What Are Vitamins? Everything You Need to Know

Did you know that 94% of Americans don't meet their daily vitamin D requirements, 88.5% are deficient in vitamin E, and 43% don't get enough vitamin A? This silent nutritional gap could be behind that persistent fatigue, unexplained hair loss, or even more serious health issues.

Vitamins are essential nutrients your body needs to function at peak performance, but it can't produce them on its own. The good news is that with the right knowledge and smart food choices, you can ensure you're getting all these critical micronutrients.

In this comprehensive guide, you'll discover exactly what vitamins are, the 13 essential types for your health, how to identify deficiencies before they become serious problems, and the best food sources for each one. Get ready to transform your understanding of nutrition and wellness.

Summary

• What Are Vitamins and Why They're Vital
• The 2 Vitamin Groups: Water-Soluble vs Fat-Soluble
• The 13 Essential Vitamins and Their Functions
• Avitaminosis: When Deficiency Becomes Disease
• How to Identify Deficiencies Before Serious Symptoms
• Best Food Sources for Each Vitamin
• Supplementation: When It's Really Necessary
• Frequently Asked Questions
• Conclusion

What Are Vitamins and Why They're Vital for Your Health

Vitamins are organic chemical compounds required by the body to sustain basic functions and are optimally obtained by eating a balanced diet. The word "vitamin" comes from combining "vital" and "amine," coined in the early 20th century by chemist Casimir Funk, reflecting their fundamental importance to life.

Unlike macronutrients like proteins and carbs, vitamins don't provide direct energy. Instead, they act as facilitators of crucial biochemical processes. Think of them as keys that unlock essential chemical reactions in your body.

Why Your Body Doesn't Make Vitamins

The human body evolved in a way that caused it to lose the ability to synthesize most vitamins. This happened because our ancestors had abundant access to these nutrients through varied diets. Over time, the genes responsible for internal production were shut down.

Today, you can only produce two vitamins significantly: vitamin D (through sun exposure) and vitamin K (partially, by gut bacteria). All others must come from your diet or supplementation when necessary.

The Critical Functions of Vitamins

Vitamins play irreplaceable roles in your body:

Metabolism and energy: Although they don't provide calories, B vitamins help our bodies use energy-yielding nutrients like carbohydrates, fat and protein for fuel.

Immune system: Vitamins A, C, D, and E strengthen your natural defenses against infections and disease.

Bone and muscle health: Vitamin D increases calcium absorption, while K ensures this mineral is properly deposited in bones.

Cellular antioxidation: Vitamins C and E combat free radicals, protecting cells from premature aging and degenerative diseases.

Cell production: Folate and B12 are needed to help cells multiply by making new DNA.

A balanced diet provides all these vitamins, but choosing the right foods makes all the difference in your nutritional quality.

The 2 Vitamin Groups: Water-Soluble vs Fat-Soluble

Understanding the difference between these two groups is key to planning your diet correctly. The classification is based on how each vitamin is absorbed and stored by the body.

Water-Soluble Vitamins: Daily Use Required

Water-soluble vitamins like vitamin C and the B-complex vitamins must dissolve in water before they can be absorbed by the body, and therefore cannot be stored. Since they're not stored in significant amounts, you need to consume them regularly.

Key characteristics:

• Quickly absorbed by the body
• Excess eliminated through urine (doesn't cause toxicity)
• Need to be replenished daily or weekly
• Sensitive to heat and light (can be destroyed during cooking)
• Include vitamin C and all 8 B vitamins

The advantage of this group is you don't need to worry about overdosing through food. Your body simply eliminates what it doesn't use. On the flip side, the need for constant replenishment means a poor diet quickly leads to deficiency.

Food	Main Vitamins	Serving Size
Beef liver	A, B12, Folate, B2	3.5 oz
Salmon	D, B12, B6	5 oz
Whole egg	A, D, E, B2, B7	2 eggs
Almonds	E, B2	1 oz (23 nuts)

Vitamin Supplementation: When It's Really Necessary

The supplement industry is worth billions, but the truth is most people don't need them. Understanding when supplementation makes sense is crucial.

