Micronutrient Basics

Despite adequate intake of high-quality protein, fats, and carbohydrates, deficiencies in key micronutrients (such as magnesium, iodine, or vitamin D) can still lead to significant physiological dysfunction.

Because the body cannot synthesise most vitamins and minerals, they must be obtained through diet. While some mineral waters can provide highly bioavailable forms of these nutrients, most commercial vitamin and mineral waters are poorly formulated. They often lack sufficient concentrations, have imbalanced ratios, and frequently include sugar or artificial sweeteners to enhance taste and drive repeat consumption.

The popular conversation about micronutrients runs in two opposing directions: On one side is the idea that anyone eating a “balanced diet” gets all the micronutrients they need from food alone, and that supplementation is unnecessary marketing. On the other side (the biohacker maximalist position) is that everyone needs a 30-supplement daily stack, that subclinical deficiencies are rampant, and that aggressive supplementation extends lifespan and improves performance.

The reality is more sobering: The modern food supply has measurably less micronutrient density than the food supply of fifty years ago, due to soil depletion and selective breeding for yield over nutrition. Some deficiencies are genuinely common in modern populations (vitamin D, magnesium, iodine, B12 in vegans/vegetarians, and iron in menstruating women). Most adults benefit from targeted supplementation of one or two specific nutrients based on their actual situation, rather than a shotgun approach. The supplement industry is minimally regulated, frequently mislabeled, and market-driven. Working out which supplements you actually need, in what forms, and in what doses, requires more thinking than either extreme position allows. 

This page covers what micronutrients are, why they matter, what the most common deficiencies are, how to recognize them, and how to think about supplementation without being swept up in social media influence. The mechanisms behind macronutrient metabolism are in Macronutrient & Hydration Basics. The microbiome’s role in producing some vitamins (B12, K2) gets covered in Microbiome Basics. The light-and-vitamin-D story lives in Sunlight Exposure.

What are Micronutrients?

• Vitamins are organic compounds (containing carbon) that your body needs in small amounts but generally can’t synthesize itself. They’re mostly produced by plants, with some produced by animals or bacteria. Most vitamins serve as cofactors for enzymatic reactions; without them, specific enzymes can’t function, and the metabolic processes they catalyze break down.
• Minerals are inorganic elements (no carbon) found in soil and water, taken up by plants, then passed up the food chain. They serve structural roles (calcium and phosphorus in bone, iron in hemoglobin, sodium in extracellular fluid) and functional roles (cofactors for enzymes, electrolytes for nerve signaling, components of hormones).
• Trace elements are minerals needed in extremely small amounts – typically less than 100mg daily, sometimes just micrograms. Their effects are often disproportionate to their quantity; a few micrograms of iodine difference can determine whether thyroid function is normal or impaired.

The fundamental challenge with micronutrients is that bioavailability matters as much as content. The vitamin C in a fresh orange is meaningfully different from the ascorbic acid in a synthetic supplement, partly because of cofactor compounds in the whole food, partly because of differential absorption rates. The iron in spinach (non-heme iron) is absorbed at perhaps 5-10% efficiency; the iron in red meat (heme iron) is absorbed at 15-35%. Looking at “amount on the label” without considering bioavailability produces misleading conclusions.

A second critical concept: micronutrients work synergistically or antagonistically, not in isolation. Vitamin D requires magnesium for activation. Vitamin K2 directs calcium to bones rather than soft tissue. Iron absorption is enhanced by vitamin C and inhibited by calcium. Zinc and copper are antagonists; supplementing one without considering the other can produce deficiency in the antagonist. The popular framing of “I’m low in X, I’ll just supplement X” misses how often a genuine deficiency in one nutrient is downstream of inadequacy in another that’s required for proper function. 

Water-Soluble Vitamins

Water-soluble vitamins dissolve in water and are generally not stored long-term in significant amounts. Excess intake is excreted in urine. This means daily intake matters more for these than for fat-soluble vitamins, but also that mild excess is rarely harmful (with specific exceptions like B6).

The B Vitamin Complex

The B vitamins function primarily as cofactors in energy metabolism — converting food into ATP, the molecular currency of cellular energy. Most are needed in microgram-to-milligram quantities daily; deficiencies produce fatigue, cognitive symptoms, and various tissue-specific problems.

