All About Calcium: How to Get Your Daily Recommended Intake

Calcium is responsible for important functions in the body like bone, brain, and heart health. You can reach your daily targets of calcium by consuming foods and supplements containing calcium — and not just dairy, as many may think. Keep reading to learn more about calcium and how you can make sure you’re getting your daily needs met.

What is the role of calcium?

Calcium is a mineral that is most frequently linked to strong bones and teeth, but it also plays a critical role in blood clotting, muscle contraction, regulating heartbeats, and nerve activity. Calcium also plays a pivotal role in other nutrients like Vitamin D absorption and magnesium balance. The body stores about 99% of its calcium in the bones, with the remaining 1% in blood, muscle, and other tissues.

How to get calcium naturally

There are two ways the body can get calcium. One way is through consuming calcium from foods or supplements, and the other way is by using calcium that already exists in the body by taking it from bones. The calcium that is "borrowed" from the bones should ideally be replaced by eating high-calcium foods.

A common misconception is that dairy is the main food sources of calcium, however calcium is widely available in many foods. Here is a list of some high-calcium foods:

• Dark green leafy vegetables. Broccoli, kale, collard greens, bok choy.
• Edible lean fish. Sardines and canned salmon.
• Dried fruits. Especially figs.
• Fortified foods. Cereals and fruit juices, and milk substitutes.
• Soy. Tofu and other soy products.
• Certain seeds. Sesame seeds and tahini.
• Dairy. Cheese, milk, and yogurt.

How much calcium do we need?

Here are the Recommended Dietary Allowances (RDA) for calcium per day:

*For pregnant and lactating women, the daily recommended dose of calcium is 1,000 mg.

Excess calcium consumption

When there is too much calcium in the blood, it is called hypercalcemia. The Upper Limit (UL) for calcium is 2,500 mg per day from food and supplements. Taking too much calcium can increase the risk of conditions like prostate cancer, kidney stones, constipation, and heart problems. Too much calcium can also interfere with iron and zinc absorption.

Hypercalcemia symptoms include:

• Nausea and/or vomiting.
• Shortness of breath.
• Chest pain.
• Heart palpitations and/or irregular heart rate.
• Weakness and fatigue.

Calcium bioavailability

Calcium is a large mineral and is not easily absorbed in the gut. The amount of calcium listed on the label of food is a measure of the calcium in the food, but not necessarily the amount absorbed by the body. The amount absorbed and used by the body is called 'bioavailability'. Some foods have higher calcium bioavailability than others.

Dairy products. Calcium bioavailability is about 30%, so if the milk label says 300 mg of calcium per cup, only about 100 mg will be absorbed and used by the body.

Plant foods. They contain less calcium, but their bioavailability is higher than dairy products. Bok choy contains about 160 mg of calcium in 1 cup (cooked), but because its bioavailability is higher, around 50%, that means 80 mg of calcium is absorbed. You can see that 1 cup of cooked bok choy and 1 cup of milk have comparable calcium content.

There is a downside to some plant foods and calcium, however. Some plant foods can contain naturally occurring substances called anti-nutrients. Examples of anti-nutrients are lectins, oxalates, and phytates. These can bind to calcium and reduce its bioavailability. Spinach contains the most calcium of all leafy greens, having 260 mg of calcium in 1 cup of cooked spinach. But it also contains a lot of oxalates, which lowers calcium bioavailability to only 5% (or 13 mg per cup cooked).

This isn’t a sign to stop eating spinach. It has a lot of other important micronutrients and health benefits. What it does mean is not to rely solely on spinach to reach your calcium targets.

Calcium deficiency

Severe calcium deficiency is called hypocalcemia and is caused by diseases such as kidney failure, gastrointestinal surgery, such as gastric bypass, or medications such as diuretics that prevent absorption.

Hypocalcemia symptoms:

• Abnormal heart rate.
• Muscle weakness and/or cramps.
• Poor or low appetite.
• Numbness or tingling in fingers or toes.

Progressive calcium deficiency can occur in people who do not get enough calcium from food for a long time, or who lose the ability to absorb calcium. This can lead to thinning of the bones over time as the body uses calcium from the bones to keep the rest of the body functioning.

The early stage of bone loss is called osteopenia, and if left untreated, it develops into osteoporosis. There are specific groups at risk for these conditions:

• Postmenopausal women.
• Women with amenorrhea.
• Those with milk allergy or lactose intolerance that do not consume enough calcium from other sources.

Beware that certain foods and medications can increase your calcium needs because they either decrease calcium absorption in the gut or increase calcium excretion in the urine. These include things like corticosteroids (like prednisone), excess sodium in the diet, phosphoric acid found in sodas, excess alcohol, and oxalates.

Calcium supplements

It may be difficult to get enough calcium, even with a healthy, balanced, diet. You may find reaching calcium RDA levels challenging if you:

• Have had gastric bypass or any gastrointestinal disorder that may hinder calcium absorption.
• Consume high levels of sodium and/or protein, as this may cause more calcium excretion.
• Are taking certain medications like corticosteroids.
• Vegans, lactose intolerant, or those who do not consume dairy.

In these scenarios, calcium supplements might help you meet your calcium goals.

Calcium absorption

Different kinds of calcium compounds contain different amounts of elemental calcium. Elemental calcium is important because it refers to what the body can use for bone growth and other important health functions. However, it is important to note that elemental calcium does not always represent bioavailability or how much calcium will actually be absorbed.

Here are some common calcium supplements and their corresponding elemental calcium amounts:

• Calcium carbonate (40% elemental calcium)
• Calcium lysinate (30% elemental calcium)
• Calcium citrate (21% elemental calcium)
• Calcium lactate (13% elemental calcium)

A study conducted in the Journal of Orthopedic Case Reports found that “calcium lysinate was clearly superior to both calcium carbonate and [calcium citrate] in the ability to deliver calcium to the bloodstream after oral administration, and calcium lysinate may offer significant advantages as a dietary calcium supplement.”

Because calcium can interact with some medications and affect some health conditions, it is important to talk to your doctor or nutritionist before trying calcium supplements.

Calcium is an important mineral for many bodily functions, especially bone integrity, brain health, and heart health. If you have a dairy allergy or choose to avoid dairy, there are other ways you can make sure and consume enough calcium to stay healthy and happy.