When Supplements Are Unnecessary

If you maintain a varied diet with fruits, vegetables, quality proteins, and healthy fats, you're probably getting all the vitamins you need.

Signs you don't need to supplement:

• Diverse daily diet
• Blood tests with adequate levels
• Stable energy throughout the day
• Healthy hair, skin, and nails
• Immune system responding well
• Normal wound healing

Preventive supplementation without professional guidance can do more harm than good. Some vitamins in excess interfere with others' absorption or cause toxicity.

Situations Requiring Supplementation

There are specific circumstances where supplementation is not just recommended but essential:

Pregnant and nursing women: Need folic acid (prevents birth defects), iron, and vitamin D in higher doses than normal. Deficiency can affect baby development.

Vegetarians and vegans: Must supplement vitamin B12, as it only exists in animal foods. May also need vitamin D, iron, and omega-3 (EPA/DHA).

Adults over 60: B12 absorption decreases with age due to reduced stomach acid. Also have higher risk of vitamin D deficiency from less sun exposure.

People with digestive diseases: Those with Crohn's disease, celiac disease, atrophic gastritis, or who've had bariatric surgery have trouble absorbing vitamins. Need supervised supplementation.

Alcoholics: Alcohol severely impairs absorption of vitamins B1, B6, folic acid, and B12. Supplementation is an essential part of treatment.

People on certain medications: Long-term antacids reduce B12. Anticonvulsants decrease folic acid. Statins can reduce coenzyme Q10.

How to Supplement Correctly

If you need to supplement, follow these guidelines for maximum effectiveness:

Get tested first: Never start supplementation without knowing your actual levels. Blood tests show exactly what's lacking.

Respect doses: More isn't better. Follow healthcare professional recommendations. Megadoses can cause toxicity.

Combine with proper diet: Supplements complement, don't replace real food. Continue prioritizing whole foods.

Take at the right time: Fat-soluble vitamins (A, D, E, K) should be taken with meals containing fat. B-complex and C vitamins can be taken on an empty stomach.

Watch for interactions: Calcium impairs iron absorption. Vitamin C increases iron absorption. Magnesium improves vitamin D absorption.

For those who train intensely and seek the best supplements, focus should be first on meeting basic vitamin needs before adding performance supplements.

Signs Your Supplementation Is Working

After 4 to 8 weeks of proper supplementation, you should notice:

• Progressive increase in energy and vitality
• Better sleep quality
• Hair and nails growing stronger
• Healthier-looking skin
• Fewer colds and infections
• Better recovery after workouts

If there's no improvement after 2 months, reassess with your professional. There may be absorption problems or incorrect diagnosis.

Fat-Soluble Vitamins: Long-Term Storage

Fat-soluble vitamins like A, D, E, and K dissolve in fat and tend to accumulate in the body. They're stored in the liver and fatty tissue, creating reserves that can last months or even years.

Key characteristics:

• Require bile and fats for proper absorption
• Stored in liver and fatty tissue
• Can accumulate and cause toxicity if consumed in excess
• More stable to heat and cooking
• Include vitamins A, D, E, and K

The big benefit is you don't need to consume them daily. A diet rich in these vitamins creates sufficient reserves for periods of low intake. However, the risk of hypervitaminosis (excess) exists, especially with improper supplementation.

Important tip: If you follow a low-fat diet, you might have trouble absorbing these vitamins. Always include a healthy fat source in meals, like extra virgin olive oil, avocado, or nuts.

The 13 Essential Vitamins and Their Functions in the Body

There are exactly 13 vitamins recognized as essential for human health. Each has specific and irreplaceable functions. Let's get to know all of them.

Vitamin A (Retinol): The Vision and Immunity Vitamin

Vitamin A is crucial for eye health, a strong immune system, and proper cell renewal. It exists in two forms: retinol (animal origin) and beta-carotene (plant origin, which your body converts to vitamin A).

Main functions:

• Production of rhodopsin, essential pigment for night vision
• Maintenance of skin and mucous membrane integrity
• Immune system strengthening
• Cell growth and differentiation

Deficiency causes: Night blindness, dry and flaky skin, increased susceptibility to infections, impaired growth in children.

