Micronutrient Deficiencies: The Hidden Hunger Affecting Billions

Micronutrient deficiencies—insufficient intake of vitamins and minerals—represent one of the most widespread yet underrecognized public health crises globally. The term "hidden hunger" captures the paradox: individuals may consume enough calories to meet energy needs yet remain deficient in essential micronutrients, leading to impaired development, weakened immunity, cognitive deficits, and increased mortality risk. Unlike protein-energy malnutrition with its visible wasting, micronutrient deficiencies operate silently, damaging health over years before clinical symptoms emerge.

The scale is staggering. The World Health Organization estimates that over 2 billion people—nearly one-third of the global population—suffer from at least one micronutrient deficiency. Iron deficiency alone affects approximately 1.6 billion people, making it the most common nutritional disorder worldwide. Vitamin D deficiency affects 40-50% of the global population. Iodine deficiency, once thought largely eradicated, still affects 1.8 billion people, with 270 million having goiter and 50 million having some degree of brain damage.

This comprehensive guide examines the most clinically significant micronutrient deficiencies: iron, vitamin D, vitamin B12, iodine, zinc, magnesium, and calcium. For each, we explore prevalence, physiology, deficiency symptoms, risk factors, optimal food sources, supplementation guidance, and strategies for prevention.

For related content, explore our Nutrition Hub, essential nutrients guide, and plant protein article.

🌍 1. Hidden Hunger: The Global Burden

The term "hidden hunger" was coined to describe micronutrient deficiency without overt malnutrition. An individual may have normal body weight or even obesity yet remain deficient in iron, vitamin D, B12, or other essential micronutrients. The health consequences are profound:

• Child development: Iron and iodine deficiencies during pregnancy and early childhood cause irreversible cognitive impairment. Iodine deficiency is the leading preventable cause of intellectual disability worldwide.
• Immune function: Zinc, iron, vitamin D, and vitamin A deficiencies impair immune responses, increasing susceptibility to infectious diseases. Vitamin D deficiency is associated with increased respiratory infection risk.
• Maternal and infant mortality: Iron deficiency anemia contributes to 20% of maternal deaths globally. Neural tube defects from folate deficiency remain a significant cause of infant mortality where fortification is absent.
• Chronic disease risk: Subclinical deficiencies accelerate cardiovascular disease, osteoporosis, cognitive decline, and certain cancers.
• Economic impact: The World Bank estimates that micronutrient deficiencies cost developing economies 2-3% of GDP annually through reduced productivity, healthcare costs, and lost human capital.

Why are deficiencies so common? Several factors contribute: declining soil mineral content (industrial agriculture depletes soil zinc, selenium, and iodine), highly processed diets (refining grains removes nutrients), limited dietary diversity (reliance on staple grains with few vegetables/animal products), malabsorption disorders (celiac, Crohn's, bariatric surgery), increased nutrient requirements (pregnancy, lactation, rapid growth, chronic illness), and medications that interfere with absorption or increase excretion.

🩸 2. Iron Deficiency: The Most Common Nutritional Disorder

Prevalence: 1.6 billion people globally (25% of world population). Highest in premenopausal women (30-50% prevalence in some regions), pregnant women (40-60%), children under 5 (40%), and vegetarians/vegans.

Physiology

Iron is essential for hemoglobin (oxygen transport in red blood cells), myoglobin (oxygen storage in muscle), cytochromes (cellular energy production), and numerous enzymes. The body contains 3-5g total iron: 65% in hemoglobin, 10% in myoglobin, 25% stored as ferritin and hemosiderin (liver, spleen, bone marrow), and trace amounts in enzymes. Iron balance is tightly regulated because humans have no active iron excretion mechanism; losses occur through bleeding, sweat, and sloughed cells.

Two forms of dietary iron:

• Heme iron (animal sources: red meat, poultry, fish): Absorption 15-35%, unaffected by other dietary factors.
• Non-heme iron (plant sources: legumes, spinach, fortified grains): Absorption 2-20%, enhanced by vitamin C and inhibited by phytates (grains, legumes), tannins (tea, coffee), calcium, and polyphenols.

Stages of Iron Deficiency

1. Iron depletion: Storage iron (ferritin) low, but hemoglobin normal. Asymptomatic.
2. Iron-deficient erythropoiesis: Iron supply to bone marrow inadequate; transferrin saturation low, but hemoglobin may still be normal. Fatigue, decreased exercise capacity.
3. Iron deficiency anemia (IDA): Hemoglobin falls below normal (<12 g/dL in women, <13.5 g/dL in men). Full symptom complex appears.