• Vitamin B1 (Thiamine): Required for converting carbohydrates into energy. Concentrated in whole grains, pork, legumes, and seeds. Severe deficiency causes beriberi (rare in modern populations); milder deficiency produces fatigue, irritability, and cardiovascular symptoms. Alcoholics are particularly at risk because alcohol metabolism depletes thiamine and impairs absorption.
• Vitamin B2 (Riboflavin): Cofactor for energy production and antioxidant function. Found in organ meats, eggs, milk, and leafy greens. Riboflavin deficiency is uncommon but possible in restrictive diets; symptoms include cracking at the corners of the mouth, sore throat, and inflamed tongue. A reasonable amount of research suggests that what’s diagnosed as iron-deficiency anemia may sometimes actually be riboflavin deficiency that interferes with iron metabolism. Testing both is reasonable when anemia doesn’t respond to iron supplementation alone.
• Vitamin B3 (Niacin): Required for energy production and DNA repair. Found in meat, fish, leafy greens, and beans. Severe deficiency causes pellagra (now rare); modern interest centers on niacin’s role in NAD+ metabolism and the popular nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) supplements. David Sinclair at Harvard has been the most prominent advocate for these supplements as longevity interventions; the underlying science on NAD+ decline with aging is legit, but the human evidence for the specific supplements producing meaningful longevity outcomes remains preliminary.
• Vitamin B5 (Pantothenic acid): Required for fatty acid synthesis and acetyl-CoA production. Found in essentially every food (pantos = “everywhere”); deficiency is essentially nonexistent in normal diets.
• Vitamin B6 (Pyridoxine). Required for amino acid metabolism, neurotransmitter synthesis, and red blood cell formation. Found in fish, poultry, potatoes, and bananas. Worth noting because B6 is one of the few water-soluble vitamins that produces toxicity at high doses. Long-term supplementation above 100mg daily can cause peripheral neuropathy. The “more is better” framing common in B-complex supplement marketing doesn’t apply here.
• Vitamin B7 (Biotin): Cofactor for fatty acid, amino acid, and glucose metabolism. Found in eggs, almonds, sweet potatoes, and organ meats. Deficiency is rare except with very high consumption of raw egg whites (which contain avidin, a biotin-binding protein). Cooking destroys avidin. Popular as a hair and nail supplement, the evidence for cosmetic benefits at supraphysiological doses is weak.
• Vitamin B9 (Folate): Required for cell division and DNA synthesis. Particularly critical during pregnancy for preventing neural tube defects. Found in leafy greens, organ meats, and legumes. Modern bread and cereal products are fortified with synthetic folic acid in many countries, which has produced both reductions in neural tube defects and concerns about unmetabolized folic acid in people with MTHFR gene variants. Methylfolate (5-MTHF) is the bioactive form and is preferred for supplementation by people with MTHFR variants. A substantial portion of the population, with higher rates in some ethnicities (Mexican, Hispanic, Italian, and Chinese populations show elevated MTHFR variant frequencies).
• Vitamin B12 (Cobalamin): Required for red blood cell formation, neurological function, and DNA synthesis. Found almost exclusively in animal products (meat, fish, eggs, and dairy). This is the classic deficiency risk for vegans and vegetarians; B12 deficiency develops slowly (the body stores 2-5 years’ worth) but can produce permanent neurological damage if untreated. Vegans should supplement reliably; even vegetarians should monitor B12 status. Older adults are also at increased risk because stomach acid (required for B12 absorption from food) declines with age. Common forms include cyanocobalamin (cheap, requires conversion), methylcobalamin (bioactive form), and adenosylcobalamin. The methyl- and adenosyl- forms are generally preferred, particularly for people with MTHFR variants.

Vitamin C (Ascorbic acid)

Required for collagen synthesis, antioxidant function, immune function, and iron absorption from plant sources. Humans (along with other primates and a few other species) lost the gene to synthesize vitamin C around 60 million years ago, which is why we need to get it from food.

