Micronutrients: Magnesium, Zinc and Selenium

Micronutrients: Small Amounts, Major Impact

Magnesium, zinc, and selenium are essential minerals and trace elements. The body needs them in relatively small amounts, yet without them numerous metabolic processes cannot function properly. Despite their importance, many people in Europe fail to meet the recommended daily intakes. This is due to changing dietary habits, nutrient-depleted soils, and an increasing consumption of ultra-processed foods.

Magnesium: The Underestimated Mineral

Magnesium is involved in over 300 enzymatic reactions in the body. Magnesium contributes to a normal energy-yielding metabolism, normal muscle function, normal functioning of the nervous system, normal protein synthesis and to the reduction of tiredness and fatigue (authorised health claims, EFSA).

DiNicolantonio et al. (2018) estimate that a substantial share of the Western population does not meet the recommended magnesium intake. Ensuring adequate intake through diet is therefore an important goal.

Bioavailability of Different Magnesium Forms

Not all magnesium supplements are created equal. The form of magnesium determines how well the body can absorb it.

Form	Bioavailability	Characteristics
Magnesium citrate	High	Well tolerated, widely available
Magnesium bisglycinate	High	Gentle on the stomach, supports sleep quality
Magnesium taurate	Medium to high	Valued in sports medicine
Magnesium oxide	Low	Inexpensive, but poorly absorbed
Magnesium carbonate	Low to medium	May cause gastrointestinal discomfort

Organic compounds such as citrate and bisglycinate are generally absorbed better than inorganic forms like oxide. While magnesium oxide contains the highest percentage of elemental magnesium, only a fraction is actually absorbed by the body.

Magnesium-Rich Foods

Good natural sources include pumpkin seeds (approx. 535 mg/100 g), sunflower seeds, almonds, cashews, amaranth, and cacao. Dark leafy greens like spinach also provide notable amounts, as magnesium sits at the centre of the chlorophyll molecule.

Zinc: Immune System, Cell Division, and Hormone Metabolism

Zinc is involved in over 300 enzymes and approximately 1,000 transcription factors. Zinc contributes to the normal function of the immune system, to normal DNA synthesis and cell division, and to the maintenance of normal testosterone levels in the blood (authorised health claims, EFSA). Wessels et al. (2017) summarise the role of zinc in immune metabolism in a review.

The body does not have a large zinc reservoir. Therefore, regular dietary intake is necessary. The recommended daily amount is 7-10 mg for women and 11-16 mg for men (DACH reference values). The higher value applies to diets rich in phytic acid, such as whole-food or vegan diets.

The Problem with Phytic Acid

Phytic acid is found in legumes, whole grains, nuts, and seeds. It binds zinc in the digestive tract and can reduce its absorption by up to 50%. Simple preparation methods can lower the phytic acid content:

• Soaking: Soaking for 12-24 hours reduces phytic acid content by 30-70%.
• Sprouting: Sprouting legumes and grains activates the enzyme phytase, which breaks down phytic acid.
• Fermenting: Sauerkraut, sourdough bread, and other fermented foods have a significantly reduced phytic acid content.

Zinc and Testosterone

Zinc contributes to the maintenance of normal testosterone levels in the blood (authorised health claim, EFSA). Prasad et al. (1996) observed changes in serum testosterone levels in young men depending on zinc status. Additional intake beyond requirements showed no further effect in individuals with adequate supply.

Selenium: Thyroid Function and Antioxidant Defence

Selenium is an essential trace element that the body needs in very small amounts (recommended: 60-70 mcg/day). It is a component of at least 25 selenoproteins, including the glutathione peroxidase family and thioredoxin reductase.

Selenium contributes to normal thyroid function, to the normal function of the immune system and to the protection of cells from oxidative stress (authorised health claims, EFSA). Rayman (2012) gives an overview of the role of selenium in metabolism in a review. The thyroid gland has the highest selenium content per gram of tissue in the entire body.

