Trace Minerals

1. What are Trace Minerals?

Trace minerals are classified as minerals required in the diet daily in smaller amounts, specifically 100 milligrams or less. These include copper, zinc, selenium, iodine, chromium, fluoride, manganese, molybdenum, and others. Although trace minerals are needed in smaller amounts, it is important to remember that a deficiency in a trace mineral can be just as detrimental to your health as a major mineral deficiency.

term to know

Trace Minerals

Minerals required in the diet each day in smaller amounts, specifically 100 milligrams or less.

2. Iron

Red blood cells contain the oxygen-carrier protein hemoglobin. It is composed of four globular peptides, each containing a heme complex. In the center of each heme lies iron. Iron is needed for the production of other iron-containing proteins such as myoglobin. Myoglobin is a protein found in the muscle tissues that enhances the amount of available oxygen for muscle contraction. Iron is also a key component of hundreds of metabolic enzymes. Many of the proteins in the electron-transport chain contain iron–sulfur clusters involved in the transfer of high-energy electrons and ultimately ATP synthesis.

Iron is also involved in numerous metabolic reactions that take place mainly in the liver and detoxify harmful substances. Moreover, iron is required for DNA synthesis. The great majority of iron used in the body is recycled from the continuous breakdown of red blood cells.

key concept

Hemoglobin is composed of four peptides. Each contains a heme group with iron in the center. The iron in hemoglobin binds to oxygen in the capillaries of the lungs and transports it to cells, where the oxygen is released. If iron level is low, hemoglobin is not synthesized in sufficient amounts, and the oxygen-carrying capacity of red blood cells is reduced, resulting in anemia. When iron levels are low in the diet, the small intestine more efficiently absorbs iron in an attempt to compensate for the low dietary intake, but this process cannot make up for the excessive loss of iron that occurs with chronic blood loss or low intake.

When blood cells are decommissioned for use, the body recycles the iron back to the bone marrow, where red blood cells are made. The body stores some iron in the bone marrow, liver, spleen, and skeletal muscle. A relatively small amount of iron is excreted when cells lining the small intestine and skin cells die, and in blood loss, such as during menstrual bleeding. The lost iron must be replaced from dietary sources.

The bioavailability of iron is highly dependent on dietary sources. In animal-based foods, about 60 percent of iron is bound to hemoglobin, and heme iron is more bioavailable than nonheme iron. The other 40 percent of iron in animal-based foods is nonheme, which is the only iron source in plant-based foods. Some plants contain chemicals (such as phytate, oxalates, tannins, and polyphenols) that inhibit iron absorption. However, eating fruits and vegetables rich in vitamin C at the same time as iron-containing foods markedly increases iron absorption. Vegans are at higher risk for iron deficiency, but careful meal planning can prevent its development. Iron deficiency is the most common of all micronutrient deficiencies.

terms to know

Hemoglobin

An Oxygen-carrier protein in Red blood cells.

Iron

A trace mineral that is needed for the production of other iron-containing proteins such as myoglobin.

Myoglobin

A protein found in the muscle tissues that enhances the amount of available oxygen for muscle contraction.

2a. Iron Toxicity

The body excretes little iron, and therefore, the potential for accumulation in tissues and organs is considerable. Iron accumulation in certain tissues and organs can cause a host of health problems in children and adults, including extreme fatigue, arthritis, joint pain, and severe liver and heart toxicity. In children, death has occurred from ingesting as little as 200 mg of iron, and therefore, it is critical to keep iron supplements out of children’s reach.

The Institute of Medicine has set tolerable upper intake levels of iron. Mostly a hereditary disease, hemochromatosis is the result of a genetic mutation that leads to abnormal iron metabolism and an accumulation of iron in certain tissues, such as the liver, pancreas, and heart. The signs and symptoms of hemochromatosis are similar to those of iron overload in tissues caused by high dietary intake of iron or other non-genetic metabolic abnormalities, but are often increased in severity.

2b. Dietary Reference Intakes and Sources of Iron

The following charts indicate the dietary reference intakes and sources of iron.

2c. Iron-Deficiency Anemia

Iron-deficiency anemia is a condition that develops from having insufficient iron levels in the body, resulting in fewer and smaller red blood cells containing lower amounts of hemoglobin. Regardless of the cause (be it from low dietary intake of iron or via excessive blood loss), iron-deficiency anemia has the following signs and symptoms, which are linked to the essential functions of iron in energy metabolism and blood health:

• Fatigue
• Weakness
• Pale skin
• Shortness of breath
• Dizziness
• Swollen, sore tongue
• Abnormal heart rate

key concept

Iron-deficiency anemia is diagnosed from characteristic signs and symptoms and confirmed with simple blood tests that count red blood cells and determine hemoglobin and iron content in blood. Anemia is most often treated with iron supplements and increases the consumption of foods that are higher in iron. Iron supplements have some adverse side effects, including nausea, constipation, diarrhea, vomiting, and abdominal pain. Reducing the dose at first and then gradually increasing to the full dose often minimizes the side effects of iron supplements.

Avoiding foods and beverages high in phytates, and also tea (which contains tannic acid and polyphenols, both of which impair iron absorption), is important for people who have iron-deficiency anemia. Eating a dietary source of vitamin C at the same time as iron-containing foods improves absorption of nonheme iron in the gut. Additionally, unknown compounds that likely reside in muscle tissue of meat, poultry, and fish increase iron absorption from both heme and nonheme sources.

term to know

Anemia

A condition that develops from having insufficient iron levels in the body resulting in fewer and smaller red blood cells containing lower amounts of hemoglobin.