Found in citrus fruits, berries, peppers, kiwifruit, and many vegetables. Severe deficiency causes scurvy, once a major problem for sailors before fresh produce on long voyages was practical, now rare except in extreme malnutrition.

The popular wellness discourse on vitamin C is heavily shaped by Linus Pauling’s advocacy for high-dose supplementation in the 1970s. Pauling’s claims that megadoses (10g+ daily) prevent cancer and treat the common cold were ahead of the evidence then and have not been fully supported by subsequent research. The reasonable modern position: aim for 200-500mg daily through food and modest supplementation; megadoses don’t appear to provide proportional benefits and produce GI side effects. Higher doses may have specific therapeutic uses (intravenous vitamin C has some research base for adjunctive cancer treatment), but routine high-dose oral supplementation isn’t well-supported by evidence.

Fat-soluble vitamins

Fat-soluble vitamins (A, D, E, K) require dietary fat for absorption and are stored in the liver and adipose tissue. This means daily intake matters less than for water-soluble vitamins, but also that toxicity is more possible. The body can’t easily excrete excess.

Vitamin A (Retinol and carotenoids)

Required for vision (particularly low-light vision), immune function, cell differentiation, and reproduction. Vitamin A comes in two forms:

• Retinol (preformed vitamin A) is found in animal products: liver, dairy, fish, egg yolks. Highly bioavailable; the body uses it directly without conversion.
• Carotenoids (provitamin A) are found in colourful plants: sweet potatoes, carrots, and leafy greens. The body converts beta-carotene and other carotenoids to retinol, but conversion efficiency varies dramatically between individuals. Genetic variants in BCMO1 (beta-carotene 15,15′-monooxygenase) significantly affect conversion efficiency; some people convert poorly even with substantial carotenoid intake, which means strict vegetarians and vegans with low conversion efficiency can develop functional vitamin A deficiency despite appearing to consume adequate provitamin A.

Liver consumption, particularly beef and chicken liver, provides extraordinarily concentrated vitamin A. Eating liver more than once or twice weekly can push intake into territory where chronic toxicity becomes possible (particularly in pregnancy, where excess vitamin A can cause birth defects). For most adults, weekly liver consumption is excellent nutrition; daily liver is potentially excessive.

Vitamin D

Technically a hormone rather than a vitamin, synthesized in skin from cholesterol when UVB light hits the skin, then converted in the liver and kidneys to the active form (calcitriol). The full sunlight-and-vitamin-D treatment lives in Sunlight Exposure where it belongs.

Quick summary for this page: vitamin D supports bone health, immune function, and probably much else; deficiency is genuinely common particularly at higher latitudes and in populations with darker skin (which produces vitamin D from sunlight more slowly); the food sources (fatty fish, fish liver oil, fortified dairy, mushrooms exposed to UV light) generally don’t provide enough for adults with limited sun exposure; supplementation is reasonable for most adults at higher latitudes through winter, with K2 (100–150 mcg of MK-7 form) and adequate magnesium for proper utilization.

The Holick/clinical-recommendations conflict-of-interest issues are covered in detail on the Sunlight Exposure page; the underlying biology of vitamin D is sound, but the specific dose recommendations from clinicians with industry ties warrant sceptical reading.

Vitamin E

Eight related compounds (alpha-, beta-, gamma-, delta-tocopherol and the corresponding tocotrienols), of which alpha-tocopherol is the most studied. Functions as a fat-soluble antioxidant, protecting cell membranes and lipoproteins from oxidative damage.

Found in nuts, seeds, leafy greens, and vegetable oils. Deficiency is uncommon in normal diets; most modern issues with vitamin E are around supplementation. High-dose alpha-tocopherol supplementation (400 IU+) was once recommended for cardiovascular health, but later research suggested potential harm at high doses; the current reasonable position is to get vitamin E through food rather than high-dose supplementation. Mixed tocopherols (capturing the full spectrum of forms) are preferable to alpha-tocopherol-only supplements when supplementation is used.

