Calcium: The Real Story

One of the best kept secrets of nutrition is that nearly all body systems need nearly all nutrients. When we don’t get enough calcium, for example, it’s not just our bones that suffer, but the rest of our body as well.

The connection between calcium and bone health seems obvious, as calcium is what gives bone much of its strength. The amount of bone we have, particularly as we are growing, depends substantially on how much calcium we consume. But once we have amassed an adult skeleton, calcium still works to make bones strong, though in a surprising way. The body maintains blood calcium levels very tightly by making three adjustments, as needed:

  1. The amount of calcium we absorb from food
  2. The amount of calcium we excrete through the kidneys
  3. The amount of calcium we draw out of our bone reserves.

The third adjustment, the withdrawal of calcium from bone, is accomplished not by leaching calcium out, but by tearing down small volumes of bone and scavenging their calcium. This activity, known as bone remodeling, is just like the remodeling of a building, i.e., we tear out old structures and replace them with new. When calcium intake isn’t sufficient to meet the body’s needs, the rate of remodeling speeds up, so as to release more of the bone’s calcium. With bone, just as with our buildings, a structure being remodeled is fragile until the repair has been completed. Not surprisingly, therefore, a skeleton undergoing a lot of remodeling is much more fragile than a skeleton with less.

Calcium affects the rate of bone remodeling directly and immediately. If my intake of calcium is low today, the body doesn’t wait until tomorrow or next week to do something about it. It increases bone remodeling today, so as to access the calcium it needs today. And similarly, if I have been remodeling a lot of bone every day because my calcium intake is low, then today, when I get calcium intake back up to where it ought to be, remodeling immediately slows down. That’s the reason why, in so many of the studies showing an anti-fracture benefit of calcium, the effect begins immediately. One doesn’t have to wait to build up the skeletal mass (which changes at a rate of only a few percent per year).

What about other body systems?

Kidney Stones
One example may seem surprising. A high calcium intake lowers the risk of kidney stones. It might be natural to think: “Well, since I have had a kidney stone, I should reduce my calcium intake.” Actually, that’s the exact opposite of what you should do. Lowering calcium intake increases your risk of stones. The reason is that the commonest form of kidney stones consists not only of calcium, but of a substance called oxalate. Oxalate is a much more potent risk factor for stones than is calcium itself (even though calcium is a component of the stone). The oxalate in our urine comes both from internal metabolism and from our diet. When calcium combines with oxalate it becomes insoluble, and precipitates out of solution. If that occurs in the kidney, it can lead to stone formation, but if that complex occurs in the gut itself, where ingested yet unabsorbed calcium interacts with food oxalate, then that oxalate never gets into the body at all. So by increasing calcium intake, the oxalate doesn’t have to be excreted through the kidneys, and doesn’t contribute to stone risk.

Colon Cancer
There is yet another beneficial action of calcium within the intestinal cavity. Unabsorbed dietary calcium binds not only with oxalate, but with unabsorbed fat and bile acids as well. Both are irritants and tend to promote colon cancer. But, by binding them, calcium neutralizes these irritants and thus lowers the risk of adenoma recurrence or cancer development.

Hypertension and Weight Loss
And it doesn’t stop there. Calcium also helps in control of blood pressure, maintenance of body composition, and numerous other activities that sustain optimal health. For that reason, a high calcium intake should be part of the treatment regimen for patients with hypertension. It won’t always restore normal blood pressure by itself, but it definitely enhances the effect of blood pressure medications. So, too, if you’re on a weight loss diet, a high calcium intake helps – both to take pounds off and to keep them off.

There’s even more, but that’s another story.

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3 Responses to Calcium: The Real Story

  1. Nick Halpin - London UK says:

    Hi Professor Heaney

    Greetings from London. May I compliment you on a Fantastic blog /website. I will go through it with a fine tooth comb, but in the meantime can you please advise me on one important nutritional issue that confuses so many of us?

    There is a recent trend to say that cows’ milk isn’t a good (bio-available) source of calcium and not to drink it. Can you please advise on the bio-availablity of cows’ / goats’ milk to humans from your experience ? Many thanks, Nick

    • Robert P. Heaney says:

      Dairy products, and milk particularly, exhibit very good bioavailability of their Ca. I’ve measured that bioavailability in my lab hundreds of times and often use milk as the standard against which other Ca sources are measured. Dairy has the additional advantage of being an excellent source of high quality protein – in fact close to the best, if not the actual best – source of branched chain amino acids in our diets. Protein is necessary if Ca is to help us build or rebuild bone. Recall that bone is about 20% Ca by weight but 50% protein by volume. Protein released during bone remodeling can’t be re-used because many of its amino acids have been modified after incorporation into the collagen molecule, and are not able to bind to transfer RNA at the protein synthesis sites in the cell. Thus a supply of fresh dietary protein is essential if we are to get full benefit from our Ca intakes.

      The story about milk being a bad source is a flat-out lie, usually perpetrated by militant vegans who, unable to convince the majority of the public about the superiority of their life style, have resorted to scaring the public about the dangers of meat and dairy, or at least spreading lies about their efficacy.

      • Richard Kurylski says:

        Dear Prof. Heaney,
        I am sorry to say but your reply concerning “militant vegans” spreading lies about milk is highly exaggerated. There are doctors and scholars who are not vegans, not even vegetarians and who see danger in consuming milk. A modest example is Dr Lair Ribeiro, a Brazilian cardiologist and nutriologist who studied and worked in the States for 15 years. He says that according to the statistics, the Finns and the Swedes who consume the highest amount of milk per capita have a very high incidence of suffering from osteoporosis. On the other hand, in China and Vietnam, where milk is not consumed – osteoporosis is not a well-known disease. Besides he warns especially post-menopause women against taking calcium supplements, because they do not go to the bones but to the arteries helping cause atherosclerosis. He advocates taking vitamin D3 and magnesium and especially vitamin K2 that takes calcium from arteries to the bones. Some other doctors in America advise to take strontium and other minerals as well. The myth of calcium I suppose has been defeated.

        Apart from that, milk pasteurization also kills good bacteria and an absolute disaster is the so-called long life milk, in which proteins are completely disintegrated. Last but not least, hormones are widely used so that cows can increase production of milk and meat. And therefore the quality of milk in general is not recomendable

        What puzzles me is the fact that something is really going wrong with the Medicine nowadays. It is obvious that differences among scholars are healthy but not to the point where black is white for some and vice-versa for others. Other sticking points are cholesterol, soy, causes of hypertension just to name only a few. All that discredits modern medicine and no wonder that people start to turn their backs on traditional doctors who really stopped dealing with patients because they deal only with numbers – results of their respective analyses and the results of tests. The height of the heights is cancer. The reasons are well-known…

        We need more doctors like Dr Mark Hyman, because traditional medicine is digging its own grave. Perhaps we should not worry about that. The sooner, the better.
        Richard Kurylski, PhD

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