Calcium is well known for the role it plays in bone health. However, calcium is a mineral that is necessary for many different physiological functions. Calcium is not only a component of bones and teeth, but it also plays essential roles as a cell-signaling molecule, mediating nerve transmission, muscle contraction, and blood vessel constriction.

The 2020-2025 Dietary Guidelines for Americans identifies calcium as a nutrient of public health concern because it is under consumed in the American diet, and low intakes are associated with health concerns such as osteoporosis and rickets.₁ Approximately 30 percent of men and 60 percent of women over the age of 19 do not consume the recommended intake of calcium.₁ Calcium can be found in a number of different foods including dairy products such as milk, yogurt, and cheese, as well as sardines, salmon, kale, broccoli, and bok choy. Low intakes of calcium are due to low intakes of these foods, which may often be replaced for plant-based milks (which are not always fortified with calcium). Increasing awareness of lactose intolerance may also steer individuals away from dairy products and toward non-dairy alternatives, especially as these alternatives become more palatable and widely available.

The Recommended Daily Allowance (RDA) for calcium is as follows:

• Children ages 1-3: 700 mg
• Children ages 4-8: 1,000 mg
• Children ages 9-18: 1,300 mg
• Adults ages 19-50: 1,000 mg
• Females ages 51-70: 1,200 mg
• Males ages 51-70: 1,000 mg
• Adults >70: 1,200 mg

The RDA for calcium is at its highest during adolescence (9-18 years of age). During this period of growth and development, particularly during pubertal growth spurts, calcium is essential to promote maximal bone formation and bone mass.₂ Additionally, calcium absorption is at its peak during this life stage.₂

The RDA for calcium also increases for females over the of 51 due to the loss of estrogen during menopause. Postmenopausal women have an increased risk of osteoporosis due to decreased estrogen levels that cause resorption (breakdown) of bone and increases in calcium loss.₃ Increasing intake of calcium during this time, as well as vitamin D, is especially important.

99 percent of the body’s calcium is stored in bones and teeth, supporting their structure and function. This makes calcium an essential mineral in the bone remodeling process. The human body is constantly undergoing a continued process of breaking down old bone and forming new. This process is called bone remodeling and is very tightly regulated by signaling molecules and hormones to maintain bone homeostasis. The regulation of bone remodeling allows the body to maintain sufficient levels of serum calcium that are required for physiological processes.₂ During the breakdown of old bone, calcium is released and reabsorbed by the kidneys. During bone formation, calcium is deposited into new bone.₂ Calcium makes up a large portion of the mineral compartment in bone and is part of the compound mineral hydroxyapatite, which is critical for bone structure and necessary for tissue rigidity, strength, and elasticity.₂ Other vitamins and minerals essential to the bone remodeling process include phosphorous and vitamin D.

Certain diets, medications, and diseases can lead to calcium deficiency. Individuals following vegan diets and dairy-free diets may be more prone to low calcium intake. Other factors that can lead to calcium deficiency are long-term intake of corticosteroids and certain bowel or digestive diseases that decrease the ability for the body to absorb calcium, such as inflammatory bowel disease or celiac disease. In these cases, it may be beneficial to supplement with calcium.

Calcium supplements come in many different forms. Each form contains different calcium compounds that have varying concentrations of elemental calcium. For example, some common forms of calcium supplements are calcium carbonate, calcium citrate, and calcium lactate. Calcium carbonate is the most highly concentrated form, containing approximately 40 percent elemental calcium, while calcium citrate and lactate contain around 21 percent and 13 percent elemental calcium, respectively.₄ Calcium carbonate tends to have more adverse effects associated with intake, such as constipation and gastrointestinal discomfort.₄

The absorption of calcium depends on the amount taken. As the amount consumed increases, absorption by the body decreases.₄ To maintain good absorption, calcium should be taken in low doses of 500mg or less at one time.₄ Other vitamins, minerals, and compounds in food also effect absorption of calcium. Vitamin D aids in the absorption of calcium, while oxalates and phytates found in vegetables like spinach and legumes decrease the absorption of calcium. This is important to take into consideration when low calcium levels are a concern.

Calcium is essential for many physiological functions in the body, particularly skeletal health, making it particularly important during childhood growth and development and as the body ages. Consuming enough of this key mineral, whether through diet or supplementation, is important for optimal health.