Vitamin K

Two main forms:

• Vitamin K1 (phylloquinone) is found in leafy greens. Required for blood clotting; deficiency produces excessive bleeding. Reasonable intake from leafy green consumption.
• Vitamin K2 (menaquinones, particularly MK-4 and MK-7) is found in fermented foods (natto is the richest source; smaller amounts in fermented cheeses), grass-fed dairy, organ meats, and egg yolks. Required for directing calcium to bones and teeth rather than soft tissue (arteries, kidneys). Most adults consume too little K2; the modern shift away from organ meats, fermented foods, and grass-fed dairy has reduced K2 intake substantially.

K2’s role in cardiovascular health and bone health has been a growing area of research, with the Rotterdam Heart Study showing that high K2 intake was associated with reduced cardiovascular calcification and mortality. The interaction with vitamin D matters significantly: high-dose vitamin D supplementation without adequate K2 may direct calcium incorrectly, potentially contributing to soft tissue calcification. K2 supplementation (typically 100–150 mcg of MK-7 form, often combined with vitamin D) has reasonable research support.

A small amount of K2 is produced by gut bacteria, but estimates suggest this contributes only modestly to overall K2 status. Dietary sources matter more than gut production for most people.

Macrominerals

Needed in larger amounts than trace minerals.

Calcium

Required for bone structure, muscle contraction, nerve function, and blood clotting. The standard recommendations (1000–1200 mg daily for adults) are calibrated for typical Western diets; populations with adequate vitamin D, K2, magnesium, and physical activity often maintain bone health on substantially less.

Found in dairy, leafy greens, sardines (with bones), tahini, and almonds. The dairy industry has heavily promoted dairy as the calcium source of choice; the actual research is less convinced. Some long-term cohort studies have failed to find dairy consumption protective against osteoporosis, and calcium supplementation alone (without K2 and vitamin D) has been associated with cardiovascular concerns due to misdirected calcium deposition.

The key point: calcium nutrition is as much about co-factors and lifestyle (vitamin D, K2, magnesium, weight-bearing exercise) as about calcium intake itself.

Phosphorus

Found in protein-rich foods (meat, fish, dairy, eggs) and grains. Required for bone structure (alongside calcium), cell membranes, and ATP. Deficiency is essentially nonexistent in modern diets; most modern populations consume too much phosphorus, particularly from phosphate additives in processed foods, which can disrupt the calcium-phosphorus balance and contribute to bone loss. The signal here is that processed food adds phosphates while removing other important nutrients. Another reason whole-food eating matters more than supplement-stack thinking.

Magnesium

Cofactor for over 300 enzymatic reactions, including ATP production, DNA synthesis, muscle function, and nervous system regulation. Deficiency is genuinely common. Estimates suggest 40–50% of US adults consume less than the RDA, and a meaningful fraction are functionally deficient.

Found in leafy greens, nuts, seeds, dark chocolate, and legumes. Modern soil depletion has reduced magnesium content of plant foods compared to a half-century ago. Bioavailability varies by form. Magnesium oxide is poorly absorbed; magnesium citrate and glycinate are well-absorbed; magnesium threonate crosses the blood-brain barrier preferentially. Different forms suit different purposes (citrate for digestion, glycinate for sleep and general use, threonate for cognitive purposes).

Symptoms of inadequacy include muscle cramps, sleep difficulty, anxiety, headaches, irregular heart rhythm, and fatigue. Supplementation at 200–400mg daily (depending on form and dietary intake) is reasonable for most adults. Higher doses produce loose stools (the digestive limit varies by individual).

Sodium and Chloride

Essential for fluid balance, nerve signaling, and digestion. The popular framing that everyone consumes too much sodium is overcalibrated for modern populations. The original studies driving low-sodium recommendations focused on people with hypertension; healthy adults. Particularly those eating whole foods, exercising, and drinking adequate water often need substantially more sodium than the standard guidelines suggest.

A reasonable approach: avoid sodium from processed foods (which comes packaged with low-quality everything else), but don’t restrict salt with whole-food meals. Active people in hot climates may benefit from supplemental electrolytes during exercise. Sodium intake substantially below 2,500–3,000mg daily has been associated with worse outcomes in some research, particularly in the absence of hypertension.

Potassium

The other main electrolyte alongside sodium, has roughly opposite effects on blood pressure. Most adults consume too little potassium relative to sodium; the historical ratio (more potassium than sodium, from a vegetable-rich diet) has reversed in modern processed-food-heavy diets. Found in vegetables, fruits, tubers, fish, dairy, and legumes.

