Chapter 9 – Minerals
9.5 The Trace Minerals: Iron, Zinc, Copper, Iodine, Chromium, and Fluoride
Trace minerals are needed in only small amounts, but they play essential roles in growth, metabolism, immune function, oxygen transport, and hormone production. Even mild deficiencies can have significant health consequences. Among the most important trace minerals are iron, zinc, copper, iodine, chromium, selenium, and fluoride, all of which contribute to vital physiological processes and public health. Information in this section is based primarily on the NIH Vitamin and Mineral Fact Sheets.
Although trace minerals are required in milligram or microgram amounts, obtaining adequate amounts depends on factors such as dietary choices, food processing, soil composition, and physiological needs. Pregnant individuals, infants, adolescents, older adults, and those following restrictive diets may be at increased risk of deficiency.
This section examines the functions, dietary sources, deficiency symptoms, toxicity risks, and public health significance of key trace minerals, illustrating how these small nutrients play a major role in health across the lifespan.
Iron: Essential for Healthy blood and Energy
Iron is an essential trace mineral involved in oxygen transport, energy metabolism, immune function, and brain development. Much of iron’s importance stems from its role in delivering oxygen throughout the body.
Iron is a key component of hemoglobin, the protein in red blood cells that carries oxygen from the lungs to body tissues (Figure 9.13). It is also part of myoglobin, a protein in muscle cells that stores oxygen and releases it during physical activity. Because oxygen is required for energy production, adequate iron is essential for normal metabolism and physical performance.
When iron intake or body iron stores are too low, the body cannot produce enough healthy hemoglobin. As a result, red blood cells become smaller and carry less oxygen, leading to iron-deficiency anemia. Because iron is also involved in cellular energy production, low iron levels can reduce both oxygen delivery and energy metabolism.
Common symptoms of iron deficiency include fatigue, weakness, reduced endurance, difficulty concentrating, and poor physical performance. These symptoms may appear before anemia becomes severe
Who Is Most at Risk?
Iron deficiency is the most common nutrient deficiency worldwide and the leading cause of anemia. Groups at greatest risk include:
- Infants and young children, especially those born prematurely or with low iron stores
- Adolescents, particularly girls, due to rapid growth and menstrual blood loss
- Women of reproductive age, whose iron needs increase because of menstruation
- Pregnant women, who require additional iron to support fetal growth and expanded blood volume
Meeting iron needs can be challenging. For example, a 3-ounce serving of beef provides only about 3 mg of iron, a modest contribution toward the daily needs of many women.
FOOD SOURCES OF IRON
Iron is found in foods in two forms: heme iron and non-heme iron.
Heme iron is found only in animal foods such as meat, poultry, and fish because it is part of the proteins hemoglobin and myoglobin. It is the most readily absorbed form of iron.
Non-heme iron is found in plant foods such as beans, lentils, nuts, vegetables, and whole or fortified grains, as well as in some animal foods. Although non-heme iron is absorbed less efficiently, its absorption can be increased by eating vitamin C-rich foods.
For example, adding tomatoes or bell peppers to a bean chili or drinking orange juice with an iron-fortified cereal can help your body absorb more iron.
Maximizing Iron Absorption
Not all of the iron you eat is absorbed. On average, the body absorbs more iron from mixed diets containing both animal and plant foods than from vegetarian diets. Iron absorption is influenced by the type of iron consumed, the foods eaten with it, and the body’s iron stores. When iron stores are low, the body becomes more efficient at absorbing iron.
Iron needs vary by sex and life stage. Menstruating women require more iron because of monthly blood loss, with an RDA of 18 mg per day compared with 8 mg per day for adult men. As a result, meeting iron needs can be more challenging for women of reproductive age.
🔍 Tips to Boost Iron Absorption
Not all iron is absorbed equally. You can increase iron absorption by pairing iron-rich foods with the right nutrients.
Ways to Boost Iron Absorption
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Add vitamin C–rich foods
Helps the body absorb non-heme iron
Examples: citrus fruits, strawberries, tomatoes, bell peppers, broccoli -
Include animal proteins
Meat, poultry, and seafood enhance the absorption of non-heme iron eaten at the same meal -
Eat iron-rich foods with meals
Balanced meals improve overall nutrient absorption
Foods That Can Reduce Iron Absorption
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Phytates (found in whole grains and legumes)
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Polyphenols (in tea, coffee, and some plant foods)
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Calcium (from supplements or large amounts of dairy)
💡 Plant-Based Tip: Pair beans, lentils, or iron-fortified cereals with vitamin C-rich foods, such as salsa, tomatoes, or orange juice, to increase iron absorption.
Can You Get Too Much Iron?
Because the body has no efficient way to excrete excess iron, high intakes—especially from supplements—can lead to iron buildup in tissues and organs. Over time, iron overload may damage the liver, heart, and other organs.