Symptoms of Iron Deficiency Anemia

• Fatigue, weakness, lethargy (most common)
• Pale skin and conjunctiva (pallor)
• Shortness of breath with exertion
• Heart palpitations, tachycardia
• Cold hands and feet
• Brittle, spoon-shaped nails (koilonychia)
• Hair thinning or loss
• Restless leg syndrome
• Pica: craving non-food items (ice, dirt, clay, starch)
• Impaired cognitive function, brain fog

Risk Factors

• Menstruating women: Monthly blood loss (30-80mL) requires 1-2mg daily iron absorption vs. 0.5-1mg for men.
• Pregnancy: Fetal development, placental growth, and expanded maternal blood volume require 1,000mg total iron.
• Vegetarians/vegans: Non-heme iron absorption lower; require 1.8x higher intake.
• Blood donors: Each donation removes 200-250mg iron.
• Gastrointestinal disorders: Celiac disease, Crohn's, ulcerative colitis, bariatric surgery.
• Chronic blood loss: Peptic ulcer, colon cancer, NSAID use, hemorrhoids.
• Infants and children: Rapid growth depletes maternal iron stores by 4-6 months.

Dietary Sources of Iron

Enhancing iron absorption: Pair non-heme iron foods with vitamin C (citrus, bell peppers, broccoli, strawberries). Avoid tea/coffee with meals (tannins inhibit absorption). Cook in cast iron cookware (leaches small amounts of iron).

Supplementation Guidance

For diagnosed iron deficiency: 100-200mg elemental iron daily (e.g., ferrous sulfate 325mg = 65mg elemental iron). Take on empty stomach for maximal absorption (though may cause GI side effects). Side effects: constipation, dark stools, nausea, epigastric pain. Extended-release or iron bisglycinate formulations may improve tolerability. Iron overdose is toxic—keep away from children. Recheck ferritin and hemoglobin after 3 months to normalize.

☀️ 3. Vitamin D Deficiency: The Sunlight Vitamin Crisis

Prevalence: 40-50% of global population (1 billion people). Higher in darker skin pigmentation, northern latitudes, winter months, and individuals with limited sun exposure.

Physiology

Vitamin D is unique: primarily synthesized in skin upon UVB exposure (290-315 nm), not obtained from diet. Cholecalciferol (D3) from skin/liver is hydroxylated in liver to 25-hydroxyvitamin D [25(OH)D]—the storage form measured in blood—then in kidneys to 1,25-dihydroxyvitamin D (calcitriol), the active hormone. Vitamin D receptors exist in virtually every tissue, explaining its pleiotropic effects.

Vitamin D status categories (25(OH)D levels):

• Deficient: <12 ng/mL (<30 nmol/L) — rickets/osteomalacia risk
• Insufficient: 12-20 ng/mL (30-50 nmol/L) — suboptimal for health
• Sufficient: 20-50 ng/mL (50-125 nmol/L) — optimal for bone health
• Optimal: 40-60 ng/mL (100-150 nmol/L) — preferred for immune/extra-skeletal benefits
• Toxic: >150 ng/mL (>375 nmol/L) — rare, from excessive supplementation only

Symptoms and Consequences

• Classical deficiency diseases: Rickets in children (bone deformities, growth retardation, bowing legs); osteomalacia in adults (bone pain, muscle weakness, fractures).
• Increased fracture risk: Vitamin D deficiency reduces calcium absorption, causing secondary hyperparathyroidism and bone loss.
• Immune dysfunction: Increased respiratory infections (including COVID-19 severity), autoimmune disease risk (multiple sclerosis, type 1 diabetes, rheumatoid arthritis).
• Muscle weakness: Proximal myopathy (difficulty climbing stairs, rising from chair).
• Mood disorders: Seasonal affective disorder, depression.
• Chronic disease associations: Hypertension, cardiovascular disease, type 2 diabetes, certain cancers (colorectal, breast, prostate).

