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:
- The amount of calcium we absorb from food
- The amount of calcium we excrete through the kidneys
- 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?
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.
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.