Although trace minerals are needed in small amounts, their impact on human health is anything but small. Trace minerals play essential roles in growth, metabolism, immune function, oxygen transport, and hormone production, and even mild deficiencies can lead to significant health consequences. Among the many trace minerals required by the body, iron, zinc, copper, and iodine are especially important because of their widespread involvement in vital physiological processes and their relevance to public health nutrition.  Information from this section is taken from the NIH Supplement Vitamin and Mineral Fact Sheets.

Unlike macronutrients, trace minerals are required in milligram or microgram amounts, but this does not mean they are easy to obtain. Dietary intake, food choices, soil content, food processing, and physiological needs all influence trace mineral status. Certain populations—including pregnant individuals, infants, adolescents, older adults, and those following restrictive diets—may be at increased risk for deficiency.

This section explores the functions, dietary sources, deficiency symptoms, toxicity risks, and public health significance of iron, zinc, copper, iodine, and fluoride. Understanding these trace minerals provides a foundation for recognizing how small nutrients play a big role in maintaining health across the life span.

Iron: Essential for Healthy blood and Energy

Iron is a trace mineral essential to life that plays critical roles in oxygen transport, energy metabolism, immune function, and brain development. Many of iron’s functions are linked to its role in maintaining healthy blood and ensuring that oxygen is efficiently delivered to body tissues.^[1]

One of iron’s primary functions is as a component of hemoglobin, the protein in red blood cells responsible for transporting oxygen. Iron-containing heme groups bind oxygen in the lungs and release it to cells throughout the body (Figure 9.13). This oxygen delivery is essential for normal metabolism and energy production. Iron is also a component of myoglobin, a related protein in muscle cells that stores and supplies oxygen during physical activity.

Blood: Transporter of Oxygen

Blood is a specialized connective tissue that transports oxygen, nutrients, hormones, and metabolic waste products throughout the body. It is composed of several key components: red blood cells, which carry oxygen; white blood cells, which support immune defense; platelets, which assist with blood clotting; and plasma, the fluid medium that transports cells and dissolved substances. Because blood cells—especially red blood cells—are continuously broken down and replaced, a steady supply of iron is essential to maintain normal hemoglobin levels.

Iron, Hemoglobin, and Oxygen Delivery

Iron plays a central role in oxygen transport as a component of hemoglobin, the protein in red blood cells that binds oxygen in the lungs and releases it to tissues. When iron intake or body iron stores are insufficient, hemoglobin production declines. As a result, fewer red blood cells are produced, and those that are formed are smaller and contain less hemoglobin. This condition, known as iron-deficiency anemia, reduces the blood’s capacity to deliver oxygen to tissues.

In addition to its role in hemoglobin, iron is required for several enzymes involved in mitochondrial energy production. Low iron status, therefore, limits both oxygen delivery and cellular ATP production.

Symptoms of Iron Deficiency: Low Iron, Low Energy

Together, impaired oxygen transport and reduced energy production explain why fatigue, weakness, reduced endurance, and difficulty concentrating are among the earliest and most common symptoms of iron deficiency. These symptoms often appear before anemia becomes severe and can negatively affect physical performance and academic functioning.

Populations at Highest Risk of Deficiency

Iron deficiency is the most common nutrient deficiency worldwide and the leading cause of anemia. Certain groups are at higher risk due to increased iron needs or losses:

• Infants and young children, especially those born prematurely, with low birth weight, or to iron-deficient mothers, may begin life with limited iron stores during a period of rapid growth.

• Adolescents, particularly girls, have increased iron needs due to growth and menstrual blood loss, often combined with low dietary iron intake. In these groups, iron deficiency may impair growth, attention, and school performance and, in severe cases, lead to pica—cravings for non-food items such as ice, dirt, or clay.

• Women of reproductive age require more iron due to menstrual blood loss, and this need increases further during pregnancy to support fetal growth and an expanded blood volume. These higher requirements are reflected in the RDA and help explain why meeting iron needs through diet alone can be challenging. For example, a 3-ounce serving of beef provides only about 3 mg of iron, a modest contribution toward many women’s daily iron needs.

Food Sources of Iron

There are two types of iron found in foods: heme iron and non-heme iron.

