3 Micronutrients

Micronutrient roles and safe intake

Micronutrients are vitamins and minerals required in small amounts. They do not provide energy, but they help the body release energy from food, build and maintain tissues, support immunity, and regulate processes such as nerve signaling and fluid balance.

Adequate intake supports normal function, but more is not necessarily better. Excessive intake, especially from supplements or highly fortified products, can be harmful. A varied diet can provide many micronutrients; fortified foods or supplements may be useful in particular circumstances, but an essential nutrient is not automatically safe at high doses.

Vitamin types, roles, and sources

Vitamins are organic compounds. The body makes too little or none of most vitamins, so they must come from food or other sources. Fat-soluble vitamins are absorbed with dietary fat and can be stored in the body; water-soluble vitamins generally circulate in water and are excreted more readily. Water-soluble vitamins can still cause harm at high doses.

Fat-soluble vitamins

• Vitamin A supports vision, immune function, growth, and tissue maintenance. Sources include liver, eggs, and dairy; orange and dark-green vegetables provide carotenoids that the body can convert to vitamin A.

• Vitamin D helps the body absorb calcium and supports bones and muscles. Sources include fatty fish and fortified foods; the skin also makes vitamin D after sun exposure.

• Vitamin E protects cell membranes from oxidative damage. Sources include vegetable oils, nuts, and seeds.

• Vitamin K is needed for blood clotting and contributes to bone-related processes. Sources include leafy green vegetables and some vegetable oils.

Water-soluble vitamins

• Vitamin C supports collagen formation and antioxidant defenses, and improves absorption of iron from plant foods. Sources include citrus fruit, berries, peppers, tomatoes, and broccoli.

• B1 (thiamin) helps enzymes release energy from nutrients and supports nerve function. Sources include pork, legumes, and whole or enriched grains.

• B2 (riboflavin) helps energy metabolism and supports normal cell function. Sources include dairy, eggs, meats, and enriched grains.

• B3 (niacin) supports energy metabolism and cellular reactions. Sources include meat, fish, peanuts, and enriched grains; the body can also make some niacin from tryptophan.

• B5 (pantothenic acid) and B7 (biotin) help form coenzyme A and support metabolism. They occur in a wide variety of foods, including meats, legumes, eggs, and whole grains.

• B6 (pyridoxine) supports amino-acid metabolism, neurotransmitter production, and hemoglobin formation. Sources include poultry, fish, potatoes, bananas, and legumes.

• B9 (folate) is needed for DNA synthesis and cell division and is especially important during early pregnancy. Sources include leafy greens, legumes, citrus, and fortified grains.

• B12 (cobalamin) supports red-blood-cell formation and normal nerve function. Natural sources are primarily animal foods; some plant-based foods are fortified.

Vitamin inadequacy and excess

Both inadequate and excessive vitamin intake can cause harm. The effects listed here are examples, not a diagnostic checklist; symptoms can be nonspecific and may have causes other than diet.

• Vitamin A: Deficiency can impair vision, including causing night blindness. Excess preformed vitamin A can damage the liver and cause birth defects. High carotenoid intake can harmlessly tint the skin yellow-orange.

• Vitamin D: Deficiency can cause rickets in children and osteomalacia in adults. Excess, usually from supplements, can raise blood calcium and damage the kidneys.

• Vitamin E: Deficiency is uncommon but can cause nerve or muscle problems and red-blood-cell damage. High supplemental doses can increase bleeding risk.

• Vitamin K: Deficiency can cause abnormal bleeding. Vitamin K from foods is not generally associated with toxicity, but changes in intake can affect warfarin treatment.

• Vitamin C: Deficiency causes scurvy, which can include fatigue, gum problems, and poor wound healing. Very high supplemental intake can cause gastrointestinal symptoms and may raise kidney-stone risk in susceptible people.

• B1 (thiamin): Deficiency can cause beriberi or, in severe cases, Wernicke–Korsakoff syndrome. Toxicity from food is rare.

• B2 (riboflavin): Deficiency can cause mouth and skin changes. Toxicity is uncommon.

• B3 (niacin): Severe deficiency causes pellagra, classically involving dermatitis, diarrhea, and cognitive changes. High-dose supplements can cause flushing and, at sufficiently high doses, liver injury.

• B5 (pantothenic acid) and B7 (biotin): Deficiencies are rare. Biotin deficiency can cause skin changes and hair loss; high biotin supplements can interfere with some laboratory tests.

• B6 (pyridoxine): Deficiency can cause anemia, skin changes, or neurologic symptoms. Chronic high supplemental doses can damage peripheral nerves.

• B9 (folate): Deficiency can cause megaloblastic anemia. Inadequate folate around conception raises the risk of neural-tube defects; large amounts of folic acid can mask signs of vitamin B12 deficiency.

• B12 (cobalamin): Deficiency can cause megaloblastic anemia and potentially lasting nerve damage. It is more likely with impaired absorption or a diet lacking reliable B12 sources. No UL has been established for healthy people.