Risk Factors

• Dark skin pigmentation: Melanin reduces UVB penetration; requires 5-10x longer sun exposure.
• Northern latitude: Above 37°N (e.g., Mediterranean, US Midwest, UK), UVB insufficient November-March.
• Winter season: Sun too low in sky for UVB production.
• Indoor lifestyle: Office workers, homebound elderly, hospitalized patients.
• Sun protection: SPF 30+ sunscreen blocks 95% of vitamin D production.
• Clothing coverage: Cultural/religious covering prevents synthesis.
• Obesity: Vitamin D sequestered in adipose tissue, reducing bioavailability.
• Malabsorption: Celiac, Crohn's, bariatric surgery.
• Age >65: Reduced skin synthetic capacity (by 50-75%) and kidney hydroxylation.

Dietary Sources (Limited)

Few foods naturally contain vitamin D: fatty fish (salmon: 400-600 IU/3 oz), sardines, mackerel, cod liver oil (1,300 IU/tsp), egg yolks (40 IU each), UV-exposed mushrooms (400 IU/3 oz). Fortified foods: milk (100 IU/cup), plant milks, orange juice, cereals (typically 100 IU/serving). Diet alone rarely achieves sufficient status without supplementation.

Supplementation Guidance

General population: 600-2,000 IU daily; deficient individuals: 2,000-5,000 IU daily for 3 months, then maintenance dosing. Vitamin D3 (cholecalciferol) preferred over D2 (ergocalciferol)—D3 more potent and longer-lasting. Recheck 25(OH)D after 3-6 months. Upper limit: 4,000 IU daily without monitoring; higher doses require medical supervision.

🥩 4. Vitamin B12 Deficiency: The Vegan Risk

Prevalence: 5-20% of general population, up to 80% in vegans, 20-30% in older adults, 10-15% with malabsorption.

Physiology

Vitamin B12 (cobalamin) is essential for DNA synthesis, red blood cell formation, myelin sheath maintenance, and homocysteine metabolism. B12 is unique: only synthesized by bacteria, not plants or animals. Animals obtain B12 from bacteria in their gut or contaminated feed. Thus, B12 is naturally found only in animal products. Vegans must supplement.

Absorption requires intrinsic factor (IF) produced by stomach parietal cells. B12 bound to food protein must be released by stomach acid and pepsin, bind to IF in small intestine, then absorbed in terminal ileum. Any disruption in this pathway causes deficiency.

Symptoms (Often Insidious Onset)

• Hematologic: Megaloblastic anemia (large immature red blood cells), fatigue, pallor, shortness of breath.
• Neurologic (most concerning): Peripheral neuropathy (numbness, tingling in hands/feet), gait disturbance (sensory ataxia), loss of vibration and position sense, positive Romberg sign, cognitive impairment (memory loss, confusion, "brain fog").
• Subacute combined degeneration of spinal cord: Irreversible if untreated—affects both dorsal columns (sensory) and corticospinal tracts (motor).
• Psychiatric: Depression, psychosis, mania, hallucinations (megaloblastic madness).
• Other: Glossitis (smooth, red tongue), angular cheilitis, infertility.

Risk Factors

• Vegans and strict vegetarians: No natural dietary sources; must supplement or consume fortified foods.
• Older adults (>65): Atrophic gastritis reduces stomach acid, impairing food-B12 release. Up to 30% have malabsorption.
• Pernicious anemia: Autoimmune destruction of parietal cells → no intrinsic factor → severe B12 malabsorption.
• Gastrointestinal surgery: Gastric bypass, ileal resection.
• Malabsorption disorders: Celiac, Crohn's, chronic pancreatitis.
• Medications: Proton pump inhibitors (PPIs), H2 blockers, metformin (all reduce absorption).
• Nitrous oxide (laughing gas): Inactivates B12; repeated exposure (recreational or occupational) causes deficiency.

Dietary Sources

Animal products only: clams (84 mcg/3 oz—astronomically high), beef liver (70 mcg), trout, salmon, tuna, beef, milk, yogurt, eggs (0.6 mcg each). Fortified foods: nutritional yeast (many varieties fortified), plant milks, breakfast cereals, meat substitutes (check labels).

Supplementation Guidance

Vegans: 25-100 mcg daily of cyanocobalamin (preferred form, stable) or methylcobalamin. Malabsorption: 1,000-2,000 mcg sublingual, oral, or intranasal—high-dose oral can bypass IF via passive diffusion (1% absorption). Pernicious anemia/advanced deficiency: Intramuscular B12 injections (1,000 mcg weekly until normal, then monthly). Monitor B12 levels (though serum B12 may normalize before neurologic improvement).

🧠 5. Iodine Deficiency: The Brain Development Threat

Prevalence: 1.8 billion people have insufficient iodine intake; 270 million have goiter; 50 million have some degree of iodine deficiency-related brain damage.

