What is calcium?

Calcium is a mineral that is important for bone health and plays a role in many other body systems.


Calcium is a grayish-white mineral found in nature in varying forms, often in forms referred to as salts. Calcium is an essential nutrient for every cell in the human body, although the largest quantities are found in the bones and teeth. The most common forms of dietary calcium (from food or supplements) are calcium carbonate and calcium citrate, although other forms, such as calcium malate and calcium hydroxyapatite (bone meal), are also used in supplements.

What are the dietary sources of calcium?

Dairy products, including milk, yogurt and cheese, are the richest sources of dietary calcium. Vegetable sources such as bok choy, kale, turnip greens and broccoli contain calcium. Fortified juices and cereals can increase dietary calcium intake. Although spinach contains a large quantity of calcium, it is not easily absorbed because it binds to a compound in spinach called oxalic acid, which prevents its absorption.

Should I consider taking a calcium supplement?

Research suggests that, for a large proportion of the population, diet alone does not supply adequate calcium. Taking a calcium supplement can help ensure that your cells and bones get the calcium they need.

You might not be getting enough calcium from your diet if you are lactose intolerant, have a milk allergy, have been taking certain medications or follow a dairy-free, vegan diet. A number of diseases also can cause you to need more (or less) calcium than normal.

In addition to getting enough calcium, you can take steps to help your body absorb and store calcium more efficiently. These steps include taking a vitamin D supplement and engaging in regular, weight-bearing exercise.

How can calcium affect my health?

Many people are aware that calcium helps build healthy bones and teeth, but did you know that it plays an important role in many other body systems as well? Calcium intake can support your health in several ways:

  • Helps achieve and maintain healthy bone mass*
  • Reduces the risk of osteoporosis later in life*
  • Supports strong teeth*
  • Helps maintain healthy blood pressure*
  • Promotes healthy mucus membranes in the colon*
  • Contributes to normal muscle contraction in skeletal muscle, the heart and blood vessels*
  • Provides support for women with PMS*
  • When taken with magnesium, it helps lower the risk of metabolic syndrome in women*
  • Transmits signals within and between cells, including nerve impulses to the heart*

Calcium is one of the most important nutrients for bone health.* It can help maximize the amount of bone mass you develop, which peaks at about age 30. In turn, this helps offset the loss of bone mass that occurs with aging, especially the rapid loss typically associated with menopause. If you lose too much bone, you can develop osteoporosis, a disease that causes bones to become weak, brittle and prone to fracture. Although osteoporosis is often thought of as a women's health issue, men also lose bone mass as they age and can get osteoporosis.

Although the chance of developing osteoporosis increases as a person ages, the condition can also affect younger people. Athletes can develop osteoporosis at any age, particularly when they don't consume enough nutrients and calories to meet the demands of their training and competition routines. This is especially prevalent in female athletes, who are at risk of a cluster of related conditions called the female athlete triad — the lack of adequate calories and nutrition (often due to eating disorders), menstrual irregularities (such as missing periods or not having periods), and weak bones. Increasing calcium intake as part of restoring a healthy diet and exercise program could help with recovery and help to restore lost bone mass.*

How much calcium should I take?

How much calcium you likely need depends on your age and gender. The FDA's Recommended Dietary Allowance (RDA) is roughly the amount you should try to get every day. The Tolerable Upper Intake Level (UL) is the maximum amount in any given day, from both food and supplements, that most people can take without experiencing harmful side effects.

Age (years) RDA (mg/day) UL (mg/day)
1-3 700 2,500
4-8 1,000 2,500
9-18 1,300 3,000
19-50 1,000 2,500
51-70 1,000 males
1,200 females
+70+ 1,200 2,000

Think about spreading out your calcium intake over the whole day. Studies have shown that taking more than 500 milligrams (mg) of calcium at one time isn't effective, because the body can't efficiently absorb that much calcium all at once. So, for example, if you have milk on fortified cereal at breakfast, save your calcium supplement for later in the day when there's likely less calcium in your food.

Also, the type of calcium you eat or take can affect your body's ability to absorb it. Calcium carbonate is better absorbed as part of a meal, while calcium citrate, calcium malate and calcium citrate-malate are well-absorbed with or without food.

Many factors affect how well your body can absorb calcium from any source, whether food or supplement, and how effectively your body uses it. These factors include:

  • Some diseases and conditions; for example, kidney disease can prevent the kidneys from activating vitamin D, which can lead to poor calcium absorption. Digestive conditions that result in poor nutrient absorption, such as celiac disease or Crohn's disease, can also negatively affect calcium absorption.
  • Certain medications (see below).
  • Quantity of stomach acid.
  • Exercise.
  • Levels of other nutrients in your body. Experts recommend taking vitamin D along with calcium because vitamin D plays a key role in helping the body absorb calcium. Vitamin K and magnesium are two other nutrients that also are important for calcium metabolism and bone health.*

Are there any side effects from taking a calcium supplement?

Consuming too little calcium tends to be a more common health concern than consuming too much, but it is possible to have too much of a good thing. Some researchers have raised a concern about the potential risk of heart disease from excessive calcium supplementation. However, the American Society for Preventive Cardiology notes that dietary and supplemental calcium are safe for cardiovascular health when consumed in recommended amounts.* Many nutrition experts suggest taking magnesium along with calcium to keep calcium in the bone and out of soft tissues such as arteries.*

When consumed as a combination of food and supplements in the recommended dose range according to age, calcium is considered safe for most healthy adults and children. Taking higher amounts (but below the upper limit guidelines) has limited additional benefit and would be more likely to cause side effects such as constipation, indigestion and other gastrointestinal discomfort.

Is supplemental calcium safe to take with medications?

Oral calcium supplements can interfere with the absorption of some prescription medications, including bisphosphonates, quinolone antibiotics, tetracycline and levothyroxine (Synthroid®). You can avoid or minimize these effects by taking the medication at a different time of day than you take a calcium supplement.

Antacids such as H2-blockers or proton pump inhibitors can interfere with calcium absorption. Other medications can interfere with calcium metabolism. For example, glucocorticoids such as prednisone can cause the loss of more calcium than normal, while thiazide-type diuretics can cause more calcium to be retained than normal.

If you are considering taking a calcium supplement, check with your health care professional first, especially if you are pregnant or have a health condition.

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.

Dec. 09, 2016