2d. Iron Deficiency: A Worldwide Nutritional Health Problem

The Centers for Disease Control and Prevention reports that iron deficiency is the most common nutritional deficiency worldwide. The WHO estimates that 80 percent of people are iron deficient, and 30 percent of the world population has iron-deficiency anemia. The main causes of iron deficiency worldwide are parasitic worm infections in the gut, causing excessive blood loss, and malaria, a parasitic disease causing the destruction of red blood cells. In the developed world, iron deficiency is more the result of dietary insufficiency and/or excessive blood loss occurring during menstruation or childbirth.

IN CONTEXT

At-risk populations, including infants, children, adolescents, and women, are the populations most at risk worldwide for iron-deficiency anemia by all causes. Infants, children, and even teens require more iron because iron is essential for growth. In these populations, iron deficiency (and eventually iron-deficiency anemia) can also cause the following signs and symptoms: poor growth, failure to thrive, and poor performance in school, as well as mental, motor, and behavioral disorders. Women who experience heavy menstrual bleeding or who are pregnant require more iron in the diet. One more high-risk group is the elderly. Both elderly men and women have a high incidence of anemia, and the most common causes are dietary iron deficiency and chronic disease, such as ulcers, inflammatory diseases, and cancer. Additionally, those who have recently suffered from traumatic blood loss—frequently donate blood, or take excessive antacids for heartburn—need more iron in the diet.

2e. Preventing Anemia

In young children, iron-deficiency anemia can cause significant motor, mental, and behavioral abnormalities that are long-lasting.

did you know

In the United States, the high incidence of iron-deficiency anemia in infants and children was a major public-health problem prior to the early 1970s, but now the incidence has been greatly reduced. This achievement was accomplished by implementing the screening of infants for iron-deficiency anemia in the health sector as a common practice, advocating the fortification of infant formulas and cereals with iron, and distributing them in supplemental food programs, such as that within Women, Infants, and Children (WIC). Breastfeeding, iron supplementation, and delaying the introduction of cow’s milk for at least the first twelve months of life were also encouraged. These practices were implemented across the socioeconomic spectrum, and by the 1980s, iron-deficiency anemia in infants had significantly declined. Other solutions had to be introduced in young children, who no longer were fed breast milk or fortified formulas and were consuming cow’s milk. The following solutions were introduced to parents: provide a diet rich in sources of iron and vitamin C, limit cow’s milk consumption to less than twenty-four ounces per day, and a multivitamin containing iron.

3. Copper

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 copper deficiency can cause anemia from the lack of iron mobilization in the body for red blood cell synthesis. Other signs and symptoms include delayed growth in children and neurological problems because copper is a cofactor for an enzyme that synthesizes myelin, which surrounds many nerves.

term to know

Copper

An antioxidant that assists in electron transfer in the electron-transport chain. It is a cofactor of enzymes essential for iron absorption and transport.

4. Zinc

Zinc is a cofactor for more than 200 enzymes in the human body and plays a direct role in RNA, DNA, and protein synthesis. Zinc is also a cofactor for enzymes involved in energy metabolism. As a result of its prominent roles in anabolic and energy metabolism, a zinc deficiency in infants and children blunts growth. The reliance of growth on adequate dietary zinc was discovered in the early 1960s in the Middle East, where adolescent nutritional dwarfism was linked to diets containing high amounts of phytate.

key concept

Cereal grains and some vegetables contain chemicals, one being phytate, which blocks the absorption of zinc and other minerals in the gut. It is estimated that half of the world’s population has a zinc-deficient diet.

This is largely a consequence of the lack of red meat and seafood in the diet and reliance on cereal grains as the main dietary staple. In adults, severe zinc deficiency can cause hair loss, diarrhea, skin sores, loss of appetite, and weight loss. Zinc is a required cofactor for an enzyme that synthesizes the heme portion of hemoglobin, and severely deficient zinc diets can result in anemia.

term to know

Zinc

A cofactor for over two hundred enzymes in the human body and plays a direct role in RNA, DNA, and protein synthesis.

4a. Dietary Reference Intakes and Sources of Zinc

The following charts indicate the dietary reference intakes and dietary sources for zinc.

5. Iodine

Iodine is essential for the synthesis of thyroid hormone, which regulates basal metabolism, growth, and development. Low iodine levels, and the resulting hypothyroidism, have many signs and symptoms, including fatigue, sensitivity to cold, constipation, weight gain, depression, dry, itchy skin, and paleness.

key concept

The development of goiter may often be the most visible sign of chronic iodine deficiency, but the consequences of low levels of thyroid hormone can be severe during infancy, childhood, and adolescence, as it affects all stages of growth and development. Thyroid hormone plays a major role in brain development and growth, and fetuses and infants with severe iodine deficiency develop a condition known as cretinism, in which physical and neurological impairment can be severe. The World Health Organization (WHO) estimates iodine deficiency affects over two billion people worldwide, and it is the number-one cause of preventable brain damage worldwide.

term to know

Iodine

A trace mineral that is essential for the synthesis of thyroid hormone, which regulates basal metabolism, growth, and development.

5a. Dietary Reference Intakes and Sources of Iodine

The following charts indicate the dietary reference intakes and dietary sources for iodine.

The mineral content of foods is greatly affected by the soil from which it grew, and thus geographic location is the primary determinant of the mineral content of foods. For instance, iodine comes mostly from seawater, so the greater the distance from the sea, the lesser the iodine content in the soil.

REFERENCES

Fact Sheet for Health Professionals: Zinc. National Institute of Health, Office of Dietary Supplements. ods.od.nih.gov/factsheets/Zinc-HealthProfessional/. Updated February 11, 2016. Accessed November 10, 2017.

Health Professional Fact Sheet: Iodine. National Institute of Health, Office of Dietary Supplements. ods.od.nih.gov/factsheets/Iodine-HealthProfessional/. Updated June 24, 2011. Accessed November 10, 2017.