Brazil Nuts: The Selenium Champion

Brazil nuts are by far the richest natural source of selenium. A single Brazil nut contains an average of 70-90 mcg of selenium. This already covers the entire daily requirement. Thomson et al. (2008) demonstrated that consuming two Brazil nuts per day improved selenium status as effectively as a supplement containing 100 mcg of selenomethionine.

Other good selenium sources include fish, seafood, eggs, sunflower seeds, and whole grain products. The selenium content of plant-based foods depends heavily on the selenium content of the soil. European soils tend to be lower in selenium than those in North America.

Interactions Between Minerals

Minerals and trace elements influence each other during absorption. Anyone who supplements should be aware of these interactions.

Zinc-copper antagonism: High zinc doses (over 50 mg/day over extended periods) can inhibit copper absorption. Copper, in turn, is involved in iron metabolism. Long-term supplementation with high zinc doses without copper compensation can therefore lead to secondary copper deficiency. Willis et al. (2005) documented this relationship in patients with long-term high-dose zinc supplementation.

Magnesium and calcium: Both minerals compete for the same transport mechanisms in the gut. Simultaneous intake of very high doses can reduce the absorption of both. At normal dietary levels, this effect is generally negligible.

Selenium and vitamin E: Both nutrients work synergistically in the antioxidant defence system. Selenium as a component of glutathione peroxidase and vitamin E as a fat-soluble antioxidant complement each other.

Comparative Overview

	Magnesium	Zinc	Selenium
Daily requirement	300-400 mg	7-16 mg	60-70 mcg
Best sources	Pumpkin seeds, cacao, almonds	Oysters, beef, pumpkin seeds	Brazil nuts, fish, eggs
Top plant source	Pumpkin seeds (535 mg/100 g)	Pumpkin seeds (7 mg/100 g)	Brazil nuts (~70-90 mcg/nut)
Role in the body	Energy metabolism, muscle and nerve function	Immune system, DNA synthesis, testosterone level	Thyroid function, immune system, cellular protection
Groups at risk of low intake	Athletes, elderly, stressed individuals	Vegans, pregnant women, seniors	People in selenium-poor regions
Best supplement form	Citrate, bisglycinate	Citrate, picolinate, bisglycinate	Selenomethionine, sodium selenite

When Is Supplementation Worthwhile?

The priority should always be a varied, nutrient-rich diet. In certain situations, however, targeted supplementation can be beneficial:

• Check supply status: A blood test from a healthcare provider clarifies the situation. Serum magnesium alone is not very informative, as only around 1% of total body magnesium circulates in the blood.
• Increased demand: Intense exercise, pregnancy or breastfeeding can increase requirements.
• Impaired absorption: Certain medications or high alcohol consumption can affect nutrient absorption. Medical advice is recommended.
• Vegan diet: Zinc intake in particular should be consciously planned with a purely plant-based diet. Prepare phytic acid-rich foods through soaking or sprouting.

Conclusion

Magnesium, zinc, and selenium are indispensable for a wide range of bodily functions. A conscious food selection can ensure adequate supply in most cases. Pumpkin seeds, Brazil nuts, cacao, and dark leafy greens are particularly valuable sources. Those who supplement should choose highly bioavailable forms and consider interactions between minerals. A blood panel can determine whether supplementation is actually necessary.

---

Sources:

• DiNicolantonio JJ, O’Keefe JH, Wilson W (2018). Subclinical magnesium deficiency. Open Heart, 5(1), e000668.
• Wessels I, Maywald M, Rink L (2017). Zinc as a Gatekeeper of Immune Function. Nutrients, 9(12), 1286.
• Rayman MP (2012). Selenium and human health. The Lancet, 379(9822), 1256-1268.
• Prasad AS et al. (1996). Zinc status and serum testosterone levels of healthy adults. Nutrition, 12(5), 344-348.
• Thomson CD et al. (2008). Brazil nuts: an effective way to improve selenium status. American Journal of Clinical Nutrition, 87(2), 379-384.
• Willis MS et al. (2005). Zinc-induced copper deficiency: a report of three cases initially recognized on bone marrow examination. American Journal of Clinical Pathology, 123(1), 125-131.