Physiology

Iodine is essential for thyroid hormone synthesis: thyroxine (T4) contains 4 iodine atoms; triiodothyronine (T3) contains 3. Thyroid hormones regulate basal metabolic rate, growth, and brain development. The fetal and neonatal brain is exquisitely sensitive to iodine deficiency; even mild deficiency during pregnancy reduces child IQ by 5-10 points.

Symptoms

• Goiter: Enlarged thyroid gland as pituitary overstimulates to compensate for low T4.
• Hypothyroidism: Fatigue, weight gain, cold intolerance, constipation, dry skin, hair loss, bradycardia.
• Cretinism (severe fetal deficiency): Irreversible intellectual disability, deaf-mutism, spastic diplegia, short stature—now rare in iodine-fortified regions.
• Subclinical brain damage: More common: reduced IQ, impaired school performance, lower work productivity.
• Increased pregnancy complications: Miscarriage, stillbirth, preterm birth, neonatal mortality.

Risk Factors

• Living in iodine-deficient regions: Mountainous areas (Alps, Andes, Himalayas), regions with low soil iodine (Great Lakes, UK, New Zealand).
• Non-use of iodized salt: Many countries lack mandatory iodization; use of sea salt, Himalayan salt, or gourmet salts without iodine.
• Pregnancy and lactation: Increased requirements (250 mcg daily vs. 150 mcg for non-pregnant).
• Vegans: Plant foods low in iodine unless grown in iodine-rich soil.
• Goitrogens: High intake of raw cruciferous vegetables (cabbage, kale, broccoli, cauliflower, soy) interferes with iodine uptake, but only relevant with pre-existing deficiency.

Dietary Sources

• Iodized salt: 1/4 teaspoon provides 95 mcg iodine (65% of daily needs).
• Seaweed: Very high—kelp (1,500-2,000 mcg/gram), nori (15-30 mcg/sheet), wakame. Risk of excess iodine toxicity with overconsumption.
• Seafood: Cod (100 mcg/3 oz), shrimp (35 mcg), tuna (17 mcg), sardines.
• Dairy: Milk (50-100 mcg/cup) from iodine-containing feed supplements and sanitizing solutions.
• Eggs: 25 mcg per egg.

Supplementation Guidance

Pregnant and lactating women: 150-250 mcg daily (as potassium iodide). General population: 150 mcg daily if not using iodized salt. Do not exceed 500 mcg daily without monitoring; excess iodine can cause hyperthyroidism or goiter. Note: Many prenatal vitamins lack iodine—check labels.

🛡️ 6. Zinc Deficiency: The Immune System Weakened

Prevalence: 17-20% of global population (1.2 billion people). Most common in developing countries but also common in vegetarians, older adults, and those with malabsorption.

Physiology

Zinc is a cofactor for over 300 enzymes involved in DNA synthesis, cell division, protein synthesis, wound healing, and immune function. Zinc is critical for thymic hormone production, T-cell development, and natural killer cell activity. Zinc deficiency impairs both innate and adaptive immunity.

Symptoms

• Growth retardation in children
• Delayed sexual maturation and hypogonadism
• Increased infection risk (especially respiratory and diarrheal)
• Poor wound healing
• Hair loss (alopecia)
• Acrodermatitis enteropathica (severe deficiency): skin rash around mouth and anus
• Diarrhea (zinc deficiency impairs intestinal repair)
• Impaired taste (hypogeusia) and smell
• Night blindness (zinc required for vitamin A metabolism)

Risk Factors

• Vegetarians/vegans: Plant zinc absorption inhibited by phytates; vegetarians may need 50% higher intake.
• Pregnancy and lactation: Increased requirements for fetal growth.
• Malabsorption disorders: Crohn's, celiac, chronic diarrhea.
• Liver disease: Cirrhosis impairs zinc metabolism.
• Sickle cell disease: Increased urinary zinc excretion.
• Medications: Diuretics, ACE inhibitors, penicillamine, certain antacids.

Dietary Sources

Oysters (highest: 74 mg/3 oz), beef (5 mg/3 oz), crab (4 mg), lobster (3 mg), pork (3 mg), chicken (1.5 mg), pumpkin seeds (2.2 mg/oz), cashews (1.6 mg), chickpeas (1.3 mg/cup), mushrooms (1.3 mg/cup), spinach (1.4 mg/cup).