• Heme iron is iron that is part of the proteins hemoglobin and myoglobin, so it is found only in animal foods such as meat, poultry, and fish. Because heme iron is already bound within these proteins, it is more readily absorbed by the body and is considered the most bioavailable form of iron.
• Non-heme iron is iron that exists as a mineral by itself and is not part of hemoglobin or myoglobin. It is found in both plant foods (such as beans, lentils, nuts, vegetables, and whole or fortified grains) and some animal foods. Non-heme iron is less efficiently absorbed than heme iron, but its absorption can be improved.

Certain foods help increase the absorption of non-heme iron. Vitamin C, as well as meat, poultry, and seafood, can significantly enhance the body’s absorption of non-heme iron. For example, eating an orange or adding tomatoes or bell peppers to a bowl of vegetarian chili can help the body absorb more iron from the beans and vegetables.

How Much Iron Do You Actually Absorb?

Only a fraction of dietary iron is absorbed. On average, 14%–18% of iron is absorbed from mixed diets containing both plant and animal foods, compared with 5%–12% from vegetarian diets. Absorption is influenced by dietary enhancers and inhibitors as well as an individual’s iron status. Because the body has no efficient way to excrete excess iron, iron balance is tightly regulated in the intestine. When iron stores are low, absorption increases to help meet physiological needs.

Iron requirements vary by sex and life stage. Menstruating women have higher iron needs due to monthly blood loss, with an RDA of 18 mg/day, compared with 8 mg/day for adult men. Meeting these higher needs can be difficult, particularly when absorption is limited.

In the United States, the average diet provides about 5–6 mg of iron per 1,000 kilocalories. While this may appear adequate, total iron intake depends on both calorie intake and food quality. Many commonly consumed ultra-processed foods contain added iron through enrichment, but this iron may be less bioavailable—especially when diets are low in vitamin C and high in absorption inhibitors such as phytates. As a result, individuals may consume sufficient calories yet still fall short of meeting iron needs.

Importantly, most of the body’s daily iron requirement does not come directly from food. Instead, approximately 90% of iron is supplied through internal recycling, primarily from the breakdown of older red blood cells. This efficient conservation system helps maintain iron balance, even when dietary intake is modest.

Can You Get Too Much Iron?

The body excretes very little iron, so excess intake—especially from supplements—can lead to iron buildup in tissues and organs. This accumulation can cause serious health problems, including extreme fatigue, joint pain, arthritis, and damage to the liver and heart.

Iron toxicity is particularly dangerous in children. Ingesting as little as 200 mg of iron has resulted in fatal poisoning, which is why iron supplements should always be kept out of reach of children. To help prevent toxicity, the Institute of Medicine has established Tolerable Upper Intake Levels (ULs) for iron at 45 mg/day.

Some individuals are also at risk due to hemochromatosis, a hereditary condition caused by a genetic mutation that disrupts normal iron regulation. In people with hemochromatosis, iron accumulates excessively in organs such as the liver, pancreas, and heart, leading to symptoms similar to iron overload from supplements—but often more severe.  ^[2]

Preventing Iron-Deficiency Anemia

In infants and young children, iron-deficiency anemia can impair motor development, learning, and behavior, with effects that may last long term. In the United States, it was a major public health concern before the 1970s but has declined significantly due to routine screening, iron-fortified formulas and cereals, and programs such as WIC. Additional strategies—breastfeeding, appropriate iron supplementation, and delaying cow’s milk until after 12 months—also contributed to this improvement.

As children transition to solid foods, prevention focuses on offering iron-rich foods paired with vitamin C, limiting cow’s milk to less than 24 ounces per day, and using supplements when needed.

Globally, iron-deficiency anemia remains a serious issue, contributing to about one million deaths each year, especially in Africa and Southeast Asia. Key prevention strategies include iron supplementation, food fortification, malaria prevention, insecticide-treated bed nets, and treatment of intestinal parasites. Researchers are also exploring simple approaches, such as using iron cookware, to increase iron intake in high-risk populations.

Zinc and Copper: Essential Trace Minerals

Zinc and copper are trace minerals needed in small amounts but are critical for growth, metabolism, and overall health. Both minerals act primarily as enzyme cofactors, helping enzymes carry out essential chemical reactions in the body.

