Calcium: What you need to know

Calcium structures the human skeleton. Most people are aware of that. Because of this, people often supplement calcium for bone health. For the typical person, however, I’m not a big fan of this practice.

Why? Because considerable data link supplemental calcium to increased risk of cardiovascular disease. Even in patients without kidney problems, supplemental calcium could be risky—there are loose correlations linking calcium supplementation to the later development of certain breast cancers, for example.

I’m not saying that calcium is bad for you. It’s an essential mineral for building bone and running your nervous system. What I’m saying is that supplemental calcium is questionable.

Most of your calcium should come through diet because (in reasonable amounts) dietary calcium doesn’t seem to carry the same risks as supplemental calcium.

It’s hard to overdo any single nutrient in food form. When you consume calcium in kale or sardines, it doesn’t spike blood levels like a supplement does. Rather, it trickles into your bloodstream through the process of food digestion. That’s how nature intended it.

At the end of the article, I’ll talk more about how to get enough calcium through diet. It’s not too complicated, but it may require a bit of planning. Right now, though, let’s cover why calcium is important.

What Calcium Does For You

About 98% of bodily calcium is found in bone. That’s because the primary role of calcium is to structure bones, teeth, and other components of the human skeleton.

The formation and deformation of bone is a lifelong process. Through puberty, calcium needs go up to support rapid bone formation, eventually stabilizing in young adulthood. But as we continue to age, bone density begins to decline. Should we consume more calcium to mitigate this decay?

Unfortunately, it’s more complicated than that. If you remember one thing from this article, remember this: bone health isn’t merely a matter of calcium status.

Yes, you need calcium to build bone, but you need nutrients like vitamin D, vitamin K2, and phosphorus too. I’ll describe this system more thoroughly in the next section.

Let’s move on from bone health though, because calcium is also an electrolyte.

An electrolyte? Yes, a mineral that carries an electrical charge in a solvent. (Water is the universal solvent.) Specifically, electrolytes regulate the membrane potential of your cells, allowing nerve impulses to fire.

In other words, electrolytes like sodium, potassium, and calcium facilitate the proper functioning of your nervous system. They keep your mind humming, your muscles contracting, and your heart beating.

The concentration of calcium in extracellular fluid directly impacts these functions. It’s why low levels of calcium (hypocalcemia) can cause muscle cramps or muscle weakness, and high levels of calcium (hypercalcemia) can cause irregular heartbeat.

Calcium, Vitamin D, and Phosphorous

Calcium status is closely linked to vitamin D and phosphorus status—and both a vitamin D deficiency and a phosphorus overload can impair calcium uptake into bone. Some combination of these factors generally explains the development of bone density issues like osteopenia and its more serious cousin, osteoporosis.

About 41.6% of US adults are deficient in vitamin D, a nutrient synthesized when sunlight hits the skin. Poor vitamin D status, poor bone health. Should we be surprised that brittle bones are so common? (Note: vitamin D supplements are super helpful for folks who tend to get little sun exposure.)

Phosphorus overload is yet another consequence of modern living. Grains, dairy, and processed foods—all high in the modern diet—are also high in phosphorus. This is bad news for our collective bone health.

More rarely, you see an excess of vitamin D—and this causes a different problem: excess calcification of soft tissues. This problem can impact the heart, breasts, kidneys (as kidney stones), blood vessels, and elsewhere.

Hard tissue calcification is generally desirable. Soft tissue calcification is definitely not.

I’ll briefly mention two hormones that regulate blood calcium levels: calcitonin and parathyroid hormone (PTH).

When calcium levels get too high, calcitonin is released to stop calcium loss from bone. And when calcium or vitamin D gets too low—or phosphorus gets too high—PTH kicks in and tells your bones to release calcium. Then serum calcium normalizes at the expense of bone density.

Calcium Deficiency Causes and Symptoms

The main cause of calcium deficiency is inadequate intake of dairy, edible bones, cruciferous vegetables, and other calcium-rich foods. As you might imagine, calcium deficiency is common in dairy-intolerant folks.

Excess phosphorus can also impair calcium absorption and exacerbate calcium deficiency. Almost nobody eating sufficient calories requires more phosphate.

The symptoms of calcium deficiency aren’t usually noticeable. True symptoms occur with hypocalcemia, but that level of electrolyte disturbance isn’t typically caused by a nutritional imbalance alone.

Because your body pulls calcium from hard tissue to maintain blood levels, the signs of calcium deficiency mostly relate to bone health. These include:

  • Osteoporosis: A condition of impaired bone density and higher fracture risk.
  • Osteopenia: A less serious precursor to osteoporosis.
  • Rickets: A disorder of skeletal deformities, brittle bones, and weakness that primarily affects children.

