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. It plays a central role in energy production (ATP synthesis), muscle contraction, nerve function, and protein synthesis. Without sufficient magnesium, the body cannot efficiently carry out even basic metabolic processes.

DiNicolantonio et al. (2018) estimate that up to 60% of the Western population does not meet the recommended magnesium intake. Subclinical magnesium deficiency, meaning a deficiency below the threshold for clinical diagnosis, has been associated with a variety of symptoms. These include muscle cramps, fatigue, increased stress susceptibility, and sleep disturbances.

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. It is required for immune function, wound healing, DNA synthesis, and cell division. Wessels et al. (2017) showed in a comprehensive review that zinc deficiency impairs both innate and adaptive immune responses.

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 plays a role in testosterone metabolism. Prasad et al. (1996) found that moderate zinc depletion in young men was associated with a significant decline in serum testosterone levels. However, supplementation beyond requirements in individuals with adequate zinc status showed no additional effect.

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). Despite the low requirement, it fulfils critical functions. It is a component of at least 25 selenoproteins, including the glutathione peroxidase family and thioredoxin reductase.

Rayman (2012) describes the diverse functions of selenium in a comprehensive review: it is involved in thyroid hormone conversion (T4 to T3), supports the antioxidant defence system, and plays a role in immune function. 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)
Common deficiency signs	Cramps, fatigue, restlessness	Frequent infections, slow wound healing	Thyroid problems, fatigue
At-risk groups	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:

• Confirmed deficiency: A blood test from a healthcare provider can clarify the supply status. Serum magnesium alone is not very informative, as only 1% of total body magnesium circulates in the blood.
• Increased demand: Intense exercise, pregnancy, breastfeeding, or chronic stress can increase requirements.
• Impaired absorption: Gastrointestinal conditions, certain medications, or alcohol consumption can impair nutrient absorption.
• 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.

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Sources:

• DiNicolantonio JJ, O’Keefe JH, Wilson W (2018). Subclinical magnesium deficiency: a principal driver of cardiovascular disease and a public health crisis. 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.