The major minerals calcium, phosphorus, magnesium, and sulfur play essential roles in human health by supporting the structure, regulation, and metabolic activities of the body. Although they are often discussed in relation to bone health, these minerals extend far beyond the skeleton and are critical for daily physiological function.

Sulfur is unique among the major minerals. It is not consumed as a free mineral in foods but is found exclusively as a component of certain amino acids—most notably methionine and cysteine. Through these amino acids, sulfur contributes to protein structure and function but has no independent physiological role outside of its presence in amino acids and the compounds derived from them.

Calcium: More Than Just Bones

When most people think about calcium, they think about strong bones and teeth—and for good reason. More than 99% of the body’s calcium is stored in the skeleton, where it provides structure and strength. The remaining 1% circulates in body fluids and tissues, where it performs critical functions necessary for life.

Calcium helps transmit nerve impulses, supports muscle contraction (including the heartbeat), and plays a key role in blood clotting. Because these functions are essential, the body carefully maintains calcium levels in the blood within a narrow range.

Bone Health

Bone is living tissue that is constantly being broken down and rebuilt. During childhood, adolescence, and early adulthood, bone formation occurs faster than bone breakdown. Adequate calcium intake during these years helps maximize peak bone mass, which may reduce the risk of osteoporosis later in life (Figure 9.6).

When dietary calcium intake remains too low over time, the body may draw calcium from bone to maintain normal blood levels. As a result, bone density gradually declines, increasing the risk of fractures.

Hormonal Regulation of Blood Calcium

Table 9.1 summarizes the major functions of calcium and its potential health benefits.

Groups at Risk for Calcium Deficiency

Many Americans do not consume enough calcium. Young women, older adults, and people who avoid dairy products are especially at risk. Because peak bone mass is built during adolescence and young adulthood, the college years are an important time to establish calcium-rich eating habits.  Despite strong evidence supporting calcium’s benefits—particularly for bone health—most Americans do not meet recommended intake levels. In fact, nearly half of adult women in the United States consume less calcium than recommended, and among women who do not take calcium supplements, approximately 60% have inadequate calcium intakes. ^[1]

Dietary Needs and  Sources of Calcium

Calcium requirements vary across the lifespan. Most adults ages 19–50 need 1,000 mg of calcium per day. Requirements increase for women over age 50 and men over age 70 because bone loss becomes more common with aging, as outlined in Table 9.2.

In the United States, dairy products such as milk, yogurt, and cheese are the primary sources of calcium. One cup of milk provides about 300 mg of calcium, while a slice of cheddar or Swiss cheese provides about 200 mg.

Calcium is also added to many fortified foods, including breakfast cereals, plant-based beverages, and some orange juices. In addition, many naturally calcium-rich non-dairy foods make it possible to meet calcium needs through vegetarian and vegan eating patterns. Examples of calcium-rich foods are shown in Figure 9.8.

Calcium Supplements: Which One to Buy?

Many people use calcium supplements when they are unable to meet their needs through food alone. The most common forms are calcium carbonate and calcium citrate.

• Calcium carbonate is inexpensive and contains a large amount of calcium, but it is absorbed best when taken with food because it requires stomach acid for absorption.
• Calcium citrate is absorbed well with or without food and may be a better choice for older adults and individuals who take acid-reducing medications.

Most experts recommend obtaining calcium from foods whenever possible because foods provide additional nutrients that support bone health.

Consumer Tip: Not All Supplements Are Equal

Some calcium supplements derived from natural sources, such as oyster shell, bone meal, or dolomite, may contain trace amounts of lead or other contaminants. Choosing products that have been independently tested by reputable third-party organizations can help ensure quality and purity.

Remember, “natural” does not always mean safer. Whenever possible, focus on meeting calcium needs through foods such as dairy products, fortified beverages, tofu, and leafy green vegetables.

Phosphorus: Where Energy Meets Structure

Although phosphorus is often associated with healthy bones and teeth, its most important jobs occur inside every cell of the body. Phosphorus is found in phosphate groups, which are essential components of DNA and RNA, cell membranes (phospholipids), and ATP, the body’s primary energy molecule. Every heartbeat, muscle contraction, nerve impulse, and chemical reaction that requires energy depends on phosphate. About 85% of the body’s phosphorus is stored in bones and teeth, where it works together with calcium to provide strength and structure.