Adequate potassium intake (4000+ mg daily) does more for blood pressure regulation than sodium restriction does. The “watch your salt” framing should probably be replaced with “increase your potassium” in most populations.

Sulfur

Found in eggs, garlic, onions, cruciferous vegetables, and meat. A component of two amino acids (methionine and cysteine) and required for connective tissue, glutathione production, and various enzymatic reactions. Deficiency is rare but can occur in restrictive diets that exclude both animal products and cruciferous vegetables.

A small fraction of people have genuine sulfur sensitivities. Symptoms can include joint pain, IBD-like symptoms, IBS, and neurotransmitter imbalances. CBS gene variants can affect sulfur metabolism. This is a legitimate clinical phenomenon for a subset of people, not the universal “everyone has hidden sulfur issues” framing some functional medicine sources promote.

Trace minerals

Trace minerals are needed in very small amounts but produce disproportionate effects when deficient.

Iron

Required for oxygen transport (hemoglobin) and cellular energy production. Two forms in food:

• Heme iron from animal products. Readily absorbed (15–35% bioavailability)
• Non-heme iron from plants. Poorly absorbed (5–10%), with absorption enhanced by vitamin C and inhibited by calcium, tannins (tea, coffee), and phytates (grains, legumes).

Iron deficiency is the most common nutrient deficiency globally, affecting roughly 30% of the world’s population in some form. Particularly common in:

• Menstruating women (regular blood loss)
• Vegans and vegetarians (lower bioavailability)
• People with celiac disease, Crohn’s disease, or H. pylori infection (impaired absorption)
• Pregnant women (increased requirements)
• Endurance athletes (foot-strike hemolysis and increased turnover)

Symptoms include fatigue, pale skin, brittle nails, hair thinning, restless legs, headaches, and reduced exercise tolerance. Diagnosis requires blood testing; ferritin (storage iron) is more sensitive than hemoglobin for catching early deficiency. Many functional health practitioners aim for ferritin above 75 ng/mL; mainstream medicine often considers anything above 20–30 ng/mL “normal.” The disparity matters because subclinical iron deficiency produces meaningful symptoms long before anemia develops.

Supplementation works for some, but causes GI side effects in many people. Iron from food (red meat, organ meats, oysters, shellfish) is generally better tolerated than supplemental iron. Iron should not be supplemented without a confirmed deficiency. Iron overload is genuinely harmful, particularly for the small percentage of the population with hemochromatosis genes.

A practical caveat: a presumed iron deficiency that doesn’t respond to iron supplementation may actually be copper deficiency (copper is required for iron metabolism) or riboflavin deficiency (riboflavin is required for iron mobilization). Testing these alongside iron when supplementation isn’t working is reasonable.

Iodine

Required for thyroid hormone production. Deficiency produces goiter, hypothyroidism, and (during pregnancy) cretinism in offspring.

Iodine deficiency is genuinely common. Roughly 40% of the world’s population has inadequate intake, including substantial fractions of supposedly developed countries. The historical solution was iodized salt; modern shifts away from table salt (toward sea salt, which is not iodized) have reduced iodine intake in some populations. Found naturally in seaweed (particularly kelp/kombu), seafood, eggs from pastured chickens, and dairy from animals supplemented with iodine.

Goitrogenic foods (raw cruciferous vegetables, soy) can interfere with iodine uptake at high consumption; cooking reduces goitrogenic compounds substantially. Most people don’t need to worry about goitrogens unless they’re already iodine-deficient.

Iodine supplementation is tricky. Both deficiency and excess can disrupt thyroid function. Sudden high-dose iodine in someone deficient can trigger thyroiditis. If you suspect iodine deficiency, work with a clinician who can monitor thyroid function rather than self-supplementing aggressively.

Zinc

Required for over 300 enzymatic reactions, immune function, wound healing, taste perception, and male reproductive function. Deficiency is common in older adults (low stomach acid impairs absorption) and vegans/vegetarians (lower bioavailability from plants, plus phytates in grains and legumes that bind zinc).