Zinc: Growth, Immunity, and Metabolism

Zinc is a cofactor for hundreds of enzymes involved in DNA, RNA, and protein synthesis, as well as energy metabolism. Because of these roles, zinc is essential for normal growth, immune function, wound healing, and taste perception. Zinc deficiency is most concerning during infancy, childhood, and adolescence, when growth demands are high. Inadequate zinc intake can slow growth and delay sexual maturation. This relationship was first identified in the 1960s when adolescent growth failure was observed in populations consuming diets high in phytates, compounds found in whole grains and legumes that reduce zinc absorption. Severe zinc deficiency in adults may cause hair loss, diarrhea, skin lesions, poor appetite, weight loss, and impaired immune function. Zinc is also required for heme synthesis, and prolonged deficiency can contribute to anemia. Globally, zinc deficiency is common, especially in regions where diets rely heavily on cereal grains and contain little red meat or seafood, which are the most bioavailable sources of zinc.^[3]

Copper: Iron Metabolism and Antioxidant Defense

Copper works closely with iron in the body. It assists in electron transfer during energy production and serves as a cofactor for enzymes involved in iron absorption, transport, and mobilization. Without adequate copper, iron cannot be efficiently used to make red blood cells, which may result in anemia, even when iron intake is sufficient. Copper also functions as an antioxidant, helping protect cells from oxidative damage. Severe copper deficiency is rare but may cause anemia, impaired growth in children, and neurological problems. These neurological effects occur because copper is needed for enzymes involved in myelin formation, the protective covering around nerves.

Dietary Considerations for Zinc and Copper

Zinc is widely available in foods, with the richest sources being oysters, red meat, pork, and seafood, followed by beans, dairy products, nuts, and whole grains. However, zinc from plant foods is less well absorbed due to phytates. Copper is found in a variety of foods, including organ meats, shellfish, nuts, seeds, whole grains, and legumes. Together, zinc and copper illustrate how trace minerals—though needed in small amounts—play outsized roles in growth, energy metabolism, blood health, and nervous system function.

Copper, like iron, assists in electron transfer in the electron-transport chain. Furthermore, copper is a cofactor of enzymes essential for iron absorption and transport. The other important function of copper is as an antioxidant. Symptoms of mild to moderate copper deficiency are rare. More severe anemia can cause anemia due to the lack of iron mobilization in the body for red blood cell synthesis. Other signs and symptoms include growth retardation in children and neurological problems, because copper is a cofactor for an enzyme involved in myelin synthesis, which surrounds many nerves.

Dietary Sources of Zinc

Selenium: Thyroid Function and Antioxidant Protection

Selenium is a trace mineral best known for its roles in thyroid hormone regulation and antioxidant defense. Inside cells, selenium is required to convert inactive thyroid hormone into its active form. For this reason, selenium deficiency can produce symptoms similar to iodine deficiency, such as fatigue and slowed metabolism.^[5]

Selenium is also a key component of the body’s antioxidant system. About two dozen selenium-containing proteins help protect cells from oxidative damage. Some of the most important—glutathione peroxidases and thioredoxin reductase—neutralize free radicals and help regenerate other antioxidants, including vitamin C and vitamin E. This teamwork highlights how antioxidants work together rather than in isolation.

Because selenium protects fats and cell membranes from oxidative damage, it has been studied for its potential role in preventing cancer and cardiovascular disease. Observational studies suggest that low selenium status is associated with higher cancer risk, but clinical trials have not shown clear benefits from selenium supplements. Similarly, evidence linking selenium to reduced heart disease risk remains inconsistent. These findings reinforce an important nutrition principle: more is not always better, especially when it comes to supplements.

Intake, Safety, and Food Sources of Selenium

The Recommended Dietary Allowance (RDA) for selenium in adults is 55 micrograms per day, an amount needed to maximize antioxidant enzyme activity. While selenium from foods is generally safe, excess intake from supplements can be toxic. Chronic high intakes may cause brittle hair and nails, digestive upset, fatigue, irritability, and a garlic-like breath odor. For this reason, the Tolerable Upper Intake Level (UL) for adults is 400 micrograms per day.

