The Many Roles of Calcium

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By Roberta H. Anding, MS, Baylor College of Medicine and Texas Children’s Hospital
Edited by Kate Findley and proofread by Angela Shoemaker, The Great Courses Daily

You probably know about calcium’s role in building bone, but did you know it also plays a vital role in our nervous system? Professor Anding dives into calcium and the dangers of deficiency.

Calcium rich foods
Besides strengthening bones, calcium is essential for secreting and regulating hormones and enzymes and sending messages throughout the nervous system. Photo By Tatjana Baibakova / Shutterstock

Calcium’s Roles

Calcium is the most plentiful mineral in the human body, and it plays several significant roles. As one of the skeleton’s primary building blocks, we find more than 99% of the body’s total calcium in our bones and teeth, where it provides structural support. 

The rest—less than 1% of calcium—is found throughout the body. It is located in the fluid between cells, in the blood, and in the muscles. 

Outside of the function of calcium in bone, calcium plays many roles in secreting hormones and enzymes and regulating their activity. It sends messages throughout the nervous system, is involved in blood clotting, and aids in blood vessels and muscle contraction and expansion. 

Additionally, calcium contributes to normal heart rhythm. Thus, beyond bone, calcium plays vital roles in human nutrition.

So these important processes can take place efficiently, body fluids and tissues must maintain a constant level of calcium. The skeleton stores calcium and other minerals.

If the blood calcium is too low—it has to be within a normal range—the body replenishes it with calcium that was stored in the bones. The bones become a reservoir for extra calcium. 

Sources of Calcium

A cup of skimmed milk has about 300 milligrams (mg) of calcium. 3.5 ounces (oz) of salmon canned with the bones has 380 mg. Thus, if you’re making salmon patties or croquettes, you’ve got to mash the bones; don’t discard them. A half a cup of tofu has 130 mg of calcium.

How much calcium do you need? The daily reference intake (DRI) for males and females in the age category of 19 to 50 is 1,000 mg per day.

If you’re getting calcium predominantly from milk, that’s over three glasses of milk per day. For males and females between the ages of 51 and 70, the DRI is 1,200 mg per day. 

Now, there is an upper limit. The maximum amount of calcium you should consume per day is 2,500 milligrams. 

As with most nutrients, this is an example where more does not equal better. The amount of calcium absorbed at one time is about 500 mg, and if it’s taken with other competing minerals, the absorption will be less than this. 

If you’re taking calcium as a supplement, and you need to take more than this, divide the dose. In general, the doses should be between four and five hours apart, but again, this can be influenced by the meal composition and your own individual state of health.

Deficiencies and Excess

Calcium deficiency per se is not often detected because there’s a lack of symptoms until an extensive amount of bone mass has been lost. Diets high in protein and sodium can limit the bioavailability of calcium. So, as Americans consume more and more protein in their diet, there may be a negative impact on calcium status. 

When the reservoir of calcium in your bones is depleted, bone fractures can occur under very minimal stress. Low calcium intake can lead to osteoporosis, a disorder characterized by weak and porous bones and a bone mineral density score of greater than -2.5. In those diagnosed with osteopenia, bone mineral density is lower than optimal, but not enough to be diagnosed with osteoporosis.

Bones are a dynamic tissue and are constantly going through resorption, which is bone breakdown, and deposition, or bone formation. As people grow older, the amount of resorption and deposition are altered. 

More formation and less breakdown occurs during childhood. Older individuals have the reverse.

“I oftentimes say that you get one shot to build a skeleton, and that is during the period of rapid bone formation, ages 11 to 24, so if you miss this very rapid bone formation time, you don’t get a do-over later in life,” Professor Anding said.

In early middle-adulthood, resorption and deposition are nearly the same. In aging adults, and particularly in post-menopausal women, resorption surpasses deposition, and the result is bone loss. 

This bone loss increases the risk for osteoporosis. Some studies suggest within the first year after menopause, where most bone loss occurs, up to 7% of bone could be lost. 

Calcium alone doesn’t improve bone mass. Weight-bearing exercise, in addition to diet, can help to reduce the loss. Make sure to include strength training, both lower and upper body, to maximize that.

Conditions such as anorexia nervosa, a lack of adequate intake of calories and vitamin D, and a lack of weight-bearing exercise will contribute to bone loss in young women. Rickets can occur when vitamin D intake is inadequate, and that limits the amount of calcium that’s being absorbed. 

Outside of bone, the risk of inadequate calcium intake can lead to increased risk of high blood pressure. Some studies also suggest an increased risk of colon cancer linked with poor calcium intake, but the results are conflicting.

On the other hand, excess intake can lead to a condition called “hypercalcemia,” which means elevated blood calcium. However, this is often due to excessive vitamin D intake and rarely from diet alone. 

In individuals suffering from cancer, hypercalcemia may be present due to the effect of cancer on the bone. Essentially, cancer that has metastasized to bone can chew up the bone and release the calcium. As a diagnosis, hypercalcemia itself can result in fatigue, depression, confusion, loss of appetite, nausea, vomiting, constipation, pancreatitis, increased urination, and a decreased mineral absorption.

This article was edited by Kate Findley, Writer for The Great Courses Daily, and proofread by Angela Shoemaker, Proofreader and Copy Editor for The Great Courses Daily.

Professor Roberta H. Anding is a registered dietitian and Director of Sports Nutrition and a clinical dietitian at Baylor College of Medicine and Texas Children’s Hospital. She also teaches and lectures in the Baylor College of Medicine’s Department of Pediatrics, Section of Adolescent Medicine and Sports Medicine, and in the Department of Kinesiology at Rice University.

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