The Ins and Outs of Calcium
Written By Kobi Nathan, Pharm.D., M.Ed., CDP, BCGP, AGSF
Sleep Disorders
October 6, 2021

What is calcium and what does it do? What is its relationship to vitamin D?

Calcium is an important mineral that functions to build strong and healthy bones. In fact, around 99% of the body’s calcium is present in our bones and teeth.

Calcium is also involved in blood clotting, muscle contraction, the nervous system, and maintaining our heartbeat. It is an inorganic element not naturally produced by our bodies, so we must get it through the food we eat.

When we are not taking in as much calcium as our body requires, our body will compensate by dipping into the calcium stores in our bones.

With prolonged calcium deficiency, bones become weaker, softer, and are more susceptible to breaking. This can lead to eventual bone loss, decreased bone density, or broken bones.

Vitamin D is another important nutrient in our bodies that works with calcium to protect our bones. Vitamin D aids in the body’s absorption of calcium and protects the muscles to prevent falls.

Vitamin D is important in children so that they can develop strong bones, and adults need vitamin D to maintain healthy and strong bones. The relationship between calcium and vitamin D is important and will be discussed further in this article.

What are the benefits of calcium?

As mentioned above, the body needs calcium to keep your bones strong. Menopausal women in particular tend to lose bone density at a faster rate than males or younger individuals.

Likewise, women are at a higher risk of developing osteoporosis. Patients who have osteoporosis or osteopenia can benefit from adequate calcium intake to prevent falls and broken bones.

Calcium also has a significant role in muscle contraction. When the muscle is stimulated by a nerve, the body produces calcium which aids in muscle contraction.

As calcium is pumped out of the muscle, the muscle will respond by relaxing. This is especially important in controlling action in the heart muscle. Calcium relaxes the muscle surrounding blood vessels, suggesting a potential role in maintenance of blood pressure.

Other studies indicate that calcium, in conjunction with vitamin D, may demonstrate even more benefits. Experts suggest a potential role in preventing cancer and diabetes. However, more studies need to be done to confirm these benefits.

What foods provide calcium? How do I know how much calcium I am getting from my food?

There are many types of food that with regular intake can provide adequate amounts of calcium for our bodies to grow and function. Common calcium sources from your diet may include:

  • Dairy products such as milk, yogurt, and cheese
  • Vegetables such as kale and broccoli
  • Fish with soft bones, like canned salmon and sardines
  • Grains such as pasta, bread, and cereals

If you want to know how much calcium you are getting from your diet, pay attention to the food labels for the daily value (DV). Calcium content will be displayed as a percentage of the DV based on a DV of 1,000 mg. For example:

  • 25% DV of calcium equals 250 mg of calcium
  • 10% DV of calcium equals 100 mg of calcium

How much calcium do you need?

The amount of calcium you need will depend on your age and sex. The recommended daily amounts below include calcium intake from both food and supplements.

Recommended Daily Calcium Intake

Less than or at least 50 years old 1,000 mg daily
Greater than 50 years old 1,200 mg daily
Less than or at least  70 years old 1,000 mg daily
Greater than 70 years old 1,200 mg daily

So, who needs calcium supplements?

Whether or not you need a calcium supplement depends on how much calcium you ingest through your diet. The goal is to achieve the daily recommended amount of calcium only through diet, as there is no benefit to taking more calcium than needed.

Ingesting too much calcium can actually pose some health risks, and therefore is not recommended.

However, some individuals do not receive enough calcium from their food intake and thus will require extra supplementation, such as those with osteoporosis or osteopenia. These individuals should be dosed and monitored by their doctor.

Should calcium be taken with vitamin D?

Osteoporosis affects more than 10 million people over the age of 50 in the United States. Those that are deficient in calcium and vitamin D have a higher risk of having weak bones and developing osteoporosis later in life.

Having brittle bones can lead to breaks and fractures, causing serious injuries. Those that are deficient in vitamin D do not produce sufficient amounts of calcitriol (the “active” form of vitamin D), which leads to decreased calcium absorption from food.

