Small Doses, Large Consequences
Trace minerals are minerals required in amounts under 100mg per day — typically measured in micrograms. They're "trace" by concentration, not by importance. Selenium is essential for thyroid hormone conversion. Iodine is the structural component of thyroid hormones. Zinc is a cofactor in over 300 enzymatic reactions. Boron influences testosterone metabolism and vitamin D function. Chromium plays a role in insulin signaling.
The reason most health-conscious people don't think about trace minerals is that in theory, a diverse whole-food diet should provide all of them. In practice, several factors undermine that assumption: soil depletion, food processing, dietary restriction, and the geographic variation in soil mineral content.
This post covers the most practically relevant trace minerals, who may be deficient, what the research supports for supplementation, and how to tell whether any of this matters for you.
Related: Want to put this into practice? Try our Vitamin D Dosage Calculator to get started, and check out Boron for Testosterone: The Overlooked Mineral for more context.
Selenium
Role: Selenium is a structural component of selenoproteins, including glutathione peroxidases (antioxidant enzymes) and deiodinases (enzymes that convert inactive T4 thyroid hormone to active T3). Selenium also plays a role in immune function and DNA repair.
Deficiency risk: Selenium content in food varies dramatically with soil content. Regions with selenium-poor soil (parts of China, Europe, New Zealand) have higher rates of selenium deficiency. In the US, selenium content in food tends to be more adequate due to selenium-rich Great Plains soil — but this isn't universal.
Signs that may warrant testing: Poor thyroid function markers, low antioxidant capacity, selenium-poor diet (vegan/vegetarian without nut variety or geographic awareness).
Supplementation: The recommended dietary allowance for adults is 55mcg/day. Upper tolerable intake is 400mcg. Two Brazil nuts provide approximately 100–200mcg — enough to meet daily needs, making Brazil nuts one of the most efficient food-based sources.
Caution: Selenium toxicity (selenosis) is possible with supplementation. High-dose selenium supplements (200mcg+) used long-term may have risks that outweigh benefits in selenium-adequate individuals. Test before supplementing high doses.
Iodine
Role: Iodine is required for the synthesis of thyroid hormones T3 and T4. It's one of the few minerals where deficiency has a dramatic, visible consequence (goiter) in severe cases, and more subtle effects on thyroid function at lower levels of deficiency.
Deficiency risk: Iodized salt, widely introduced in the early 20th century, dramatically reduced iodine deficiency in developed countries. However, people who use non-iodized salt (sea salt, Himalayan salt) and don't eat seafood or dairy may have lower iodine intake. Those following whole-food or paleo diets that avoid iodized salt are a relevant population.
Supplementation: Most multivitamins include iodine (typically 150mcg, the RDA). Dedicated iodine supplements are available but unnecessary if dietary intake is adequate. Seafood (especially white fish and shellfish) and dairy are the most reliable food sources.
Caution: Excess iodine can worsen thyroid conditions (particularly Hashimoto's thyroiditis). People with known thyroid conditions should check with their physician before supplementing iodine beyond standard dietary amounts.
If you cook with Himalayan pink salt, sea salt, or kosher salt instead of iodized table salt, and don't eat seafood regularly, iodine is worth considering. These alternative salts are not iodized — they're mineral-rich, but iodine is not one of those minerals.
Zinc
Role: Zinc is a cofactor in over 300 enzymes, involved in immune function, protein synthesis, wound healing, DNA synthesis, and testosterone metabolism. It's well-known in the supplement world for immune support and testosterone optimization.
Deficiency risk: Zinc absorption is reduced by phytic acid in grains and legumes — making vegans and vegetarians more susceptible. Heavy sweating also increases zinc loss, making athletes more prone to marginal deficiency. Alcohol interferes with zinc absorption and increases excretion.
Supplementation: 8–11mg/day is the RDA. Most people who eat meat regularly get adequate zinc from food. Those who sweat heavily, eat plant-based diets, or drink alcohol regularly may benefit from supplementation.
Dose: 15–30mg elemental zinc per day is a common supplement dose. Zinc bisglycinate or zinc picolinate are the better-absorbed forms versus zinc oxide. Take with food to reduce GI irritation.
Important: Zinc competes with copper for absorption. Long-term zinc supplementation without copper (2mg copper for every 15mg zinc) can cause copper deficiency. This is often overlooked.
Boron
Role: Boron is a trace mineral that has received growing research attention for its effects on testosterone and estrogen metabolism, bone density, vitamin D bioavailability, and inflammation markers. It influences the enzymes that regulate steroid hormone metabolism.
Research signals: Several small studies suggest boron supplementation (6–12mg/day) may modestly increase free testosterone, reduce sex hormone binding globulin (SHBG), and improve vitamin D and magnesium bioavailability. The evidence is preliminary but consistent enough to generate interest in optimization communities.
Deficiency risk: Western diets are often low in boron due to low fruit, vegetable, nut, and legume intake — the primary boron food sources. Estimated average intake is 1–3mg/day; some researchers suggest 3–6mg/day as a more functional target.
Supplementation: 3–6mg daily is a reasonable starting dose. Boron citrate or glycinate are common forms. Risk of toxicity at these doses is low.
Chromium
Role: Chromium (specifically trivalent chromium) potentiates the action of insulin. It's involved in glucose uptake and macronutrient metabolism.
Research context: Chromium picolinate supplements were heavily marketed in the 1990s for blood sugar control and body composition. The evidence for benefit in people without insulin resistance is weak. In people with type 2 diabetes or prediabetes, some studies suggest a modest effect on blood glucose markers.
Supplementation: For healthy people without insulin dysregulation, the case for chromium supplementation is weak. If you're tracking fasting glucose and HbA1c and seeing values that concern you, discuss chromium (and the broader insulin regulation picture) with a healthcare provider.
Pros
- +Selenium, iodine, and zinc deficiency are common in specific dietary patterns and verifiable with testing
- +Boron has emerging evidence for modest effects on free testosterone and vitamin D bioavailability
- +Trace mineral deficiencies often produce subtle symptoms that resolve with correction
- +Food sources exist for most trace minerals — diet optimization is often sufficient before supplementation
Cons
- -Selenium toxicity is a real risk with high-dose supplementation — testing before supplementing is important
- -Iodine supplementation can worsen autoimmune thyroid conditions
- -Zinc long-term requires copper co-supplementation to prevent deficiency
- -The evidence base for most trace mineral supplements is weaker than for macronutrients
Do You Actually Need a Trace Mineral Supplement?
The honest answer: most people with varied whole-food diets do not need a dedicated trace mineral supplement. The case for supplementation is stronger if you:
- Eat a primarily plant-based diet (zinc and selenium may be lower)
- Use non-iodized specialty salts and don't eat seafood (iodine)
- Are a heavy sweater or serious athlete (zinc)
- Eat a Western diet low in fruits, vegetables, and nuts (boron, selenium)
- Live in a region with selenium-depleted soils
Before buying a trace mineral product, consider testing. A comprehensive micronutrient panel (available through specialty labs) or at minimum a basic metabolic panel plus zinc, selenium, and vitamin D can tell you where you actually stand.
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The Bottom Line
Trace minerals are small in concentration and large in consequence. Deficiencies in selenium, iodine, and zinc are real risks in specific dietary patterns. Boron is an underappreciated mineral with emerging evidence for hormone and vitamin D interactions. The best approach is to test, identify your actual gaps, and target supplementation precisely rather than taking a broad-spectrum trace mineral product and assuming you've covered all the bases.