Selenium is found primarily in animal-based foods, including seafood, meats, poultry, eggs, and dairy products. Plant foods contain selenium only if they are grown in selenium-rich soil. Brazil nuts are an especially concentrated source—so much so that just one or two nuts can meet or exceed daily needs.

Key takeaway: Selenium is essential for thyroid health and antioxidant protection, but balance matters—adequate intake supports health, while excess can cause harm

Iodine: The Tiny Mineral That Powers Your Metabolism

Iodine is essential for the production of thyroid hormones, which regulate basal metabolic rate, growth, and development. These hormones influence how fast your body uses energy, maintains body temperature, and supports normal physical and brain development.^[6]

Iodine and Thyroid Hormones

Without sufficient iodine, the thyroid gland cannot produce adequate thyroid hormone, leading to hypothyroidism. Common symptoms include fatigue, sensitivity to cold, constipation, weight gain, depression, dry skin, and paleness. Over time, the thyroid may enlarge in an effort to capture more iodine from the bloodstream, resulting in a visible swelling in the neck called a goiter.

Iodine Deficiency Across the Life Span

While goiter is the most noticeable sign of long-term iodine deficiency, the most serious consequences occur during pregnancy, infancy, and childhood. Thyroid hormones play a critical role in brain development, and severe iodine deficiency during early life can lead to cretinism, a condition marked by profound physical and intellectual impairment.

Globally, iodine deficiency remains a major public health issue. The World Health Organization estimates that more than two billion people are affected worldwide, making iodine deficiency the leading cause of preventable brain damage.

How Much Iodine Do You Need?

The adult Recommended Dietary Allowance (RDA) for iodine is 150 micrograms per day, with higher needs during pregnancy and lactation. To prevent excessive intake, a Tolerable Upper Intake Level (UL) of 1,100 micrograms per day has been established for adults.

Where Iodine Comes From

Iodine content of foods depends heavily on geography, since iodine is most abundant in seawater. Foods from coastal regions tend to contain more iodine than those grown inland.

Major dietary sources include:

• Iodized salt

• Seafood (such as cod and tuna)

• Dairy products (milk and yogurt)

• Eggs

• Seaweed (very high and variable—can easily exceed needs)

Key takeaway: Iodine is required in tiny amounts, but its impact on metabolism and brain development is enormous. Thanks to iodized salt, iodine deficiency is uncommon in the U.S.—but globally, it remains a critical nutrition challenge.

Chromium: The Insulin Helper with an Unclear Role

Chromium is a trace mineral whose functions in the body are still not fully understood, making it one of the more mysterious nutrients in nutrition science. What is known is that chromium enhances insulin’s action, the hormone responsible for moving glucose from the bloodstream into cells. Through this role, chromium is involved in the metabolism of carbohydrates, fats, and proteins.

Because of its connection to insulin, chromium has attracted attention for its potential role in blood glucose control and type 2 diabetes. However, research on chromium supplementation has produced mixed and inconclusive results. Some studies suggest modest benefits, while others show little to no effect. At this time, there is no strong evidence to support routine chromium supplementation for diabetes prevention or treatment, and more research is needed to clarify whether chromium is beneficial—and at what dose.

Chromium is naturally present in a variety of foods, including whole grains, nuts, and yeast, and most people can meet their needs through a balanced diet. The recommended daily intake is 35 micrograms per day for adult males and 25 micrograms per day for adult females. Because chromium toxicity has not been clearly demonstrated, there is currently no established Tolerable Upper Intake Level (UL).^[7]

Key takeaway: Chromium plays a role in insulin action and metabolism, but its overall impact on health remains uncertain, highlighting

Fluoride: Tooth Protector with Ongoing Debate

Fluoride is best known for its role in preventing tooth decay. It strengthens teeth and helps maintain bone mineral structure, but unlike minerals such as iron or iodine, fluoride is not currently classified as an essential nutrient. This means it is not required for basic survival or growth, even though it provides clear health benefits for dental health.^[8]

Fluoride helps prevent cavities in three main ways:

• Reduces acid production by oral bacteria

• Slows the demineralization of tooth enamel

• Enhances remineralization of damaged enamel

Fluoride in the Water Supply

Fluoride was first added to public drinking water in 1945 in Grand Rapids, Michigan. Today, more than 60% of the U.S. population receives fluoridated water. Public health data show that water fluoridation reduces cavities by about 25–30% in children and 20–40% in adults, leading many health organizations to consider it a major public health success.^[9]

At the same time, community water fluoridation remains controversial. Supporters emphasize its effectiveness, safety, and role in reducing dental health disparities. Critics raise concerns about long-term exposure, individual choice, and potential overconsumption. ^[10] These debates continue, especially as alternative sources of fluoride (toothpaste, mouth rinses, supplements) have become widely available.