Found in oysters (extraordinary concentration), red meat, pumpkin seeds, and organ meats. Deficiency symptoms include impaired immune function, slow wound healing, hair loss, loss of taste/smell, and male hypogonadism.

Zinc and copper are antagonists. Long-term zinc supplementation without copper can produce copper deficiency. Most zinc supplements include a small amount of copper for this reason; if yours doesn’t, monitor for copper status.

Selenium

Required for thyroid hormone activation, antioxidant function (glutathione peroxidase), and immune function. Soil selenium content varies dramatically by geography; populations in selenium-poor soil regions (parts of China, parts of Europe) have measurably higher rates of selenium-related conditions.

Found primarily in Brazil nuts (extraordinary concentration – 2-3 nuts daily covers requirements for most adults), seafood, organ meats, and eggs. Deficiency contributes to thyroid dysfunction, increased inflammation, and impaired immune function.

Easy to over-supplement with Brazil nuts. Selenium toxicity (selenosis) produces hair loss, brittle nails, GI symptoms, and neurological effects. A handful of Brazil nuts provides far more selenium than the RDA; tablespoon-level daily consumption is excessive.

Copper

Required for iron metabolism, connective tissue formation, neurological function, and antioxidant systems. Deficiency is uncommon in normal diets but can develop with chronic high-dose zinc supplementation.

Found in liver, oysters, dark chocolate, cashews, and sunflower seeds. Copper-zinc balance matters more than absolute copper intake for most people.

Manganese

Cofactor for several enzymes, particularly involved in carbohydrate, amino acid, and cholesterol metabolism. Found in nuts, whole grains, leafy greens, and tea. Deficiency is rare in normal diets.

Chromium

Involved in glucose metabolism. Severe deficiency is rare; supplementation has been marketed for blood sugar regulation, but evidence for benefit in non-deficient adults is weak.

Other Trace Minerals

Molybdenum, fluoride, and several others are required in tiny amounts. Standard diets generally provide adequate amounts; specific deficiencies are rare.

Common Micronutrient Deficiencies

Iron

Frequency: Common in menstruating women, vegans/vegetarians, athletes, people with GI conditions (celiac, Crohn’s), and pregnancy.

Sources: Heme iron from red meat, oysters, mussels, sardines, organ meats; non-heme iron from dark green vegetables, lentils (with vitamin C for absorption).

Symptoms: Fatigue, pale skin, brittle nails, hair loss, headaches, restless legs, exercise intolerance, cold sensitivity, and brain fog.

Caveats: Test ferritin alongside hemoglobin; functional iron deficiency exists below the standard “anemia” threshold. If iron supplementation doesn’t resolve symptoms, test copper and riboflavin.

Vitamin B12

Frequency: Common in vegans/vegetarians, older adults, people on metformin or proton pump inhibitors.

Sources: Animal products only: meat, fish, eggs, dairy. No reliable plant sources (algae and fermented foods are not adequate).

Symptoms: Fatigue, neurological symptoms (numbness, tingling, balance problems), cognitive changes, depression, pernicious anemia.

Caveats: Daily absorption is limited (~1.5–2 mcg per meal); spreading intake across multiple meals helps. Older adults may need supplementation regardless of dietary intake due to age-related absorption decline. Methylcobalamin and adenosylcobalamin are preferred to cyanocobalamin.

Vitamin D

Frequency: Very common at higher latitudes (above ~35°), in people with darker skin, in adults who spend most of their time indoors. Auckland’s latitude (37°S) puts it in the meaningfully-deficient-in-winter range for most adults.

Sources: Sunlight (primary), fatty fish, fish liver oil, mushrooms exposed to UV light, fortified dairy. Difficult to achieve adequacy from food alone.

Symptoms: Variable and non-specific: fatigue, bone pain, muscle weakness, mood changes, susceptibility to infections.

Caveats: Test 25-hydroxyvitamin D before supplementing high doses. Co-supplement with K2 (100–150 mcg of MK-7 form) and ensure adequate magnesium. Most adults benefit from 1000–2000 IU daily; higher doses warrant blood-test guidance. Full treatment in Sunlight Exposure.