Best sources: Beef liver, carrots, sweet potato, spinach, mango, egg yolk, pumpkin.

Daily recommended amount: 700-900 mcg for adults.

B-Complex Vitamins: The Metabolism Fuel

The B complex encompasses 8 different vitamins, each with specific but complementary functions. All actively participate in energy metabolism.

Vitamin B1 (Thiamin): Neural Energy

Thiamin is an essential water-soluble vitamin that acts as a coenzyme in carbohydrate and branched-chain amino acid metabolism. Its severe deficiency causes beriberi, a disease affecting the heart and nervous system.

Sources: Pork, whole grains, legumes, sunflower seeds.

Daily dose: 1.1-1.2 mg.

Vitamin B2 (Riboflavin): Energy Release

Participates in cellular energy production and protects against oxidative damage. Deficiencies cause cracks at the corners of the mouth and tongue inflammation.

Sources: Milk and dairy products, eggs, lean meats, dark leafy greens.

Daily dose: 1.1-1.3 mg.

Vitamin B3 (Niacin): Cardiovascular Health

Fundamental for over 400 enzymatic reactions in the body. Helps control cholesterol and maintains skin health. Its severe deficiency causes pellagra.

Sources: Chicken, tuna, peanuts, mushrooms, liver.

Daily dose: 14-16 mg.

Vitamin B5 (Pantothenic Acid): Hormones and Antibodies

Participates in hormone production, antibody formation, and protein metabolism. Deficiency is rare.

Sources: Present in virtually all foods, especially eggs, fish, chicken, avocado.

Daily dose: 5 mg.

Vitamin B6 (Pyridoxine): Healthy Nervous System

Essential for over 100 enzymatic reactions, mainly in protein metabolism. Important for neurotransmitter production.

Sources: Salmon, chicken, banana, potato, chickpeas.

Daily dose: 1.3-1.7 mg.

Vitamin B7 (Biotin): Strong Hair, Skin, and Nails

Known as the beauty vitamin, it's essential for hair, skin, and nail health. Also participates in fat metabolism.

Sources: Egg yolk, liver, almonds, walnuts, cauliflower.

Daily dose: 30 mcg.

Vitamin B9 (Folic Acid): DNA Formation

Fundamental for DNA synthesis and blood cell formation. Extremely important during pregnancy to prevent fetal malformations.

Sources: Dark leafy greens, legumes, liver, avocado, broccoli.

Daily dose: 400 mcg (600 mcg for pregnant women).

Vitamin B12 (Cobalamin): Blood Cells and Nerves

The only vitamin containing cobalt. Essential for red blood cell formation and nervous system maintenance. Vegans have high risk of deficiency.

Sources: Exclusively from animal origin - meats, fish, eggs, milk, and dairy products.

Daily dose: 2.4 mcg.

For those who practice regular physical exercise, B complex vitamins are even more important, as they increase cellular energy demand.

Vitamin C (Ascorbic Acid): The Antioxidant Power

Vitamin C is an antioxidant that promotes healthy teeth and gums, helps the body absorb iron and maintain healthy tissue, and is essential for wound healing.

Main functions:

• Powerful antioxidant action
• Collagen synthesis for skin, bones, and blood vessels
• Increases absorption of non-heme iron (plant-based)
• Strengthens the immune system

Deficiency causes: Scurvy (bleeding gums, bruising, slow healing), chronic fatigue, increased susceptibility to infections.

Best sources: Oranges, lemons, strawberries, kiwi, bell peppers, broccoli, tomatoes.

Daily amount: 75-90 mg for adults.

Important: Vitamin C is heat-sensitive. Eat raw or lightly cooked fruits and vegetables to preserve its content.

Vitamin D (Calciferol): The Sunshine Hormone

Vitamin D is known as the "sunshine vitamin," since it is made by the body after being in the sun. Technically a hormone, vitamin D is unique because your body can produce it through sun exposure. It regulates over 200 genes and is fundamental for numerous functions.

Main functions:

• Increases calcium and phosphorus absorption for strong bones
• Modulates the immune system
• Regulates mood and prevents depression
• Protects against autoimmune diseases

Deficiency causes: Osteoporosis, rickets in children, muscle weakness, increased risk of autoimmune diseases, depression.