Iron toxicity is particularly dangerous in children. Accidental ingestion of iron supplements can cause severe poisoning and has resulted in fatalities. For this reason, iron supplements should always be stored out of reach of children. The Tolerable Upper Intake Level (UL) for iron is 45 mg per day for adults.
Some individuals are also at increased risk of iron overload due to hereditary hemochromatosis, a genetic disorder that causes excessive iron absorption. Without treatment, iron can accumulate in organs such as the liver, pancreas, and heart, leading to serious health complications.
Preventing Iron-Deficiency Anemia
Iron-deficiency anemia can impair growth, learning, physical performance, and overall health. Prevention focuses on consuming iron-rich foods, pairing plant sources of iron with vitamin C-rich foods to enhance absorption, and using fortified foods or supplements when needed.
Although iron-deficiency anemia has declined in the United States due to improved screening and food fortification, it remains the most common nutrient deficiency worldwide. Young children, adolescents, women of reproductive age, and pregnant individuals are among the groups at greatest risk.
Zinc and Copper: Essential Partners for Growth and Health
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 trace mineral that serves as a cofactor for hundreds of enzymes involved in DNA, protein synthesis, and energy metabolism. As a result, zinc is essential for growth, immune function, wound healing, and normal taste perception.
Zinc deficiency is most common during periods of rapid growth, such as infancy, childhood, and adolescence. Inadequate zinc intake can impair growth, delay sexual maturation, and weaken immune function. Severe deficiency may cause hair loss, diarrhea, skin problems, loss of appetite, and weight loss. Because zinc also supports heme synthesis, prolonged deficiency can contribute to anemia.
Good sources of zinc include oysters, red meat, pork, seafood, dairy products, beans, nuts, and whole grains. Zinc from animal foods is generally absorbed more efficiently than zinc from plant foods because compounds called phytates can reduce zinc absorption.
Copper: Iron Metabolism and Antioxidant Defense
Copper works closely with iron and plays important roles in energy metabolism, red blood cell formation, and antioxidant defense. It serves as a cofactor for enzymes involved in iron absorption and transport, helping the body use iron effectively. Without adequate copper, anemia can develop even when iron intake is sufficient.
Copper also helps protect cells from oxidative damage and supports the formation of myelin, the protective covering around nerves. Although copper deficiency is rare, severe deficiency may cause anemia, impaired growth, and neurological problems.
Dietary Sources of Zinc and Copper
Good sources of zinc include oysters, red meat, pork, seafood, dairy products, beans, nuts, and whole grains. Zinc from animal foods is generally absorbed more efficiently than zinc from plant foods because phytates can reduce absorption.
Good sources of copper include organ meats, shellfish, nuts, seeds, whole grains, and legumes.
| Food Group | Best Zinc Sources | Best Copper Sources |
|---|---|---|
| Seafood | Oysters, crab, lobster | Shellfish |
| Meat | Beef, pork | Liver, organ meats |
| Dairy | Milk, yogurt, cheese | Small amounts |
| Legumes | Beans | Beans, lentils |
| Nuts & Seeds | Almonds, cashews | Cashews, sunflower seeds, sesame seeds |
| Whole Grains | Oatmeal, whole wheat | Whole wheat |
Together, zinc and copper demonstrate how trace minerals, though required in small amounts, play essential roles in growth, energy metabolism, blood health, immune function, and nervous system function.
Selenium: Thyroid Function and Antioxidant Protection
Selenium is a trace mineral that plays important roles in thyroid hormone regulation and antioxidant defense. It helps convert inactive thyroid hormone into its active form, so a deficiency can produce symptoms similar to iodine deficiency, including fatigue and slowed metabolism.
Selenium is also a component of several antioxidant enzymes that help protect cells from oxidative damage. Although low selenium status has been linked to certain chronic diseases, research has not shown consistent benefits from selenium supplementation, demonstrating that more is not always better.
Intake, Safety, and Food Sources
The RDA for selenium is 55 micrograms per day for adults, and the UL is 400 micrograms per day. Excess intake from supplements can cause toxicity, leading to brittle hair and nails, digestive upset, fatigue, and a garlic-like breath odor.
Good sources of selenium include seafood, meats, poultry, eggs, dairy products, and Brazil nuts. Because selenium content depends on soil conditions, plant foods vary widely in selenium content. Brazil nuts are especially concentrated sources—just one or two nuts can provide a full day’s requirement.
💡 Fun Fact: One Brazil nut may provide more than 100% of your daily selenium needs.
Iodine: The Tiny Mineral That Powers Your Metabolism
Iodine is essential for the production of thyroid hormones, which regulate metabolism, growth, and development. These hormones influence how the body uses energy, maintains body temperature, and support normal brain development.
Without adequate iodine, the thyroid gland cannot produce enough thyroid hormone, leading to hypothyroidism. Common symptoms include fatigue, weight gain, sensitivity to cold, and dry skin. Over time, the thyroid may enlarge, producing a visible swelling in the neck called a goiter (Figure 9.15).