Iodine

Frequency: Approximately 40% of the world’s population, including substantial fractions in countries that have moved away from iodized salt.

Sources: Seaweed (kelp/kombu, particularly rich), seafood, eggs from pastured chickens, dairy from supplemented animals.

Symptoms: Goiter, hypothyroid symptoms (fatigue, cold intolerance, weight gain, hair loss), cognitive decline, depression. Pregnancy iodine deficiency can cause cretinism in offspring.

Caveats: Both deficiency and excess disrupt thyroid function. Don’t supplement aggressively without monitoring. Raw cruciferous and soy can inhibit iodine uptake; cooking helps.

Magnesium

Frequency: Very common. Estimates suggest 40–50% of US adults consume below the RDA, with similar patterns in other developed countries due to soil depletion.

Sources: Dark leafy greens, nuts (especially almonds, cashews, pumpkin seeds), dark chocolate, legumes.

Symptoms: Muscle cramps, sleep difficulty, anxiety, headaches, irregular heart rhythm, fatigue, constipation.

Caveats: Bioavailability varies dramatically by form. Magnesium glycinate (general use, sleep), citrate (digestive support), threonate (cognitive support), all reasonable. Avoid magnesium oxide. Required for vitamin D activation and K-dependent protein function.

Zinc

Frequency: Common in older adults (low stomach acid), vegans/vegetarians (low bioavailability + phytates), people with chronic illness.

Sources: Oysters (extraordinary), red meat, pumpkin seeds, organ meats.

Symptoms: Impaired immunity, slow wound healing, hair thinning, loss of taste/smell, mood changes, hypothyroidism (zinc activates T3 receptors), and male reproductive issues.

Caveats: Long-term high-dose supplementation depletes copper. A 15:1 zinc-to-copper ratio is roughly physiological. Hypothyroidism reduces zinc absorption, creating a feedback loop.

Selenium

Frequency: Mild deficiency is common in regions with low soil selenium content.

Sources: Brazil nuts (2-3 nuts daily cover requirements), wild salmon, kidneys, mutton, egg yolks.

Symptoms: Increased inflammation, cardiovascular risk, impaired immunity, thyroid dysfunction.

Caveats: Easy to over-supplement with Brazil nuts; symptoms of selenosis include hair loss, brittle nails, and neurological effects. Important for thyroid function. Test alongside iodine if hypothyroid symptoms persist.

Vitamin K2

Frequency: Most adults are inadequate due to modern shifts away from organ meats, fermented foods, and grass-fed dairy. Antibiotic use can further reduce gut bacterial K2 production.

Sources: Natto (richest), grass-fed dairy, organ meats, egg yolks (particularly from pastured chickens), fermented foods.

Symptoms: Subtle. Directing calcium incorrectly (soft tissue calcification, arterial calcification), increases the risk of osteoporosis, dental issues, and soft tissue mineralization.

Caveats: Particularly important when supplementing vitamin D. Anticoagulation medication (warfarin) interferes with K1, but K2’s non-clotting effects continue. G6PD and thiamine are required for K recycling; deficiency in either may produce functional K deficiency.

When to Supplement

Despite the industry problems, targeted supplementation is genuinely useful in specific circumstances:

• Vitamin D for adults at higher latitudes through winter, particularly with darker skin
• Vitamin B12 for vegans, vegetarians, and older adults
• Omega-3 (EPA/DHA) for adults not eating fatty fish 2-3 times weekly
• Magnesium for adults with inadequate dietary sources or specific symptoms
• Iron for menstruating women, athletes, vegans/vegetarians (with confirmed deficiency, not blanket supplementation)
• Iodine in regions with low food iodine availability
• Zinc for older adults and vegans (with copper consideration)
• Vitamin K2 for adults on vitamin D supplementation or with limited fermented food/organ meat intake

Most adults benefit from one to four targeted supplements based on their actual situation, not a 30-supplement biohacker stack. Adding supplements indiscriminately produces interactions, antagonisms, and quality control risks that often exceed the benefits.

Why the Modern Food Supply Has Less Micronutrient Density

A consequential trend: the same fruits and vegetables today contain measurably less micronutrient content than they did fifty years ago. The 2004 Davis et al. study at the University of Texas analyzed historical USDA nutrient data and found systematic declines in protein, calcium, phosphorus, iron, riboflavin, and vitamin C across forty-three garden crops between 1950 and 1999. Subsequent research has extended these findings.