Sources: Sun exposure (15-20 minutes daily), fatty fish (salmon, sardines), egg yolk, sun-exposed mushrooms, fortified foods.

Daily amount: 600-800 IU (15-20 mcg).

Vitamin D deficiency is extremely common in people who work in closed environments or live in regions with little sunlight. In these cases, supplementation may be necessary.

Vitamin E (Tocopherol): Cellular Antioxidant Protection

Vitamin E is an antioxidant also known as tocopherol. It's a group of 8 fat-soluble compounds with powerful antioxidant action. It protects cell membranes against oxidative damage.

Main functions:

• Protects cells against free radicals
• Maintains cell membrane integrity
• Improves blood circulation
• Protects skin against premature aging

Deficiency causes: Neurological problems, muscle weakness, vision problems (rare in healthy people).

Best sources: Almonds, hazelnuts, sunflower seeds, wheat germ oil, avocado, spinach.

Daily amount: 15 mg.

Vitamin K: The Coagulation Vitamin

Essential for proper blood clotting and bone health. Exists in two main forms: K1 (plant origin) and K2 (produced by gut bacteria and present in fermented foods).

Main functions:

• Activates proteins responsible for blood clotting
• Directs calcium to bones (not to arteries)
• Prevents vascular calcification
• Maintains strong bones

Deficiency causes: Excessive bleeding, easy bruising, fragile bones.

Best sources: Dark leafy greens (kale, spinach, broccoli), natto (fermented soy), meats, fermented cheeses.

Daily amount: 90-120 mcg.

Vitamin	Main Function	Best Food Source
A	Vision and immunity	Liver, carrots
C	Antioxidant and collagen	Citrus fruits
D	Calcium absorption	Sun + fatty fish
E	Cell protection	Nuts and seeds

Avitaminosis: When Vitamin Deficiency Becomes Serious Disease

Avitaminosis is the medical term for total or severe vitamin deficiency. When this shortage reaches critical levels, specific diseases emerge that can have serious consequences if untreated.

Scurvy: The Sailors' Disease

Caused by severe vitamin C deficiency, scurvy was responsible for thousands of sailors' deaths between the 15th and 18th centuries. Today it's rare, but still occurs in people with very restricted diets.

Progressive symptoms:

• Bleeding gums and tooth loss
• Easy bruising
• Extremely slow wound healing
• Joint pain
• Anemia and extreme fatigue

In untreated cases, it can progress to fatal internal hemorrhaging. The good news is symptoms begin reversing in just 24 hours with proper vitamin C supplementation.

Beriberi: The Attack on the Nervous System

Result of critical vitamin B1 (thiamin) deficiency. Two types exist: wet beriberi (affects the heart) and dry beriberi (affects the nervous system).

Wet beriberi causes:

• Heart dilation and weakness
• Fluid accumulation in lungs
• Leg swelling
• Difficulty breathing

Dry beriberi causes:

• Progressive loss of muscle strength
• Tingling and numbness in extremities
• Difficulty walking
• Paralysis in severe cases

It's more common in alcoholics, as alcohol impairs thiamin absorption. Can also occur in people who consume mainly polished white rice.

Pellagra: The Disease of the 4 Ds

Caused by severe vitamin B3 (niacin) deficiency, pellagra is characterized by the "4 Ds": dermatitis, diarrhea, dementia, and death (if untreated).

Characteristic symptoms:

• Dark, scaly, rigid skin (especially in sun-exposed areas)
• Chronic diarrhea
• Tongue and mucous membrane inflammation
• Mental confusion and memory loss
• Severe depression

Pellagra was common in populations eating mainly corn not treated with lime. Today it's rare, but can occur in people with carcinoid syndrome or severe alcoholism.

Rickets: Bones That Won't Harden

Childhood disease caused by critical vitamin D and calcium deficiency. Bones don't mineralize properly, becoming soft and deformed.

