Calcium: What’s best for your bones and life?

You need calcium for life. Although 99 percent of the calcium in our bodies is stored in those strong bones and teeth, calcium is kept within a very tight concentration in your blood to support nearly every process in our bodies. Calcium helps our blood cells form, is required for clotting, is used by all of our electrical cells (nerves to send messages and muscle to contract), calcium keeps the acidity of your blood stable, and is used in the process of making just about every hormone including vital reproductive functions.

If you don’t get enough calcium for your body’s needs, especially growing bones, healing from injuries, and lactating new moms, your body grabs calcium first from your muscles (which you feel as cramping and pain) and then from your bones (demineralization and osteoporosis).

Gosh there sure are a lot of calcium supplements; how to choose?

Carefully! It that depends a whole lot on some other things…

1.    understanding the different forms of calcium and how much you are actually getting:

Some of the most common forms of calcium supplements that are available include: calcium carbonate, oyster shell calcium, calcium gluconate, calcium citrate, calcium citrate-malate, calcium hydroxyapatite, calcium lactate, calcium lactobionate…

The label of high quality products will tell you the amount of elemental calcium in the supplement; and then tell you which form: which salt or chelate carrier compound the calcium is attached to, e.g. “calcium carbonate.” But cheaper brands don’t break this out—in fact, make that your first clue.

understand calcium bioavailability from calcium supplement label

For example, this label says it gives 1000 mg of calcium carbonate. That’s a bit deceiving. Calcium carbonate is 40 percent elemental calcium, so 1000 mg of calcium carbonate contains 400 mg of elemental calcium. Calcium carbonate is one of the most widely used in supplements; it is inexpensive and has a higher portion of elemental calcium. Is it absorbed? Not so well for reasons we’ll discuss.

2.    Understanding how much you can absorb: Bioavailability

Most Americans are well below the Recommended Daily Allowance of 1,000-1,200 mg/day for calcium.

You might think that when you eat food, every vitamin, every mineral, every anti-oxidant, every protein… it contains is used by your body with total efficiency, but that’s not exactly the case.

It gets tricky: At one time it was believed that the better a substance dissolved in water, the more it was absorbed by the body, and therefore more bioavailable. While many studies made this assumption, water solubility doesn’t translate into absorption in the body.

Bioavailability” refers to the amount of an ingested nutrient that will be absorbed and used in bodily processes.

Not all of the nutrients in our food (or supplements) are absorbed; not all of what is absorbed is used in the body.

Here’s the calcium sequence:

In the stomach, minerals are released from foods thanks to the stomach’s acid (low pH of 1.8-3.0) environment. When we take an antacid or acid-suppressing drug, we do not release minerals, they remain bound to their food (or their “chelate”, when talking about supplements). Minerals bound to food or chelate cannot be absorbed. Why do they stay unavailably bound? Antacids increase the pH of stomach. This post explains how low stomach acid causes indigestion.

The vast bulk of mineral absorption occurs in the small intestine. Cells lining the small intestine actively absorb calcium, transport calcium across the cell into blood and lymph capillaries on the other side. This process is entirely dependent on adequate vitamin D levels in order to make enough of the calcium carrier protein, calbindin.

If you flood your stomach, and then your intestine with lots of calcium, it will be absorbed into your blood. This doesn’t occur using the normal, highly regulated, small intestine mechanisms, but rather by dissolving through the barrier junctions between intestinal cells.

Your heart pumps blood, calcium is delivered: or is it? Herein lies the problem of taking the wrong supplements.

Flooding your stomach, and then your intestine with lots of calcium, spikes blood calcium levels. Three hormones keep blood calcium levels constant:

  • parathyroid hormone (PTH – produced by parathyroid gland) causes the kidneys to conserve calcium so it is not eliminated in urine. PTH also demineralizes your bone by telling specialized bone cells to pull calcium out for use elsewhere.
  • calcitriol (active vitamin D – made from cholecalciferol obtained either from sun exposure, food or from synthetic vitamin D3 supplements) tells cells in your small intestine to absorb more calcium and mobilizes calcium out of bone stores. Responding to the high blood calcium from some supplements, the parathyroid stops making PTH, your kidneys stop activating vitamin D, and less calcium is absorbed or removed from bone. BUT active D is used in many systems including immune function. It is needed by the body.

Over-worked or failed kidneys cannot activate vitamin D3 to calcitriol.

  • calcitonin (mostly made by your thyroid, but also lung and intestines) tells the body to move high blood calcium into bone and tells the kidneys not to rebsorb calcium (as well as other electrolytes) but to eliminate them in urine.

