Highlights

• Calcium is the most abundant mineral in the body. It’s essential for bone health and proper functioning of the cardiovascular, muscular and nervous systems, among many other important roles.
• Only one percent of all body calcium is found in circulation in our bodies, while 99 percent is stored in our bones. Stores of calcium are released from our bones when more is needed.
• The human body does not contain enough calcium for functioning on its own, so obtaining calcium through our diets is an essential part of nutrition and healthy eating.
• Vitamin D helps with calcium absorption and retention.

The basics of calcium

Calcium is the most abundant mineral found in our bodies and performs many vital roles. It is necessary for bone health, cardiovascular and muscle function, and nervous system signaling. Calcium also acts as a coenzyme for many metabolic processes in the body. Calcium is often most closely associated with the skeletal system, as it is critical for developing and maintaining bone structure and function. Ninety-nine percent of all the calcium in our body is stored within our bones, which act as a reservoir for calcium, releasing more of the mineral when it is needed. Only one percent of body calcium is found outside of the skeletal system; this amount is regulated and kept consistent by the body and does not fluctuate with changes in calcium intake.

Our bodies are unable to produce calcium on their own, so we need to obtain the additional calcium our bodies need through our diets. Calcium-rich food sources include dairy products, green cruciferous vegetables and fortified foods such as juices and cereals. Calcium is also available as a dietary supplement. Vitamin D plays a significant role in absorbing calcium from the gastrointestinal tract, so it is important to have adequate amounts of both nutrients to support optimal health.

Calcium and health

Bone Health

One of the most important roles of calcium is assisting with bone development, growth, maintenance and overall structure. Peak bone mass is achieved around the age of 30, at which point bone density is gradually lost due to a continued need for stored calcium for body functions. People who do not consume an adequate amount of calcium before they reach their peak bone mass are at a higher risk of later developing osteoporosis—a disease characterized by low bone density and quality—due to smaller calcium reserves.

There are several risk factors for developing osteoporosis: being female, white or of Asian descent; having a small body frame; age, smoking and drinking excessively; and having a family history of osteoporosis. Postmenopausal women are at particularly high risk for osteoporosis, since they have increased calcium loss due to changes in estrogen levels after menopause. Low calcium intake, being below the recommended body weight for height, being inactive, lactose intolerance and having certain gastrointestinal conditions that interfere with calcium absorption also contribute to osteoporosis risk.

Cardiovascular and Muscular Health

Calcium is essential for proper muscle contraction, including the beating of the heart. Its presence acts as a signal for the muscle fibers to enable the contraction cycle when a muscle is stimulated. Calcium is also involved in blood clotting, by acting as a cofactor for several enzymes involved in the cascade of events needed to begin and maintain the clotting process. Additionally, calcium is responsible for the dilation and contraction of blood vessels.

Other Physiological Functions

Through its actions as a messenger between cells and tissues, calcium is involved in the transmission of nerve signals throughout the body. It also plays a role in hormone secretion.

Recommended intakes

The recommended dietary allowance (RDA) for calcium increases throughout the lifespan until adulthood is reached, when the RDA for both males and females is 1,000 milligrams per day. There are certain demographics and life stages for which the body requires higher levels of calcium: adolescents, who are building bone mass; women over 50 who experience bone loss after menopause; and the elderly, who experience a higher rate of bone loss compared with younger adults.

The Health and Medicine Division of the National Academies of Sciences, Engineering and Medicine have set Recommended Dietary Allowances (RDAs) for calcium:

Recommended dietary allowances (RDAs) for calcium (milligrams (mg)/day)

*Adequate intake

Source: The Health and Medicine Division of the National Academies of Sciences, Engineering and Medicine

Vitamin D is critical in ensuring adequate absorption of calcium from the gastrointestinal tract. Therefore, to ensure adequate calcium intake, it is also important to get enough vitamin D through diet, sun exposure and dietary supplements if needed. The RDAs for vitamin D are 400 international units (IU) for infants ages 0­–12 months, 600 IU for ages 1–70 years, and 800 IU for adults over age 70.

Tolerable upper intake levels (ULs) have also been established for calcium, because it is possible to consume too much of this mineral. This is most common in people who take calcium supplements and is rare in people who consume large quantities of calcium-containing foods. Too-high calcium intake can cause constipation and more serious conditions in the kidney, like kidney stones.

Tolerable upper intake levels (ULs) for calcium (mg/day)

Source: The Health and Medicine Division of the National Academies of Sciences, Engineering and Medicine

Sources of calcium

Dairy foods like milk, cheese and yogurt are the major food contributors to calcium intake in the United States. Calcium is found in non-dairy sources such as dark leafy greens (except spinach, which is high in a compound that binds to calcium and prevents its absorption), soy beans and soy products made with calcium, some types of nuts and seeds and many fortified foods. Calcium is also a component in certain medications in the form of calcium citrate or calcium carbonate, commonly found in over-the-counter antacids.

Calcium is a commonly consumed dietary supplement, but there is limited evidence to support the benefit of calcium supplementation when it comes to preventing bone fractures. The United States Preventive Services Task Force has concluded that there is insufficient evidence to determine the benefit or harm of calcium and vitamin D supplementation in men and premenopausal women. For postmenopausal women living independently, they concluded that there is no benefit to supplementing with doses lower than 1,000 mg/day of calcium and 400 IU/day of vitamin D, and there is insufficient evidence to assess other benefits and harms.

If a person chooses to take calcium supplements, the recommended dose is less than 500 mg, since very little calcium is absorbed above this amount at any one time. This means that if a person hopes to achieve the RDA of calcium from supplements, the supplements should be taken in two separate doses. Similarly, spacing out calcium intake from foods throughout the day will enhance its absorption, as opposed to consuming a lot of calcium-rich foods at the same time.

Sources of calcium

Table Source: U.S. Department of Agriculture, Agricultural Research Service. FoodData Central, 2019. Accessed July 17, 2019.

This article is written by Allison Webster, PhD, RD, with contributions from IFIC intern, Yasaman Salahmand