Fluoride Safety and Fluorosis

Fluoride intake must be kept within a healthy range. Excess fluoride exposure during early childhood—before permanent teeth erupt—can cause dental fluorosis, a condition marked by mottling or discoloration of tooth enamel. For this reason, the concentration of fluoride in drinking water is carefully regulated.

Fluoride and Infants & Young Children

Special caution is recommended for babies and young children:

• Infants do not need fluoride supplements unless prescribed

• Fluoridated toothpaste should be avoided in infants

• Young children should use only a rice-sized amount of toothpaste once brushing begins and should not swallow it.

These precautions help reduce the risk of fluorosis while still allowing fluoride to protect developing teeth.

Diet and Fluoride Intake

Most fluoride intake comes from fluoridated drinking water. Other sources include tea, grape juice, and foods prepared with fluoridated water. Solid foods generally contain small amounts unless grown or processed in fluoride-rich environments.

Fluoride and Bone Health

Fluoride’s role in bone health is less clear. Although it can stimulate bone-forming cells and increase bone mineral density, it has not been approved as a treatment for osteoporosis because studies show inconsistent benefits and potential side effects at high doses—levels much higher than those found in drinking water.

Overall, fluoride is highly effective for preventing tooth decay, but it is not considered an essential nutrient, and its use in water and dental products requires careful balance, especially for infants and young children.

Toxic Trace minerals: Lead, Mercury, and Arsenic

Not all trace minerals are beneficial. Lead, mercury, and arsenic are sometimes grouped with trace minerals because they are present in very small amounts in the environment, but they serve no useful biological function in the human body. Instead, these elements are toxic, and even low-level, long-term exposure can cause serious health problems.^[11]

Lead: A Neurotoxin

Lead exposure primarily affects the nervous system, making it especially dangerous for infants and young children. Lead can impair brain development, lower IQ, disrupt behavior, and interfere with learning. In adults, lead exposure is associated with hypertension, kidney damage, and reproductive problems. Because lead accumulates in bone and soft tissues, its effects may persist long after exposure ends.

Mercury: Damage to the Brain and Nervous System

Mercury is another potent neurotoxin. The most common dietary exposure occurs through methylmercury found in certain fish. High or chronic exposure can impair motor function, memory, and coordination, and fetal exposure during pregnancy can lead to long-lasting neurological damage. ^[12] For this reason, pregnant individuals are advised to limit intake of high-mercury fish.

Arsenic: A Widespread Environmental Contaminant

Arsenic occurs naturally in soil and water but is also released through industrial processes, including mining. Chronic arsenic exposure has been linked to skin lesions, cardiovascular disease, impaired immune function, and increased cancer risk. Drinking water contaminated with arsenic is a major concern in some regions.^[13]

Environmental Exposure and Coal Mining Communities

Exposure to toxic trace elements is often tied to environmental pollution, particularly in communities located near mining and industrial sites. Coal mining regions have historically faced elevated exposure to heavy metals due to contaminated soil, air, and water.

A well-known example is McDowell County, West Virginia, where decades of coal mining have contributed to environmental contamination.^[14] Pollutants released from mining operations and coal processing have been associated with increased rates of respiratory disease, cardiovascular illness, and developmental concerns, highlighting how environmental exposure to toxic elements can compound existing health and socioeconomic challenges.

Attributions

This section is an adaptation of:

• “Vitamins and Minerals Involved in Blood Health” in Nutrition: Science and Everyday Application, v. 1.0 by Alice Callahan, PhD; Heather Leonard, MEd, RDN; and Tamberly Powell, MS, RDN licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
• “Iodine” 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.
• “Fluoride” 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.