A severe calcium deficiency can also provoke a constellation of spasms, muscle weakness, and tremors called tetany.

Calcium Excess Causes and Symptoms

Consuming too much calcium can provoke a temporary state of hypercalcemia. Eventually the excess calcium is shed via urine, but not before some of it sticks in soft tissue.

Soft tissue calcification is especially problematic in the circulatory and renal systems. For example, higher levels of coronary artery calcium (CAC) are correlated with an increased risk of heart attack, stroke, and cardiac death. The CAC score isn’t a perfect predictor of risk, but it’s still a useful biomarker.

High urinary calcium excretion (a sign of calcium overload) also drives the formation of kidney stones. These stones are made of calcium oxalate and can be excruciatingly painful to pass.

Beyond excess calcium intake from supplements or (more rarely) food, other causes of hypercalcemia include:

  • Impaired kidney function or kidney disease
  • Vitamin D toxicity
  • Being at risk for the calcium-alkali syndrome (pregnant women, bulimics, and elderly women, primarily)

Let’s talk about dietary calcium now.

Best Dietary Sources of Calcium

I recommend getting your daily calcium through diet whenever possible. Unlike excess supplemental calcium, adequate dietary calcium isn’t linked to higher heart disease risk.

Here’s a partial list of calcium-rich foods:

  • Yogurt (296 mg per cup)
  • Kale (94 mg per cup)
  • Sardines with bones (347 mg per 3.2 ounces)
  • Salmon with bones (181 mg per 3 ounces)
  • Spinach (246 mg per cup)
  • Turnip greens (198 mg per cup)
  • Sesame seeds (351 mg per ¼ cup)
  • Broccoli (62 mg per cup)
  • Cheese (204 mg per 1 ounce)
  • Cow’s milk (138 mg per 4 ounces)
  • Tofu (775 mg per 4 ounces)

As you can see, you don’t need to consume milk products to stay calcium sufficient. But if you are sensitive to lactose, casein, or other milk components, you’ll have to work harder. Just prioritize cruciferous vegetables and eat canned fish (with bones) and you’ll get there.

One last point is that you don’t absorb calcium equally from all foods. People generally absorb 20-40% of milk calcium, and an even higher percentage from soft bones and cruciferous vegetables.  Spinach calcium, however, is only about 5% bioavailable. That’s because spinach is high in oxalates that bind to calcium and inhibit its absorption.

Testing Calcium Status

Most people think a normal serum calcium result rubber stamps their calcium status. But that’s a common fallacy. Normal serum calcium just means your homeostatic mechanisms—PTH, calcitonin, kidney function, etc.—are keeping blood calcium levels within a normal range. It doesn’t mean you’re consuming optimal calcium for skeletal health.

Assessing calcium status for bone health is a capacious topic, and I won’t be able to do it justice here. But I will mention a few relevant tests.

  • PTH: If PTH is elevated, it may indicate calcium deficiency, vitamin D deficiency, or phosphorus overload.
  • 25(OH)D: This is the standard vitamin D test. Lower levels (below 30 ng/mL) can impair bone absorption of calcium.
  • Calcitonin: High calcitonin level suggests excess calcium intake.
  • Osteocalcin: Low levels of this bone formation marker are linked to osteoporosis in women.
  • Urinary calcium excretion. Higher levels may indicate accelerated bone loss.

I wish serum calcium could biomark calcium deficiency, but I also wish I could teleport myself to Aruba and back. Neither are possible.

How To Get Enough Calcium

How much calcium do you need? The short answer is about a gram per day.

To expand on this, the recommended dietary allowance (RDA) for calcium is 1 gram for men and women ages 19-50, 1 gram for men between 51 and 70, 1.2 grams for women between 51 and 70, and 1.2 grams for men and women over 70. Check out this chart if you want the RDAs for infants and children of various ages.

To dial in your calcium, log your meals in an app like Cronometer for 1-3 days. Doing this dietary assessment will tell you where you stand on calcium, along with your other macros and micros.

If you’re short on calcium, bump it up with dairy, edible bones, and green vegetables. Try to skip calcium supplements to avoid the risk of soft tissue calcification.

This concern influenced our decision to leave calcium out of LMNT. Plus, our direct review of our Ketogains clients showed us that nearly all of them were already getting enough calcium.

This doesn’t mean that their bone health was perfect. Bone health depends on exercise habits, vitamin D status, kidney health, phosphorus intake, genetics, and many other factors.

Calcium is necessary but not sufficient for building and maintaining bone. It’s just one piece of the puzzle that you need to get handled.