Trace Minerals: Zinc, Selenium, Manganese, Chromium, and Molybdenum – Functions, Sources, Deficiency, and Toxicity

Trace Minerals in Human Nutrition

Zinc (Zn)

Zinc is an essential trace mineral involved in numerous enzymatic and structural functions in the human body. It plays a critical role in growth, immune function, and gene expression.

• Main Bodily Functions:

  • Acts as an enzymatic cofactor for over 300 enzymes.

  • Provides structural stability to proteins.

  • Helps regulate gene expression, especially in fetal development.

  • May reduce the duration of the common cold.

• Food Sources:

  • Fish, meat, and whole grains (especially oysters).

  • Enriched cereals.

• Things That Limit Absorption:

  • Non-heme iron, fiber, phytates.

• Deficiency (Rare):

  • Delayed growth.

  • Delayed sexual maturation.

  • Reduced appetite.

  • Increased susceptibility to infection.

• Excess/Toxicity (Rare):

  • Nausea/diarrhea.

  • Headaches.

  • Impaired immune function.

  • Interferes with copper absorption.

Example: Oysters are an excellent source of zinc.

Selenium (Se)

Selenium is a trace mineral that functions as a cofactor for antioxidant enzymes and is important for thyroid hormone metabolism.

• Main Bodily Functions:

  • Cofactor for many enzymes, especially those involved in antioxidant defense.

  • Critical for thyroid hormone production.

  • May reduce risk of certain cancers.

• Food Sources:

  • Amount in food depends on soil selenium content.

  • Common sources: seafood, meats, grains, eggs.

• Deficiency (Rare):

  • Impaired thyroid function.

  • Keshan disease (heart disorder).

• Excess/Toxicity (Rare):

  • Hair loss and nail brittleness.

  • Skin rashes.

  • Liver damage.

Example: Selenium levels in foods vary depending on soil content; fertilized crops may be higher in selenium.

Manganese (Mn), Chromium (Cr), and Molybdenum (Mo)

These trace minerals serve as enzyme cofactors and are involved in metabolism and other essential body functions.

Mineral	Function	Foods	Deficiency/Toxicity
Manganese	Enzyme cofactor in metabolism	Mollusks, nuts, whole grains	Toxic at large doses (>11 mg/day)
Chromium	Enhances insulin function	Meat, eggs, whole grains	Impaired glucose uptake if deficient; toxicity not reported in humans
Molybdenum	Enzyme cofactor; important for metabolism of amino acids	Milk & dairy products, beans, grains, nuts	Rare toxicity in humans

Example: Chromium enhances insulin function and is found in meats and whole grains.

Key Terms and Definitions

• Trace Mineral: A mineral required in small amounts (<100 mg/day) for normal physiological functions.

• Enzyme Cofactor: A non-protein chemical compound that is required for the biological activity of an enzyme.

• Gene Expression: The process by which information from a gene is used to synthesize a functional gene product, often a protein.

Formulas and Equations

• Recommended Dietary Allowance (RDA): $\text{RDA}_{\text{Zinc}} = 8-11\,\text{mg}$ (adults) $\text{RDA}_{\text{Selenium}} = 55\,\mu\text{g}$ (adults)

Short Comparison Table: Deficiency vs. Toxicity

Mineral	Deficiency	Toxicity
Zinc	Delayed growth, immune dysfunction	Nausea, headaches, impaired copper absorption
Selenium	Impaired thyroid, Keshan disease	Hair loss, liver damage
Chromium	Impaired glucose uptake	Not reported in humans

Additional info: Soil content can significantly affect selenium levels in plant-based foods, which in turn impacts dietary intake.