Signs in children:

• Delayed growth and development
• Bowed or "X-shaped" legs
• Skull deformities
• Enlarged wrist and ankle joints
• Muscle weakness
• Delayed fontanelle closure

In adults, the equivalent version is called osteomalacia, causing chronic bone pain and frequent fractures. Prevention is simple: adequate sun exposure and diet with vitamin D.

Night Blindness and Xerophthalmia

Result of severe vitamin A deficiency. Night blindness is the first symptom, progressing to dry eyes (xerophthalmia) and, in extreme cases, permanent blindness.

Disease progression:

• Difficulty adapting in dark environments
• Dry, irritated eyes
• Whitish spots on cornea
• Corneal ulcers
• Permanent scarring leading to blindness

Vitamin A deficiency is considered a public health problem in developing countries, being one of the main causes of preventable blindness in children. In the U.S., various programs exist to ensure adequate intake, though pockets of deficiency remain.

To prevent all these serious diseases, the secret lies in maintaining a diversified and balanced diet throughout life.

How to Identify Deficiencies Before Serious Symptoms

Most vitamin deficiencies start silently, with subtle symptoms you can easily ignore or attribute to other causes. Recognizing these early signs is key to avoiding serious problems.

Persistent Fatigue That Doesn't Improve With Rest

If you sleep 8 hours a night but wake up tired, and fatigue persists even on weekends, it could be iron deficiency combined with vitamins B12, B6, or folic acid.

What to do: Get a complete blood count with ferritin, B12, and folic acid levels. Meanwhile, include lean meats, dark leafy greens, and legumes in your daily diet.

Excessive Hair Loss and Brittle Nails

Losing 50 to 100 strands daily is normal. But if you notice clumps on your pillow or the drain clogging frequently, it may indicate biotin (B7), iron, or vitamin D deficiency.

Nails that peel, break easily, or have white spots are also warning signs.

What to do: Increase consumption of eggs (especially yolk), nuts, and fish. Consider a biotin supplement after consulting with a professional.

Slow Healing and Frequent Bruising

Cuts taking more than 10 days to close or bruises appearing without apparent reason may indicate vitamin C, K, or protein deficiency.

Vitamin C is essential for collagen production, while K regulates clotting. Together, they ensure quick and efficient healing.

What to do: Increase citrus fruits, strawberries, and dark leafy greens. If the problem persists, see a doctor to investigate clotting disorders.

Night Vision Problems

If you have trouble seeing in low-light environments or your eyes take a while to adjust when entering a dark room, it could be an early sign of vitamin A deficiency.

This is one of the first symptoms to appear, well before xerophthalmia (dry eyes) or more serious problems.

What to do: Consume orange foods (carrots, pumpkin, papaya) and dark leafy greens rich in beta-carotene daily.

Frequent Muscle Cramps

Recurring cramps, especially at night, may indicate magnesium deficiency combined with vitamins D and B1. These nutrients work together for proper muscle contraction and relaxation.

What to do: Besides maintaining adequate hydration, consume bananas, avocados, nuts, and fatty fish. For those who train intensely, supplementation may be necessary.

Best Food Sources for Each Essential Vitamin

Building a colorful and varied plate is the best strategy to ensure all vitamins. Here's the definitive guide to foods rich in each nutrient.

Rainbow on Your Plate: The Color Rule

Each food color indicates different phytochemical compounds and vitamins:

Red/Orange: Rich in vitamin A (beta-carotene), C, and lycopene. Includes carrots, tomatoes, papaya, red bell peppers, pumpkin.

Dark green: Source of vitamins K, B9 (folic acid), C, and iron. Kale, spinach, broccoli, arugula, watercress are examples.

Yellow: Rich in vitamin C and antioxidants. Mango, pineapple, corn, yellow bell pepper.

Purple/Blue: Contains anthocyanins and vitamins C and K. Grapes, blueberries, eggplant, purple cabbage.

White: Source of B vitamins and minerals. Garlic, onion, cauliflower, mushrooms.