Mineral roles, sources, and risks

Minerals are inorganic elements. Major minerals are needed in comparatively large amounts, while trace minerals are needed in smaller amounts; the amount needed does not indicate importance, because both groups are essential. Minerals may be part of body structures, such as bone, or help regulate fluid balance, muscle contraction, oxygen transport, and enzyme activity.

Major minerals

• Calcium builds bones and teeth and supports muscle contraction and nerve signaling. Sources include dairy, calcium-set tofu, and some leafy greens or fortified foods. Low intake over time can compromise bone health. Excess, particularly from supplements, can contribute to kidney stones and interfere with absorption of other minerals.

• Phosphorus is part of bones, cell membranes, and energy-carrying molecules. Sources include dairy, meat, fish, beans, nuts, and many processed foods. Deficiency is uncommon with usual diets. Excess can disrupt mineral balance, especially when kidney function is impaired.

• Magnesium supports hundreds of enzyme reactions, muscle and nerve function, and bone structure. Sources include nuts, seeds, legumes, whole grains, and leafy greens. Deficiency can cause weakness or cramps and, in severe cases, abnormal heart rhythms. Excess from supplements or medicines can cause diarrhea; very high levels can be dangerous, especially with kidney disease.

• Sodium, chloride, and potassium help maintain fluid balance and enable nerve impulses and muscle contraction. Sodium and chloride are common in salt and many packaged foods; potassium is found in potatoes, beans, fruit, vegetables, and dairy. Imbalance can affect blood pressure, nerves, and heart rhythm. Too much sodium can raise blood pressure in many people; excessive potassium can be dangerous with kidney disease or certain medicines.

Trace minerals

• Iron is needed for hemoglobin to carry oxygen and for other metabolic processes. Sources include meat and seafood, beans, lentils, spinach, and iron-fortified grains. Deficiency can cause iron-deficiency anemia; excess can damage organs. Keep iron supplements away from children because accidental overdose can be fatal. Vitamin C can improve absorption of plant-based iron.

• Zinc supports immune function, wound healing, growth, and many enzymes. Sources include meat, shellfish, dairy, beans, nuts, and whole grains. Deficiency can impair growth, immunity, and wound healing. Excess supplements can cause nausea and interfere with copper absorption.

• Iodine is needed to make thyroid hormones, which regulate growth and metabolism. Sources include iodized salt, seafood, dairy, and some seaweeds. Deficiency can enlarge the thyroid and impair thyroid function; severe deficiency during pregnancy can harm fetal development. Excess can also disrupt thyroid function.

• Selenium is part of antioxidant enzymes and supports thyroid function. Sources include seafood, meat, eggs, and grains; amounts in some plant foods vary with soil. Deficiency is uncommon in most varied diets. Chronic excess can cause hair and nail changes, a garlic-like breath odor, and other symptoms.

• Copper helps enzymes, iron use, connective tissue formation, and nervous-system function. Sources include shellfish, nuts, seeds, and organ meats. Deficiency is uncommon but can cause anemia or neurologic problems. Excess can harm the liver, particularly in certain inherited disorders.

• Manganese and molybdenum support enzyme activity; fluoride helps strengthen tooth enamel. Sources include whole grains, legumes, nuts, drinking water, and tea, depending on the mineral. Deficiency is rare. Excess fluoride during tooth development can cause dental fluorosis, and excessive exposure to other trace minerals can also be harmful.

Interpreting nutrient reference values

In the United States and Canada, Dietary Reference Intakes (DRIs) are reference values used to plan and assess nutrient intakes for generally healthy people. Values are tailored to age and other life-stage factors; some also differ by sex, pregnancy, and lactation.

• Estimated Average Requirement (EAR): The intake estimated to meet the needs of half of healthy people in a specified group. It is especially useful for assessing groups.

• Recommended Dietary Allowance (RDA): The intake designed to meet the needs of nearly all—about 97–98%—healthy people in a specified group. It is commonly used as an individual planning goal.

• Adequate Intake (AI): A target used when evidence is not sufficient to establish an EAR and RDA. Intake at or above the AI suggests adequacy; intake below it does not by itself establish inadequacy.

• Tolerable Upper Intake Level (UL): The highest usual daily intake unlikely to pose a risk for most people in the specified group. It is a safety boundary, not a recommended target; exceeding it can increase risk.

A nutrient may have an RDA or an AI, rather than both. Recommendations can change with age and life stage. The amount listed on a food label as a Daily Value (DV) is a general labeling reference, not a personalized intake prescription. Use established DRIs rather than assuming that a supplement dose is beneficial because it exceeds the RDA. People with medical conditions or specific deficiency risks may need individualized advice.

Interpreting adequacy and risk

Risk from inadequate or excessive intake depends on usual intake, absorption, health conditions, medicines, and life stage. Deficiency symptoms are often nonspecific and can have causes other than diet, so the listed effects should not be treated as a diagnostic checklist.

Micronutrients support essential processes but do not supply calories. Both too little and too much can cause harm, and supplements are not automatically safe simply because a nutrient is essential. Dietary Reference Intakes distinguish population requirements, individual planning targets, and upper safety limits; apply them to the appropriate age and life stage.