A Complete Overview of Vitamins and Minerals: Functions, Sources, and Deficiency Risks
Key Takeaways
- Vitamins and minerals are essential micronutrients that support virtually every physiological process.
- Fat-soluble vitamins (A, D, E, K) can accumulate in the body; excess intake carries toxicity risk.
- Water-soluble vitamins must be replenished regularly through diet or supplementation.
- Deficiency risks are higher for specific groups including older adults, pregnant individuals, and those with restrictive diets.
- Whole foods generally provide micronutrients in combinations the body absorbs most effectively.
- Always consult a qualified healthcare professional before starting any supplement regimen.
Why Vitamins and Minerals Matter
Vitamins and minerals are micronutrients — substances the body requires in relatively small amounts but absolutely cannot do without. Unlike macronutrients (carbohydrates, proteins, and fats), they provide no calories, yet they are indispensable: they regulate metabolism, support immune function, maintain structural tissues, and enable the nervous system to communicate. Without adequate micronutrient intake, even a calorie-sufficient diet can lead to measurable health consequences over time.
There are 13 recognized essential vitamins and over 20 minerals considered necessary for human health. Each has a distinct biochemical role, and most cannot be synthesized in sufficient quantities by the body itself — they must come from food or, when dietary intake falls short, from supplements. To understand how supplements fit into the broader picture, see our overview of how dietary supplements work.
1 in 3
U.S. adults with vitamin D insufficiency
According to the National Institutes of Health Office of Dietary Supplements, vitamin D inadequacy is among the most common micronutrient shortfalls in American adults.
2 billion
People affected by micronutrient deficiency globally
The World Health Organization estimates that micronutrient deficiencies — particularly iron, iodine, and vitamin A — affect approximately 2 billion people worldwide.
~50%
U.S. adults using at least one dietary supplement
Centers for Disease Control and Prevention surveillance data consistently show roughly half of American adults report regular supplement use.
Fat-Soluble Vitamins: A, D, E, and K
Fat-soluble vitamins are absorbed alongside dietary fats and stored in liver tissue and adipose (fat) cells. Because they accumulate, both chronic deficiency and prolonged excessive intake are clinically meaningful concerns.
- Vitamin A — Supports vision (especially low-light), immune defense, and cell differentiation. Found in liver, dairy, eggs, and as beta-carotene in orange and dark-green vegetables. Deficiency is a leading cause of preventable childhood blindness globally.
- Vitamin D — Critical for calcium absorption, bone mineralization, and immune modulation. Synthesized in skin exposed to UVB sunlight; also present in fatty fish, fortified dairy, and egg yolks. Deficiency is widespread, particularly among people with limited sun exposure.
- Vitamin E — Acts primarily as a fat-soluble antioxidant protecting cell membranes. Found in nuts, seeds, vegetable oils, and leafy greens. Isolated deficiency is uncommon in healthy adults eating varied diets.
- Vitamin K — Essential for blood clotting (K1, phylloquinone) and bone protein activation (K2, menaquinone). K1 is abundant in leafy greens; K2 is found in fermented foods and some animal products.
Fat-Soluble Vitamins Can Accumulate to Toxic Levels
Because vitamins A, D, E, and K are stored in body fat and the liver, taking high-dose supplements over time can lead to toxicity — a risk that does not apply in the same way to water-soluble vitamins. Vitamin A toxicity, for instance, can cause liver damage and bone thinning. Do not exceed the Tolerable Upper Intake Level for any fat-soluble vitamin without explicit guidance from a healthcare provider.
Water-Soluble Vitamins: C and the B Complex
Water-soluble vitamins dissolve in water and are not stored appreciably by the body, meaning regular dietary intake is necessary. Excess amounts are typically excreted in urine, which lowers — but does not eliminate — toxicity risk.
- Vitamin C (ascorbic acid) — Cofactor for collagen synthesis, potent antioxidant, and enhancer of non-heme iron absorption. Found in citrus fruits, bell peppers, broccoli, and strawberries. Severe deficiency causes scurvy.
- B1 (Thiamine) — Converts carbohydrates to energy; supports nerve function. Found in whole grains, legumes, and pork.
- B2 (Riboflavin) — Enables oxidative energy metabolism. Found in dairy, eggs, and fortified grains.
- B3 (Niacin) — Participates in over 400 enzymatic reactions involving energy metabolism. Found in poultry, fish, peanuts, and fortified cereals.
- B5 (Pantothenic acid) — Needed for coenzyme A synthesis and fatty acid metabolism. Widely distributed in food; deficiency is rare.
- B6 (Pyridoxine) — Involved in amino acid metabolism and neurotransmitter synthesis. Found in poultry, fish, potatoes, and bananas.
- B7 (Biotin) — Supports fatty acid synthesis and gluconeogenesis. Found in eggs, liver, and nuts.
- B9 (Folate/Folic acid) — Essential for DNA synthesis and cell division; critically important in early pregnancy to reduce neural tube defect risk. Found in leafy greens, legumes, and fortified grains.
- B12 (Cobalamin) — Required for myelin sheath maintenance and red blood cell formation. Found almost exclusively in animal products; supplementation is particularly important for people following vegan diets.
