Calcium supplements are calcium compounds manufactured in a variety of forms, including tablets, capsules, chews, liquids, and powders.

For adults, the Reference Daily Intake (RDI) of calcium is 1,000 milligrams (mg) daily, which increases to 1,200 mg per day for women over age 50 and men over age 70.

Adults between the age of 19 and 50 years should not get more than 2,500 mg of calcium total per day from all sources including food and supplements. Adults over the age of 50 years should not exceed 2,000 mg total per day.

Your doctor will recommend you calcium supplements if you are not getting enough of it from food and your body lacks it. They are usual for preventing and treating osteoporosis and its predecessor, osteopenia.

Over-supplementation can be harmful, so be sure not to exceed the established tolerable upper intake level (UL), which is 2,500 mg a day for adults aged 19 to 50 years. For those 51 and older, the UL is 2,000 mg a day.

Do not self-medicate on these supplements because overuse can lead to high levels of calcium in the blood. High levels are referred to as hypercalcemia and further calcium toxicity.

Too much calcium in your blood can make your bones weak, can encourage the formation of kidney stones, and interfere with the function of your heart and brain.

Types of calcium supplements

Forms of calcium include:

Calcium carbonate

Calcium carbonate is an over-the-counter inorganic salt mainly used in the treatment of low calcium conditions, gastroesophageal reflux disease (GERD), chronic kidney disease (CKD), and some other conditions.

It is classified as a calcium supplement, antacid, and phosphate binder. These supplements of calcium do not cost much and each oral or chewable tablet contains 40% elemental calcium and provides 200 mg or more of calcium. For its proper absorption, this form of calcium should be taken with meals.

Some well-known calcium carbonate supplements include Caltrate, Viactiv Calcium Chews, Os-Cal, and Tums

Calcium citrate

Each tablet of calcium citrate contains 21% elemental calcium and is a more expensive form of calcium. It is best absorbed both on an empty or full stomach. Older people who have low levels of gastric acid and those who suffer from inflammatory bowel disease or absorption disorders are advised calcium citrate.

Calcium citrate products include Citracal and GNC Calcimate Plus 800.

Other forms

Other supplements include calcium gluconate (9% elemental calcium), calcium lactate (13% elemental calcium), and calcium phosphate. Their calcium content is less than the carbonate and citrate forms and do not offer any advantages.

In addition, some calcium supplements come combined with vitamins and other minerals. For example, many calcium supplements come with vitamin D and/or magnesium. This makes such supplements ideal for people with bone loss.

Which form of calcium is best

Calcium carbonate supplements tend to be the best for their value since they contain the highest amount of elemental calcium.

Most people tolerate calcium carbonate well, but some may experience mild constipation or a feeling of fullness in the abdomen.

Calcium citrate supplements, on the other hand, are more well-absorbed than calcium carbonate. They can comfortably be taken on an empty stomach.

However, since their calcium content is low, only 21% elemental calcium, you may need to take more than one tablet to meet your daily requirement.

Oral supplements are used to prevent and treat low calcium blood levels, osteopenia, osteoporosis, and rickets. Intravenous calcium supplements (calcium chloride and calcium gluconate) are used when low calcium levels result in muscle spasms, high serum potassium, and magnesium toxicity.

Take calcium in smaller doses (less than 600 milligrams at one time) because it is best absorbed this way. Any extra intake will be excreted in your urine. If you take 1,000 mg of calcium a day, split it into two or more doses throughout the day.

Secondly, avoid taking calcium supplements with very high-fiber meals. Fiber can bind with calcium, reducing the amount available to your body for absorption.

Calcium supplements can be taken at any time during the day. You can take calcium citrate with or without food. However, calcium carbonate should be taken with food because the stomach acid produced during meals helps your body absorb calcium carbonate better.

Who should consider calcium supplements?

Getting enough calcium is essential primarily for strong bones and teeth. Calcium supplements, besides other reasons, are given to people with osteoporosis – a condition in which the bones become weak and fragile and very prone to fractures.

Women especially after menopause are prone to this condition. Eighty percent of the 10 million Americans who suffer from osteoporosis are women.

The following conditions may require you to take calcium supplements:

If you

  • Follow a vegan diet
  • Have lactose intolerance and cannot consume dairy products
  • Consume large amounts of protein or sodium, which can excessive excretion of calcium from your body
  • Are on long-term corticosteroid therapy
  • Have certain bowel or digestive diseases such as inflammatory bowel disease, celiac disease, or Crohn’s disease that do not allow proper absorption of calcium
  • Are pregnant or lactating

Do calcium supplements have risks?

Calcium supplements may cause side effects. They include constipation, severe diarrhea, and abdominal pain. Calcium carbonate is more often associated with gastrointestinal side effects, including constipation, flatulence, and bloating.

Taking too much calcium can cause high calcium levels in the blood. This is called hypercalcemia. Too much calcium in your blood can weaken your bones, create kidney stones, and interfere with the function of the heart and brain.

There is another controversial claim that hypercalcemia may increase the risk of prostate cancer.

When you should not take calcium supplements?

You should not take calcium supplements if you have health conditions that cause hypercalcemia and take medications that can increase calcium levels in the blood. Such health conditions include:

Certain medications that can increase blood calcium levels include:

  • Hydrochlorothiazide and other thiazide diuretics
  • Lithium
  • Excessive intake of vitamin D and vitamin A supplements

Possible interactions with calcium

Calcium supplements can interact with other medicines. A drug interaction can adversely affect how a drug works. Supplements have the potential to interact with prescribed medications.

Risk factors for drug interactions include:

  • the use of multiple medications or supplements
  • old age
  • inadequate kidney or liver function, and
  • use of medications that have small differences between their therapeutic and toxic doses (Narrow therapeutic index)

Calcium supplements can interact with many different prescription medications. They include:

  • Blood pressure medications
  • Synthetic thyroid hormones, levothyroxine
  • Bisphosphonates given for osteoporosis
  • Tetracycline antibiotics (such as doxycycline, and minocycline)
  • Fluoroquinolones, and calcium channel blockers.
  • Some diuretics. Taking large amounts of calcium with thiazide diuretics — such as chlorothiazide (Diuril), hydrochlorothiazide (Microzide) and indapamide — can increase the risk of milk-alkali syndrome, a serious condition.
  • Loop diuretics increase the excretion of calcium leading to its increased loss from the body
  • Corticosteroids decrease the absorption of calcium, which can lead to osteoporosis.
  • Calcium carbonate can reduce the bioavailability of ciprofloxacin by 40%, which could result in uncontrolled infection
  • Vitamin D promotes calcium absorption. Therefore, drugs that speed up the body’s normal breakdown of vitamin D such as phenytoin, phenobarbital, and orlistat, may decrease the amount of calcium absorbed from the diet.

Ideally, a minimum of two hours is usually advised with some experts citing four to six hours as a minimum time difference between taking two medications.