Today's Issue

Main Topic: The five most dangerous and most common vitamin and mineral deficiencies, what each one actually does when you run low, how to test for it, what optimal looks like, and what to take

Abstract: A 2024 Lancet Global Health study of 185 countries found deficiencies affecting billions globally across multiple micronutrients. The five most dangerous and prevalent in high-income countries are vitamin D (deficient in 25-50% of the global population, linked to cancer, cardiovascular disease, autoimmune disease, depression, and cognitive decline), vitamin B12 (affects up to 20% of older adults, causes irreversible neurological damage if untreated including peripheral neuropathy and spinal cord degeneration), magnesium (50-60% of Western populations below optimal intake, involved in 300+ enzymatic reactions, linked to anxiety, insomnia, hypertension, and insulin resistance), iron (leading cause of anemia globally, most common in women and children, impairs cognitive function and immune response before anemia appears), and vitamin K2 (distinct from K1, almost entirely absent from modern Western diets, directs calcium into bones and away from arteries, deficiency linked to arterial calcification and cardiovascular disease). Optimal ranges differ from reference ranges: for vitamin D, optimal serum 25(OH)D is 40-60 ng/mL, not the laboratory reference of 20 ng/mL. B12 deficiency can exist with serum levels in the low-normal range; methylmalonic acid (MMA) and homocysteine are more sensitive markers.

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1. Vitamin D: The Deficiency That Affects Everything 🌞🦴

Vitamin D deficiency is widespread and linked to weakened immunity, increased susceptibility to infections, and bone health problems like osteoporosis.

Low vitamin D levels have also been associated with mood disorders such as depression and anxiety.

It also regulates over 200 genes. It is technically a hormone, not a vitamin.

Vitamin D deficiency has been found to be common in patients with Parkinson's disease, Alzheimer's disease, schizophrenia, depression, anxiety disorders, dementia, and older adults with cognitive decline.

A meta-analysis reported a 2.4 times greater risk of cognitive impairment in people with low vitamin D levels versus those with adequate levels.

Who is most at risk: Anyone who works indoors, lives above 35 degrees latitude (most of Europe, the US, Canada), has darker skin, wears sunscreen consistently, or is over 40. Obesity also traps vitamin D in fat tissue, making it unavailable.

What to test: Serum 25(OH)D. Most labs flag deficiency below 20 ng/mL. Optimal function is associated with 40-60 ng/mL. Many people in the "sufficient" range are still functionally low.

What to take: 2,000-5,000 IU/day of vitamin D3, taken with a fat-containing meal. Always pair with vitamin K2 (MK-7 form, 100-200mcg/day) to direct calcium into bones and away from arteries.

2. Vitamin B12: The One That Causes Permanent Damage 🧠⚡

B12 deficiency can cause irreversible neurological damage including peripheral neuropathy and subacute combined degeneration of the spinal cord.

Irreversible. That word matters.

The body can store B12 for several years, meaning deficiency often develops gradually. By the time symptoms appear, significant damage may have already occurred.

Absorption of B12 is complex, requiring intrinsic factor, a glycoprotein secreted by gastric parietal cells, to facilitate uptake in the terminal ileum.

This is why B12 deficiency is not just about diet. Many people eating animal products regularly are still deficient because their absorption is impaired.

Who is most at risk: Vegans and vegetarians, adults over 50 (stomach acid declines with age, reducing intrinsic factor), anyone on metformin (the diabetes drug that blocks B12 absorption), and people using proton pump inhibitors long-term.

What to take: 1,000mcg/day of methylcobalamin (the active form, not cyanocobalamin).

Sublingual forms absorb well even in people with intrinsic factor deficiency. Severe deficiency may require intramuscular injections.

3. Magnesium: The Deficiency Running the Modern Epidemic 💊😴

Magnesium deficiency can affect muscle function, sleep quality, and cardiovascular health. Low magnesium levels have been linked to conditions like high blood pressure, cardiovascular disease, and anxiety disorders.

It is involved in over 300 enzymatic reactions in the human body.

An estimated 50-60% of Western populations consume less than the recommended daily amount. Modern soil depletion means food contains significantly less magnesium than it did 50 years ago. Chronic stress depletes it faster still.

Standard blood tests measure serum magnesium, which reflects only 1% of total body magnesium. A normal serum level does not mean you are replete.

