein-digesting enzyme called pepsinogen. Once activated it is called pepsin. After about 20-30 minutes when stomach acid and pepsin gets high enough they start to kill bacteria, viruses and parasites that accompany the food, as well as neutralize enzymes from the mouth. Then digestion begins.

2. Vitamin D – induces the synthesis of a carrier protein for calcium, called calbindin, in the intestinal epithelial cells. D works in the digestive tract to absorb calcium into the bloodstream from the first part of the small intestine. Called the duodenum, it’s where calcium is absorbed from food or supplements into your body through the intestinal wall- into your bloodstream.

Optimal vitamin D levels also help to maintain proper blood calcium level, which is essential to cardiac function. And taking calcium within 2 hours of receiving sunlight exposure allows vitamin D to increase calcium absorption.

3. Parathyroid hormone – Calcium across the membrane of intestinal cells is increased or decreased due to your level of parathyroid hormone (PTH).

Parathyroid hormone initiates this process, but indirectly, by stimulating production of the active form of vitamin D in the kidney.

4. Lactose – Calcium absorption in infants is increased with lactose. Intestinal microbial flora acts upon lactose which increases acid, making calcium more soluble.

5. Your Need for calcium – The amount you absorb calcium increases according to body demands. During pregnancy, lactation and adolescence for example, absorption efficiency increases by 50%.

6. Type of Calcium – Despite what various calcium products claim, all calcium types (be they from rock, shell, bone or plant) have similar absorption rates. All calcium salts absorb from 23 – 37% if taken with food. The extremes of 4% to 100% some advertise are marketing hype and simply not true.

calcium supplement algaecal

Image by HealthGauge on Flickr


Calcium absorption can vary greatly, not due to the supplement you choose, but the ‘other’ factors listed above. Supplement sellers claim superiority over competitors to get your sale, but the reality is they are mostly similar. There are no studies showing a correlation with fractures and absorption rates.

But your risk of breaking bones is proven to go down the more your bone density goes up. That is what the talking point should really be.

If you dig deep enough, you will find that the products that put absorption rates on a pedestal do so because their supplement cannot increase bone density. The research proves traditional calciums only slow down bone loss.

Don’t get sucked into the misleading marketing manipulation of absorption!

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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,