Supplementation Guidance

For immune support during illness: 15-30 mg daily for 1-2 weeks. For treatment of deficiency: 30-50 mg daily. Upper limit: 40 mg daily. Take with food to avoid nausea. Note: High-dose zinc (>50 mg daily) for prolonged periods can cause copper deficiency (neurologic symptoms).

⚡ 7. Magnesium Deficiency: The Invisible Epidemic

Prevalence: Estimated 50-75% of Americans consume less than the RDA for magnesium. Overt deficiency (hypomagnesemia) is less common, but chronic subclinical deficiency is widespread.

Physiology

Magnesium is a cofactor for over 600 enzymes, including those involved in ATP production, protein synthesis, DNA replication, and ion transport. Magnesium is essential for muscle relaxation (calcium antagonist), nerve conduction, blood pressure regulation, and glucose metabolism.

Symptoms (Often Non-Specific)

• Muscle cramps, twitching, tremors
• Fatigue, weakness
• Insomnia, restless sleep
• Anxiety, irritability, depression
• Migraine headaches
• Constipation
• Heart palpitations, arrhythmias
• High blood pressure
• Insulin resistance

Risk Factors

• Poor dietary intake: Processed foods low in magnesium; soil depletion reduces magnesium in produce.
• Gastrointestinal disorders: Crohn's, celiac, chronic diarrhea.
• Type 2 diabetes: Hyperglycemia increases urinary magnesium excretion.
• Chronic alcoholism: Poor intake, malabsorption, increased excretion.
• Medications: Proton pump inhibitors (long-term use), diuretics, certain antibiotics, chemotherapy drugs.
• High calcium intake: Calcium supplements (without magnesium) compete for absorption.

Dietary Sources

Pumpkin seeds (156 mg/oz), chia seeds (95 mg/oz), almonds (80 mg/oz), spinach (157 mg/cup cooked), cashews (74 mg/oz), black beans (120 mg/cup), edamame (99 mg/cup), dark chocolate (64 mg/oz), avocado (58 mg each), banana (32 mg).

Supplementation Guidance

300-400 mg daily (elemental magnesium). Best absorbed forms: magnesium glycinate (gentle on stomach, good for sleep), magnesium citrate (well-absorbed, mild laxative effect), magnesium malate (good for energy/fatigue). Avoid magnesium oxide (poor absorption). Upper limit from supplements: 350 mg (higher can cause diarrhea).

🦴 8. Calcium Deficiency: Beyond Bone Health

Prevalence: Global average calcium intake 400-800 mg daily, below the RDA of 1,000-1,200 mg in most populations.

Physiology

99% of body calcium is in bones and teeth (hydroxyapatite crystals). The remaining 1% in blood and soft tissues is tightly regulated for muscle contraction, nerve transmission, blood clotting, hormone secretion, and cell signaling. When dietary calcium is insufficient, parathyroid hormone (PTH) stimulates bone resorption to maintain blood calcium, gradually depleting bone mineral density.

Symptoms and Consequences

• Osteoporosis: Low bone mass, increased fracture risk (hip, spine, wrist).
• Osteomalacia: Soft bones (with concurrent vitamin D deficiency).
• Hypocalcemia symptoms (severe deficiency): Paresthesias (tingling lips/fingers), muscle cramps, tetany, Chvostek's sign (facial twitching), Trousseau's sign (carpopedal spasm), arrhythmias.
• Dental problems: Tooth decay, periodontal disease.
• Hypertension: Calcium supplementation modestly lowers blood pressure.

Risk Factors

• Vegans and lactose intolerant: Dairy avoidance without adequate plant calcium sources.
• Older adults: Reduced calcium absorption (especially postmenopausal women).
• High sodium intake: Sodium increases urinary calcium excretion.
• High protein intake (animal protein): Increases urinary calcium, though bone effects debated.
• Vitamin D deficiency: Reduces calcium absorption from 30% to 10-15%.

Dietary Sources

Dairy: milk (300 mg/cup), yogurt (300 mg/6 oz), cheese (200-300 mg/oz). Plant sources: fortified plant milks (300 mg/cup), firm tofu made with calcium sulfate (350 mg/1/2 cup), sardines with bones (325 mg/3 oz), canned salmon with bones (180 mg/3 oz), kale (180 mg/cup cooked), collard greens (270 mg/cup), bok choy (160 mg/cup), broccoli (60 mg/cup), tahini (130 mg/2 tbsp), almonds (80 mg/oz).