Unlike calcium, phosphorus deficiency is uncommon because phosphorus is found naturally in many protein-rich foods, including meat, poultry, fish, dairy products, nuts, beans, and whole grains. In addition, phosphate is widely used as a food additive in processed foods. It helps prevent clumping, improves texture, enhances flavor, and extends shelf life. Processed meats, frozen convenience foods, processed cheeses, baked goods, and many cola soft drinks contain added phosphates.

In fact, early cola beverages were once called “phosphates” because they contained phosphoric acid, which gave the drinks a tart flavor. Today, cola soft drinks remain one of the largest sources of added phosphorus in the American diet.

Dietary Needs  and Sources of Phosphorus

Because phosphorus is so common in foods and food additives, most Americans consume far more than the Recommended Dietary Allowance (RDA) of 700 mg per day. Average daily intake ranges from 1,000 to 1,500 mg, with much of the excess coming from highly processed foods. While healthy kidneys remove excess phosphorus from the blood, people with chronic kidney disease or those receiving dialysis often must limit foods high in phosphorus because their kidneys cannot remove it efficiently. Excess phosphorus can accumulate in the blood, contributing to bone disease and calcium deposits in blood vessels and other soft tissues.

For most healthy adults, however, phosphorus deficiency is rare, and eating a balanced diet easily provides enough to support energy production, healthy bones, cell membranes, and genetic material.

The figure below includes the phosphorus content of various foods.

Magnesium: Powering Enzymes, Muscles, and Nerves

Although more than half (50–60%) of the body’s magnesium is stored in bones, its most important functions occur throughout the body. Magnesium is required for more than 300 enzyme reactions involved in producing energy, building proteins, and synthesizing DNA and RNA. It is also essential for normal nerve transmission, muscle contraction, and every reaction involving ATP, the body’s primary energy molecule.

Magnesium also supports healthy bones by helping regulate parathyroid hormone (PTH) and vitamin D, two key regulators of calcium balance. Research suggests that people who consume adequate magnesium tend to have better bone mineral density and a lower risk of osteoporosis, although more research is needed to determine whether magnesium supplements provide additional benefits.National Institutes of Health Office of Dietary Supplements. Magnesium: Fact Sheet for Health Professionals. Updated January 6, 2026. Accessed June 16, 2026. https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/[/footnote]

Many Americans do not consume enough magnesium. Long-term inadequate intake has been associated with an increased risk of osteoporosis and cardiovascular disease. Although severe magnesium deficiency is uncommon, symptoms may include loss of appetite, nausea, muscle spasms, tremors, and abnormal heart rhythms.

Dietary Needs  and  Sources for Magnesium

The Recommended Dietary Allowance (RDA) for magnesium is 400 mg/day for men and 310 mg/day for women ages 19–30. After age 30, magnesium needs increase slightly.

Magnesium is a component of chlorophyll, the green pigment that enables plants to carry out photosynthesis. As a result, green leafy vegetables such as spinach and kale are among the best dietary sources of magnesium. Other good sources include legumes, nuts, seeds, whole grains, fish, dairy products, and dark chocolate. Coffee and hard water can also contribute small amounts of magnesium.

Because many Western diets contain too few whole grains, legumes, nuts, and leafy green vegetables—and too many refined grains—many Americans do not meet the recommended magnesium intake.

Although calcium, phosphorus, magnesium, and sulfur have different functions, they work together to maintain healthy bones, produce energy, support muscles and nerves, and keep the body functioning normally. Eating a varied diet that includes dairy products or fortified alternatives, whole grains, legumes, nuts, vegetables, and protein-rich foods is the best way to obtain these essential minerals.

Use the table below as a quick reference to review the major functions, food sources, and deficiency symptoms of calcium, phosphorus, magnesium, and sulfur. 

Attributions

This section is an adaptation of "Calcium", "Phosphorus", and "Magnesium" in Human Nutrition: 2020 Edition by University of Hawai‘i at Mānoa Food Science and Human Nutrition Program licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.