Flooding the blood with too much calcium shuts down making PTH and activating D3. But the high blood levels can combine with phosphate ions, forming deposits of calcium phosphate (stones) in blood vessels and in the kidneys. More on this below…

Important: Other factors affecting calcium absorption and use

Even if you’re getting the right type and amount of calcium, there are other factors that may be working against you:

  • Vitamin D deficiency reduces calcium absorption
  • Oxalates (think spinach) and phytates (think grains and beans) reduce calcium absorption. These compounds bind calcium and prevent intestinal absorption.
  • Deficiencies in other vitamins, minerals and trace minerals like vitamin K, magnesium, zinc, copper, manganese, strontium and boron among others can contribute to poor bone health. Sometimes calcium is not absorbed because your body needs other trace minerals.
  • Getting regular weight-bearing exercise? Helps your body to better use the minerals and the calcium that you consume to stimulate bone growth.
  • Taking calcium supplements? Too much will cause you to absorb less. It’s the body’s natural way of protecting itself. Best not to guess at this. Get checked. We use Nutrition Response Testing® to see which form of calcium is right for you, with which synergistic other nutrients, and in what amounts. If high calcium is needed, we split your dose throughout the day.
  • Excessive sodium, caffeine and alcohol intake can stimulate the kidneys to dump calcium.

Here is how calcium gets a bad wrap

Kidney stones?

Magnesium prevents formation of calcium oxalate stones. It is important to balance any calcium source with magnesium. Most whole foods that are high in calcium are also high in magnesium. Why? In plant sources magnesium is the central mineral to chlorophyll. All plants have magnesium and you will get plenty if your stomach acid is sufficient to release the magnesium (and calcium). Animal products (cold water fish and pastured animals) are also high in magnesium due to the complex regulation of calcium, magnesium, and other minerals by their bodies. Generally speaking, most people need twice the magnesium as calcium.

But when we take a lot of calcium in supplement form, special calcium receptors in the kidneys cause the nephrons to filter out not just calcium; the kidneys will also waste potassium, sodium, magnesium, chloride, and water. In the kidney nephrons, excessive calcium can combine with phosphorous and form stones.

Urinary tract infections?

If you supplement the wrong calcium form or type, your kidneys will remove calcium from your blood. Abnormally high urinary calcium increases the risk of developing UTIs.

Blood clotting?

Recent research suggests heart risk is 30 percent higher in people who use commercial calcium supplements. In contrast, calcium in food and balanced whole food sources that include sufficient D and magnesium have not been linked to heart problems.

Why? The answer is unclear, but likely due megadoses in pill form that cause a sharp rise in blood calcium levels in contrast to whole food sources that provide balanced minerals and other nutrients. High dose, synthetic calcium supplements cause problems by:

  • by decreasing magnesium absorption
  • by promoting arterial calcification, leading to increased blood pressure. Here’s how this works:

It is most likely that calcium (just like cholesterol) is the initial response to damage from other causes of inflammation. Nutrient deficiencies in other minerals, vitamins, and/or presence of inflammatory risk factors are more directly involved in cardiovascular problems.

However, when intestinal calcium absorption floods the blood with high elemental calcium, in the alkaline blood calcium binds to phosphorous and precipitates out binding to blood vessel walls.

It’s best to get your calcium from whole foods and use Nutrition Response Testing to evaluate which supplements to take and at what doses:

Your best sources of absorbable calcium are these whole foods:

Sardines (3 oz) 371 mg
Sesame seeds (1 ounce) 280
Tofu – organic, fermented (3 oz) 190
Salmon (3 oz, canned) 180
Collards (1/2 cup, chopped) 180
Rhubarb (1/2 cup) 174
Amaranth flour (1/2 cup) 150
Spinach (1/2 cup, canned) 136
Figs (5) 135
Artichoke (1 med.) 135
Soybean nuts – organic (1/4 cup) 116
Turnip greens (1/2 cup, chopped) 100
Kale (1/2 cup, chopped) 90
Almond butter (2 tbsp.) 86
Beet greens (1/2 cup) 82
Almonds (1 ounce) 80
Bok Choy (Chinese cabbage) (1/2 cup) 79
Okra (1/2 cup) 77
Tempeh – organic, fermented (1/2 cup) 77
Beans (1/2 cup, baked) 75
Papaya (1 medium) 73
Broccoli (1/2 cup, chopped) 47


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Ellinger I. The Calcium-Sensing Receptor and the Reproductive System. Frontiers in Physiology. 2016;7:371. doi:10.3389/fphys.2016.00371.

Gaby A. 2011. Nutritional Medicine. Fritz Perlberg Publishing: Concord, NH.

Riccardi D, Kemp P. The calcium-sensing receptor beyond extracellular calcium homeostasis: conception, development, adult physiology, and disease. J.Annu Rev Physiol. 2012; 74:271-97. Epub 2011 Oct 17.

Marie Sternquist

Marie Sternquist, MS CHHC is a graduate of the University of Colorado, with 30 years of health-related clinical research published peer-reviewed medical journals, Marie's interests lie in how chemical and metal toxicities affect our health, hormones and immune function—and how to heal these problems with whole foods. In 2014, Marie completed the Health Coach program at the Institute for Integrative Nutrition where she studied 100’s of dietary theories with an emphasis on developing step-by-step nutritional programs and is currently working on her Nutritionist certification through the Masters in Functional Nutrition program and the University of Western States. Marie’s signature nutrition programs have helped thousands of people just like you regain health and quality of life. In 2016, Marie Sternquist completed her Advanced Level in Nutrition Response Testing®, joining her husband Dr. Greg Sternquist as an advanced clinician. Marie is also a wilderness explorer, skier, photographer and mom. Visit her at and

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