Zinc, Selenium, and Iodine: The Trace Minerals Worth Understanding

What Makes a Mineral a 'Trace' Mineral?

Not all minerals are needed in equal amounts. While calcium and magnesium are sometimes called macromininerals because the body requires them in relatively larger quantities, trace minerals — also called microminerals — are only needed in milligrams or micrograms per day. That small requirement doesn't reflect small importance. Zinc, selenium, and iodine each support processes the body cannot manage without them.

For a broader overview of how these fit into the full micronutrient picture, see The Everyday Eater's Reference to Essential Micronutrients.

Zinc: Far More Than an Immune Booster

Zinc is involved in over 300 enzymatic reactions — meaning it acts as a helper molecule for enzymes that carry out functions ranging from DNA synthesis to protein production to wound healing. It also plays a documented role in immune cell development and sensory function, including taste and smell.

Key food sources: Oysters are the single richest source of zinc in the food supply. Red meat, poultry, beans, nuts, whole grains, and fortified breakfast cereals also contribute meaningfully. Plant-based eaters should be aware that compounds called phytates in legumes and grains can reduce zinc's bioavailability, so variety and adequate overall intake matter more for this group.

Selenium: A Trace Mineral With Antioxidant Duties

Selenium is incorporated into a family of proteins called selenoproteins, which perform antioxidant and anti-inflammatory functions inside cells. One well-known example is glutathione peroxidase, an enzyme that helps protect cells from oxidative damage. Selenium also supports thyroid hormone metabolism.

Key food sources: Brazil nuts are remarkably concentrated — even one or two per day can meet the daily RDA. Seafood, organ meats, muscle meats, eggs, and grains grown in selenium-rich soil are also reliable sources. Soil selenium content varies significantly by region, which affects the selenium content of plant foods.

Needs can shift across life stages — the guide to micronutrients across a lifetime covers how selenium and other requirements evolve from childhood onward.

Iodine: Essential for Thyroid Function

Iodine's primary role is structural: it is literally built into thyroid hormones (thyroxine and triiodothyronine), which regulate metabolism, energy production, and normal development. Adequate iodine intake is particularly critical during pregnancy and early childhood, when thyroid hormones guide brain and nervous system development. Individuals who are pregnant or breastfeeding have higher iodine needs and should consult a healthcare provider about appropriate intake.

Key food sources: In the United States, iodized salt has been a major source of iodine since the 1920s, effectively reducing deficiency. Dairy products, seafood, and eggs also supply meaningful amounts. Many specialty or artisanal salts are not iodized, so relying exclusively on them without compensating through other sources could reduce iodine intake over time.

If you want to assess how your overall eating pattern stacks up on micronutrients, the micronutrient gap self-assessment offers a practical checklist approach.

This article is for general informational and educational purposes only and does not constitute medical or dietary advice. For questions about your individual nutritional needs, consult a qualified healthcare professional or registered dietitian.