The drivers are multiple and overlapping:

• Soil depletion: Industrial agriculture has reduced soil mineral content through repeated cropping without replenishment of trace minerals. Modern fertilizer focuses on the macronutrients plants need to grow (nitrogen, phosphorus, potassium) rather than the trace minerals that determine the nutritional density of the resulting food.
• Selective breeding for yield: Crops have been bred for size, transportability, shelf life, and pest resistance, not for nutritional density. The dilution effect: bigger crops with the same total nutrient uptake have lower nutrient concentration per unit weight.
• Picking and shipping practices: Most produce is picked before peak ripeness and ripens in transit. Many micronutrients (particularly vitamin C and various polyphenols) accumulate during the final ripening stages of the plant. Picking early reduces final nutrient content.
• Storage and processing: Time and temperature both degrade many micronutrients. The strawberry shipped from Mexico in January has substantially less vitamin C than the strawberry picked in season locally.
• Glyphosate exposure: This deserves direct treatment. Glyphosate (the active ingredient in Roundup and many other herbicides) is now the most heavily used herbicide globally, with usage having increased roughly 15-fold since GMO-tolerant crops were introduced in 1996. The compound is sprayed not only on Roundup-Ready GMO crops but also as a desiccant on non-GMO grain crops (wheat, oats, barley) shortly before harvest, dramatically increasing residue levels in the final food product.

The IARC (the WHO’s cancer research agency) classified glyphosate as “probably carcinogenic to humans” in 2015 based on Group 2A evidence. Bayer-Monsanto has paid out billions in legal settlements related to glyphosate-induced non-Hodgkin’s lymphoma cases since 2018, with total exposure exceeding $11 billion in disclosed settlements through 2023. Multiple jury verdicts have found the company liable; internal documents released through discovery showed efforts to suppress unfavorable research and influence regulatory bodies. Beyond the cancer concerns, glyphosate has been shown to disrupt soil microbial communities and chelate trace minerals (which is part of why glyphosate-treated crops have measurably lower mineral content).

The Practical Implication

The micronutrient adequacy you can achieve from a “balanced diet” today is meaningfully harder to achieve than the same goal would have been fifty years ago. This doesn’t justify the kitchen-sink supplement approach, but it does explain why many people eating reasonably good diets still have functional deficiencies.

Practical responses:

• Source higher-quality food where possible: Organic, local, in-season produce has measurably higher micronutrient density than the industrial alternative
• Eat whole-animal products: Organ meats, bone broth, properly raised dairy, wild-caught fish. These capture nutrient profiles that have changed less than the produce supply
• Diversify food sources: Eating the same 10 foods on rotation produces different deficiencies than eating 50 foods rotating through the year
• Supplement strategically: Based on identified inadequacies rather than blanket recommendations
• Recognize that perfect adequacy is hard: Some micronutrient gap is realistic for most adults; the goal is keeping it small enough that the triage theory’s downstream effects (DNA damage, accelerated aging, reduced resilience) stay manageable

Recommended and Upper Limits

The standard reference numbers, with the caveat that RDAs are calibrated to prevent deficiency in 97.5% of healthy adults under normal conditions. They’re minimums, not optimums. Optimal intake for an active adult, an older adult, a pregnant woman, or someone with specific health conditions may be substantially different.

A significant note on the sodium guideline: the upper limit of 2,300mg is widely contested in the contemporary research. James DiNicolantonio’s work on sodium has argued that the optimal range for healthy adults is closer to 3,000–6,000mg daily, and that intakes below 2,500mg may be associated with worse cardiovascular outcomes in some populations. The official limits remain conservatively calibrated for hypertensive populations rather than healthy active adults. For most readers, the practical guidance is: minimize processed-food sodium (which comes packaged with low-quality everything else); don’t fear adequate salt with whole-food meals; consider electrolyte supplementation around exercise.

For a more in-depth exploration and assessment of specific micronutrients and their interactions, see the Micronutrient Cheat Sheet.