Pair plant-based iron sources with vitamin C–rich foods at the same meal to meaningfully improve absorption. A squeeze of lemon juice over lentils, for example, can nearly double iron uptake.
Non-heme iron from plants is inherently less bioavailable than heme iron from meat; ascorbic acid converts ferric iron to the more absorbable ferrous form, a well-established dietary strategy.
If you take a B12 supplement, a lower-dose daily form is generally considered to be absorbed more efficiently than a single high-dose weekly pill — discuss the option with your provider.
B12 absorption relies partly on intrinsic factor, a stomach protein with limited capacity; more frequent lower doses use passive diffusion more effectively when intrinsic factor becomes saturated.
Essential Minerals: Macro and Trace
Minerals are inorganic elements obtained from food and water. Macrominerals are required in larger daily amounts; trace minerals are needed in smaller quantities but are no less essential.
Key Macrominerals
| Mineral | Primary Role | Major Food Sources |
|---|---|---|
| Calcium | Bone and tooth structure, muscle contraction, nerve signaling | Dairy, fortified plant milks, leafy greens, sardines |
| Magnesium | Enzyme cofactor for 300+ reactions; energy production, muscle relaxation | Nuts, seeds, whole grains, dark chocolate, leafy greens |
| Phosphorus | Bone matrix, ATP energy currency, cell membranes | Meat, fish, dairy, legumes |
| Potassium | Fluid balance, nerve impulse, heart rhythm | Bananas, potatoes, beans, spinach |
| Sodium | Fluid balance, nerve and muscle function | Salt, processed foods, cured meats |
Key Trace Minerals
- Iron — Oxygen transport in hemoglobin. Heme iron (animal sources) is more bioavailable than non-heme iron (plant sources). Deficiency is the most prevalent micronutrient deficiency worldwide.
- Zinc — Immune function, wound healing, protein synthesis, and taste perception. Found in red meat, shellfish, legumes, and seeds.
- Iodine — Thyroid hormone synthesis. Found in seafood, dairy, and iodized salt.
- Selenium — Antioxidant enzyme function and thyroid metabolism. Found in Brazil nuts, seafood, and poultry.
- Copper — Iron metabolism, connective tissue formation. Found in shellfish, nuts, and organ meats.
- Manganese, Chromium, Fluoride, Molybdenum — Each plays specific enzymatic or structural roles; deficiency is uncommon in varied diets.
Recognizing and Addressing Deficiency Risks
Deficiency does not always produce obvious symptoms immediately. Sub-clinical deficiency — where body stores are depleted but clinical signs are absent — can persist for months or years before manifesting. Certain populations face elevated risk:
- Older adults: Reduced absorption of B12, D, and calcium is common due to lower gastric acid production and reduced skin synthesis of vitamin D.
- Pregnant and breastfeeding individuals: Demands for folate, iron, iodine, and choline increase substantially.
- People following plant-based diets: B12, heme iron, zinc, omega-3 fatty acids, and vitamin D warrant monitoring.
- Individuals with malabsorptive conditions (e.g., celiac disease, Crohn's disease, bariatric surgery): Multiple deficiencies can develop regardless of dietary intake.
- Those with limited sun exposure: Vitamin D status may be inadequate without dietary or supplemental sources.
Supplements Do Not Substitute for Medical Evaluation
If you suspect a nutrient deficiency based on symptoms — fatigue, brittle nails, hair loss, or persistent infections — seek evaluation from a licensed healthcare professional rather than self-treating with high-dose supplements. Some symptoms attributed to deficiency have other causes, and excessive supplementation of certain nutrients can itself cause harm.
Blood tests ordered by a healthcare provider are the reliable way to diagnose deficiency. Self-diagnosing based on symptoms alone is unreliable, as many deficiency signs overlap with other conditions.
Food First, Supplements Second
Whole foods deliver vitamins and minerals alongside fiber, phytonutrients, and secondary compounds that interact synergistically. For example, vitamin C in a meal enhances iron absorption; fat in the same meal facilitates fat-soluble vitamin uptake. These interactions are difficult to replicate in isolated supplement form.
That said, supplements fill genuine gaps — particularly for nutrients that are difficult to obtain from diet alone at certain life stages or under specific health conditions. If you are considering adding supplements to your routine, our guide to navigating supplement labels and certifications is a practical starting point.
Build a Micronutrient-Rich Plate Systematically
Aim for variety across food groups rather than relying on a single 'superfood.' Rotating protein sources (legumes, fish, poultry, dairy), including dark leafy greens several times per week, and choosing whole grains over refined ones covers a wide spectrum of vitamins and minerals without requiring supplementation for most healthy adults.
It is worth noting that micronutrient needs are not universal — age, sex, health status, genetics, and medication use all influence requirements. What constitutes adequate intake for one person may be insufficient or excessive for another. For pet owners, the same principle applies: if you're curious how micronutrient science translates to companion animals, our guide to essential cat nutrients covers species-specific requirements.
This article is for general informational and educational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before making decisions about your diet, nutrition, or supplement use.