Animal Proteins: The Complete Source

Meats, fish, eggs, and dairy provide vitamins that don't exist or are poorly absorbed from plant sources:

• Beef liver: Champion in vitamin A, B12, folic acid, iron. 3.5 oz provides over 500% of daily B12 needs.
• Wild salmon: Rich in vitamin D, B12, B6, and omega-3. A 5 oz serving provides 100% of daily vitamin D.
• Eggs: Yolk contains vitamins A, D, E, K, B2, B5, B7 (biotin), and choline. One of the most complete foods.
• Fermented dairy: Natural yogurt and kefir provide B12, B2, calcium, and probiotics that help nutrient absorption.

Nuts and Seeds: Small Nutritional Giants

Despite their size, these foods pack fat-soluble vitamins and essential minerals:

• Almonds: Best source of vitamin E (1 oz provides 100% of daily needs).
• Brazil nuts: Rich in selenium and vitamin E (2 units meet daily selenium needs).
• Sunflower seeds: Source of vitamins E, B1, B6, and folic acid.
• Walnuts: Rich in omega-3, vitamin E, and B6.

Just 1 oz of mixed nuts daily provides significant amounts of vitamins E, B, and healthy fats.

Fruits: Sweet Source of Vitamins

Fruits are the best sources of vitamin C and beta-carotene:

• Oranges: Provide vitamin C, folic acid, and fiber. One medium orange meets 90% of daily vitamin C needs.
• Strawberries: Rich in vitamin C, folic acid, and antioxidants. 8 berries = 100% of vitamin C.
• Bananas: Excellent source of vitamin B6, potassium, and magnesium.
• Mangoes: Rich in vitamin A (beta-carotene), C, and E.

Legumes: Complete Plant Protein

Beans, lentils, peas, and chickpeas are fundamental for vegetarians and vegans:

• Black beans: Rich in folic acid, B1, iron, and fiber.
• Lentils: Source of B1, B6, folic acid, and iron.
• Chickpeas: Contains B6, folic acid, iron, and proteins.

One serving of legumes daily provides significant amounts of B vitamins and helps with muscle gain for those who train.

Frequently Asked Questions

What's the difference between water-soluble and fat-soluble vitamins?

Water-soluble vitamins dissolve in water and need to be consumed daily since they're not stored in the body. Fat-soluble vitamins dissolve in fat and can be stored in the liver and fatty tissue for months.

Can I get all my vitamins from food alone?

Yes, a balanced and varied diet with fruits, vegetables, legumes, proteins, and whole grains provides all necessary vitamins for most healthy people. Supplementation is only necessary in specific cases guided by healthcare professionals.

What are the most common vitamin deficiency symptoms?

Symptoms vary depending on which vitamin is lacking, but common signs include excessive fatigue, hair loss, brittle nails, night vision problems, bleeding gums, and difficulty healing wounds.

Which vitamins can't the human body produce?

The body doesn't produce vitamin C in sufficient quantities, making it essential to get from food. Most other vitamins also need to be consumed, except vitamin D (produced through sun exposure) and K (partially produced by gut bacteria).

Can I take vitamins without medical supervision?

It's not recommended. Excess vitamins, especially fat-soluble ones, can cause toxicity and health problems. It's best to get blood tests to identify real deficiencies before starting any supplementation.

How long does it take to reverse a vitamin deficiency?

It depends on the vitamin and severity of the deficiency. Mild cases can be corrected in 2 to 4 weeks with proper diet or supplementation. Severe deficiencies may take 2 to 3 months for complete normalization.

Conclusion

Vitamins are essential micronutrients your body needs to function at optimal levels. Now you know the 13 fundamental vitamins, their specific functions, and the best food sources for each one.

The good news is that maintaining adequate vitamin levels isn't complicated. A colorful, varied diet rich in whole foods provides everything you need. Supplementation only becomes necessary in specific situations like pregnancy, dietary restrictions, or particular medical conditions.

If you've identified deficiency symptoms, don't ignore your body's signals. Seek professional guidance to get proper tests and, if necessary, start correct supplementation. With the right knowledge and smart choices, you ensure health and vitality for many years to come.

Remember that understanding vitamins is just one piece of the wellness puzzle. Combine proper nutrition with regular exercise, quality sleep, and stress management for complete health optimization. Your body is an incredible machine that, when properly fueled and cared for, can perform at its absolute best.