The body will compensate by taking calcium from existing bone stores, thus weakening bones and preventing the formation of new, strong bones. Because calcium and vitamin D work together, it is necessary to have sufficient intake of both to sustain good bone health.

The risk of breaking a bone and falling can be lessened by taking calcium and vitamin D supplements together. You should only take these supplements if they are prescribed by your doctor to treat osteopenia and osteoporosis.

Typically, if you are prescribed calcium, adding vitamin D to your regimen will help increase absorption of calcium for maximal effects.

Taking an appropriate daily dose of vitamin D is likely to get your levels within the desired range without needing to do blood tests. A daily dose of vitamin D should not exceed 1,000-2,000 international units (IU) daily.

Doses higher than this may carry some risks, and one study demonstrated an increased incidence of falls and fractures in older adults who were on high doses of vitamin D (>500,000 IU per year).

Only take doses higher than 2,000 IU if prescribed and monitored by a doctor.

Types of calcium supplements

There are a few types of calcium supplements that contain different amounts of elemental calcium. Elemental calcium represents the actual amount of calcium contained in the supplement. Some examples of types of calcium supplements include:

  • Calcium carbonate (40% elemental calcium)
  • Calcium citrate (21% elemental calcium)
  • Calcium lactate (13% elemental calcium)
  • Calcium gluconate (9% elemental calcium)

Calcium citrate and calcium carbonate are the two major types of calcium supplements. Calcium carbonate is the least expensive and thus usually an appropriate first choice.

When choosing which supplement to use, consider factors such as the amount of elemental calcium, side effects, cost, and what other medicines you take.

Supplements can interact with certain other medications, such as blood pressure medications and antibiotics. Make sure your doctor is aware of all other medications you take.

Ask about the best way to take your calcium to avoid it interacting with your other medications.

How can calcium interact with other medications or supplements?

Calcium supplements could potentially interact with medications that you take. For example, certain drugs can either increase or decrease the calcium levels in the body.

Make sure to always tell your provider or pharmacist any supplements you take in addition to your prescribed medications. They will alert you if calcium interacts with your medications and how to manage it.

For reference, some examples of medications that could interfere with calcium are listed below.

  • Calcium can decrease the absorption of:
    • Bisphosphonates (treat osteoporosis)
    • Certain antibiotics
    • Levothyroxine (treats thyroid conditions)
    • Phenytoin (an anticonvulsant)
  • Can decrease calcium levels in the blood
    • Diuretics (“water pills”)
    • Certain antacids
    • Certain steroids (such as prednisone)
  • Can increase calcium levels in the blood
    • Diuretics

What is important to know about calcium supplements?

Calcium is an over-the-counter medication that is available without a prescription. There are many different forms and types of calcium that contain varying amounts of the supplement.

Choosing the most appropriate type of calcium will depend on your specific needs such as cost, availability, and convenience. When picking a supplement, there are a few important points to remember:

  • Read the supplement label carefully. Pay close attention to the amount of elemental calcium in the supplement. This amount refers to the actual dose of calcium that is included in the supplement. Knowing this information will help you determine how many pills to take.
  • Pick a trusted supplement brand. Supplements that have been tested and meet current standards for purity and quality by the United States Pharmacopeia (USP) will have a “USP Verified Mark” on the label. Not all supplements will have this label.
  • Take your calcium supplement with food. When you have a meal, your stomach makes acid that aids in the absorption of most calcium supplements. This is true for most calcium supplements, except for calcium citrate which can be taken without regard to food.
  • Be aware of side effects. Calcium supplements can cause gas or constipation. To help prevent these effects, try increasing your fluid intake. If side effects persist, consider switching to a different type of calcium.


For certain patients, supplementation with calcium can be beneficial in preventing falls and broken bones. Patients who have osteopenia or osteoporosis should be on calcium in combination with vitamin D to prevent such adverse events.

Calcium and vitamin D should only be taken if prescribed and monitored by a doctor.



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