Chromium: The Insulin Helper with an Unclear Role
Chromium is a trace mineral that helps insulin regulate blood glucose levels. Through its effects on insulin, chromium is involved in the metabolism of carbohydrates, fats, and proteins.
Because of its role in insulin function, chromium has been studied as a possible aid for blood glucose control and type 2 diabetes. However, research has produced mixed results, and there is currently no strong evidence to support routine chromium supplementation.
Chromium is found in a variety of foods, including whole grains, nuts, and yeast. Most people can meet their needs through a balanced diet. The recommended intake is 35 micrograms per day for adult males and 25 micrograms per day for adult females. No Tolerable Upper Intake Level (UL) has been established.
Fluoride: Tooth Protector
Fluoride is best known for helping prevent tooth decay. Although it is not classified as an essential nutrient, fluoride strengthens tooth enamel and reduces the risk of cavities.
Fluoride helps protect teeth by:
- Reducing acid production by oral bacteria
- Slowing the loss of minerals from tooth enamel
- Promoting the remineralization of damaged enamel
Fluoride in Drinking Water
Since the mid-1940s, fluoride has been added to many public water supplies to help prevent tooth decay. Today, fluoridated water remains one of the most widely used public health measures to improve dental health and reduce cavities.
Fluoride Safety
Like many nutrients, fluoride is beneficial in appropriate amounts but can be harmful in excess. Too much fluoride during early childhood can cause dental fluorosis, a condition characterized by discoloration or mottling of tooth enamel (Figure 9.17). For this reason, fluoride levels in drinking water are carefully regulated.
Most fluoride comes from fluoridated drinking water, toothpaste, and other dental products. Although fluoride is highly effective at preventing tooth decay, its use requires balance, as excessive intake during childhood can increase the risk of fluorosis.
Toxic Trace minerals: Lead, Mercury, and Arsenic
Not all trace elements are beneficial. Lead, mercury, and arsenic occur naturally in the environment but serve no useful biological function in the human body. Instead, they are toxic, and long-term exposure can harm health.
| Element | Common Sources | Major Health Effects |
|---|---|---|
| Lead | Old paint, contaminated soil, and water | Impaired brain development, learning problems, kidney damage, and hypertension |
| Mercury | Certain fish and seafood | Nervous system damage, impaired memory and coordination, fetal developmental problems |
| Arsenic | Contaminated groundwater, industrial pollution | Skin lesions, cardiovascular disease, impaired immune function, and increased cancer risk |
Pregnant individuals are often advised to limit high-mercury fish because fetal exposure can affect brain development.
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. [1] 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.[2]
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. 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.
Although trace minerals are required in only small amounts, they are essential for oxygen transport, immune function, metabolism, growth, and thyroid function. At the same time, exposure to toxic trace elements highlights the importance of food safety and environmental health. Together, these nutrients demonstrate that even tiny amounts of minerals can have major effects on human health.
Use the table below to review the functions, sources, and deficiency states of the trace minerals.
| Trace Mineral | Major Function | Good Food Sources | Deficiency |
|---|---|---|---|
| Iron | Carries oxygen in bloods | Red meat, beans, fortified cereals, spinach | Iron-deficiency anemia |
| Zinc | Immune function, wound healing, growth | Meat, seafood, beans, nuts | Poor growth, impaired immunity |
| Copper | Iron metabolism, enzyme function | Nuts, seeds, seafood, whole grains | Anemia (rare) |
| Selenium | Antioxidant; thyroid function | Seafood, meats, Brazil nuts | Muscle weakness, Keshan disease (rare) |
| Iodine | Thyroid hormone production | Iodized salt, dairy, seafood | Goiter, hypothyroidism |
| Fluoride | Strengthens teeth and bones | Fluoridated water, tea, seafood | Increased dental caries |
| Chromium | Helps insulin regulate blood glucose | Whole grains, broccoli, meats | Rare; impaired glucose metabolism |
| Molybdenum | Enzyme cofactor | Legumes, grains, milk | Extremely rare |
Review Questions
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.
- Kern JK, Geier DA, Sykes LK, Haley BE, Geier MR. The relationship between mercury and autism: A comprehensive review and discussion. J Trace Elem Med Biol. 2016;37:8-24. doi:10.1016/j.jtemb.2016.06.002 ↵
- Karagas MR, Gossai A, Pierce B, Ahsan H. Drinking Water Arsenic Contamination, Skin Lesions, and Malignancies: A Systematic Review of the Global Evidence. Curr Environ Health Rep. 2015;2(1):52-68. doi:10.1007/s40572-014-0040-x ↵
Natural compounds in many plant foods that can decrease the absorption of certain minerals, especially zinc and iron. Also known as phytic acid.
A toxic form of mercury that builds up in fish and shellfish. High exposure can damage the brain and nervous system, especially in developing fetuses and young children.