Supplementation Guidance

Recommended intake: 1,000 mg daily (adults 19-50), 1,200 mg (women >50, men >70). Upper limit from supplements: 500-600 mg at a time (maximal absorption). Calcium carbonate (take with food, requires stomach acid) or calcium citrate (take anytime, better for older adults). Avoid calcium supplements if kidney stone history (consult physician).

⚠️ 9. Common Risk Factors Across Deficiencies

• Poor dietary diversity: Reliance on staple grains (rice, wheat, corn) with few vegetables, fruits, or animal products.
• Restrictive diets: Vegan (B12, iron, zinc, calcium, iodine), gluten-free (B vitamins, iron, fiber), low-carb (fiber, B vitamins, magnesium).
• Malabsorption disorders: Celiac (iron, B12, folate, D, calcium), Crohn's (multiple), bariatric surgery (B12, iron, D, calcium, copper).
• Medications: PPIs (B12, magnesium, calcium), metformin (B12), diuretics (magnesium, potassium, calcium), anticonvulsants (D, folate, biotin).
• Pregnancy and lactation: Increased requirements for iron, folate, iodine, D, calcium, zinc.
• Aging: Reduced absorption, altered metabolism, polypharmacy, reduced intake.
• Alcohol use disorder: Multiple deficiencies (B1, B12, folate, magnesium, zinc, D).

🩺 10. Diagnosis: Testing for Micronutrient Deficiencies

Recommended laboratory tests:

• Iron panel: Ferritin (best marker for iron stores), serum iron, TIBC, transferrin saturation, CBC (hemoglobin, MCV). Ferritin <30 ng/mL indicates iron depletion.
• Vitamin D: 25-hydroxyvitamin D [25(OH)D].
• Vitamin B12: Serum B12 (though normal range 200-900 pg/mL; symptoms can occur at <400). Methylmalonic acid (MMA) and homocysteine are more sensitive markers.
• Folate: RBC folate (more accurate than serum folate).
• Zinc: Serum or plasma zinc (though acute illness and inflammation affect levels).
• Magnesium: Serum magnesium (but RBC magnesium more accurate; hypomagnesemia occurs late).
• Iodine: Urinary iodine concentration (spot or 24-hour).

Note on testing: Many deficiencies can be subclinical (normal lab values but functional deficiency). Clinical suspicion should guide testing and empiric treatment in high-risk populations.

🥗 11. Prevention Strategies: Food First, Supplements Second

Dietary Diversity

Consuming a variety of whole foods is the most effective prevention strategy. The "rainbow diet"—eating vegetables and fruits of all colors—increases phytonutrient intake. Include legumes, nuts, seeds, whole grains, and if not vegetarian, lean animal products or eggs/dairy.

Food Fortification

Mandatory fortification has eliminated deficiency diseases in many countries: iodized salt (iodine deficiency), folic acid in flour (neural tube defects), vitamin D in milk (rickets), iron in cereal grains (iron deficiency). Choose fortified products when available.

Targeted Supplementation for High-Risk Groups

• All vegans: B12 (25-100 mcg daily)
• All pregnant women: Folate (400-800 mcg), iron (30 mg), iodine (150-250 mcg), D (600-2,000 IU)
• All older adults: D (800-2,000 IU), B12 (25-100 mcg if malabsorption)
• All northern latitude residents: D (600-2,000 IU October-April)

💊 12. Evidence-Based Supplementation Guide

📌 Take-Home Messages

1. Over 2 billion people suffer from micronutrient deficiencies—"hidden hunger" causing profound health consequences.
2. Iron deficiency is the most common (1.6 billion people), causing anemia, fatigue, impaired cognition, and maternal mortality.
3. Vitamin D deficiency affects 40-50% globally, increasing infection risk, bone disease, and chronic illness.
4. Vitamin B12 deficiency is universal in unsupplemented vegans and common in older adults, causing potentially irreversible neurologic damage.
5. Iodine deficiency remains the leading preventable cause of intellectual disability worldwide.
6. Zinc, magnesium, and calcium deficiencies are widespread, with non-specific symptoms often overlooked.
7. Food first: diverse whole foods, fortified products, and if needed, targeted supplementation for high-risk groups.
8. High-risk groups include vegans, pregnant women, older adults, malabsorption disorders, and those on certain medications.
9. Laboratory testing guides diagnosis, but clinical suspicion should prompt empiric treatment in high-risk populations.