Who is most at risk: Anyone under chronic stress, anyone eating a processed food diet, people with type 2 diabetes (excess glucose in urine drags magnesium with it), heavy coffee or alcohol drinkers, and athletes.

What to test: Serum magnesium is standard but insensitive. RBC magnesium (red blood cell magnesium) is a more accurate marker of actual tissue stores.

What to take: 300-400mg/day of elemental magnesium as magnesium glycinate, taken in the evening. Glycinate is the most bioavailable and best-tolerated form. Most people notice improvements in sleep and anxiety within one to two weeks.

4. Iron: The Deficiency That Steals Your Brain Before Your Blood 🩸🧠

Iron deficiency is the most common micronutrient deficiency worldwide and leads to microcytic anemia, decreased capacity for work, and impaired immune and endocrine function.

The critical point most people miss: cognitive impairment and fatigue begin before anemia develops.

Iron is essential for producing dopamine and serotonin. It is critical for myelin (the protective sheath around nerve cells). Long before your blood count drops enough to show on a test, your brain is already running below capacity.

Who is most at risk: Women of reproductive age (monthly blood loss), vegetarians and vegans (plant iron is far less absorbable than haem iron), endurance athletes, and anyone with gut inflammation or celiac disease affecting absorption.

What to test: Full iron panel: serum ferritin, serum iron, transferrin saturation, and TIBC (total iron binding capacity). Ferritin is the most important single marker. Optimal ferritin for cognitive function and energy is generally 50-100 ng/mL, not the laboratory minimum of 12-20 ng/mL.

What to take: Ferrous bisglycinate is the most tolerable form (far fewer gut side effects than ferrous sulfate). Take with vitamin C to improve absorption. Take away from coffee, tea, and calcium supplements which block absorption.

5. Vitamin K2: The One Nobody Is Testing For 🫀

Vitamin K2 is almost entirely absent from modern Western diets.

It is not the same as vitamin K1, found in leafy greens and involved in blood clotting. K2 (specifically the MK-7 form) has a completely different role: it activates proteins that direct calcium into bones and keep it out of arteries.

Without adequate K2, calcium absorbed from food or supplements deposits in soft tissue, including arterial walls, rather than bone. Arterial calcification is one of the strongest predictors of cardiovascular events. K2 deficiency quietly drives it for years without symptoms.

The best food source is natto (fermented Japanese soybeans), eaten daily in Japan. Western diets contain almost none. Grass-fed dairy and egg yolks contain small amounts.

What to test: There is no widely available standard blood test for K2 status. The practical approach is to assume deficiency if you eat a typical Western diet and supplement accordingly, especially if you are taking vitamin D3.

What to take: 100-200mcg/day of MK-7 (menaquinone-7), the long-acting form. Always paired with vitamin D3. K2 and D3 work synergistically. Taking D3 without K2 raises calcium absorption without directing it properly, which is counterproductive.

Takeaways

• Vitamin D (test: 25(OH)D, optimal 40-60 ng/mL) and vitamin B12 (test: serum B12 plus MMA and homocysteine) are the two most consequential deficiencies in high-income countries; vitamin D deficiency is linked to cancer, cardiovascular disease, depression, and a 2.4x greater risk of cognitive impairment, while B12 deficiency causes irreversible neurological damage including peripheral neuropathy and spinal cord degeneration that may be advanced before symptoms appear, and both develop silently over months to years before clinical signs emerge.

• Magnesium deficiency affects an estimated 50-60% of Western populations and drives anxiety, poor sleep, hypertension, and insulin resistance across 300+ enzymatic pathways; serum magnesium is an insensitive marker and RBC magnesium is more accurate; iron deficiency impairs cognitive function and dopamine and serotonin synthesis before anemia develops, with optimal ferritin for brain function at 50-100 ng/mL rather than the laboratory minimum of 12-20 ng/mL.

• Vitamin K2 (MK-7 form, 100-200mcg/day) is almost entirely absent from Western diets and directs calcium into bones and away from arterial walls; taking vitamin D3 without K2 raises calcium absorption without directing it properly; all five deficiencies are testable, all are correctable with the right form at the right dose, and the difference between a reference range "normal" result and an optimal result is where most people are silently losing ground.

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