Vitamins: What, Why, & Where

When we think about nutrition, it’s common to focus on macronutrients (carbohydrates, proteins, and fats) because they provide energy.

But the body also depends on another group of nutrients that are just as critical for health: micronutrients, which include vitamins and minerals. While macronutrients provide energy and structural components, micronutrients enable the biochemical processes that allow the body to use that energy and maintain health.

Vitamins are organic compounds required in small amounts that support hundreds of physiological processes in the body. They help regulate metabolism, support immune function, enable energy production, and maintain healthy tissues. Even though they don’t provide calories, vitamins play a crucial role in keeping the body functioning properly.

What Are Vitamins?

Vitamins are organic compounds that the body needs in small quantities to maintain normal physiological functions such as growth, metabolism, and cellular repair (Combs, 2012). Because the body cannot synthesize most vitamins in sufficient amounts, they must be obtained through diet (Mitra et al., 2022).

There are 13 essential vitamins recognized in human nutrition. Each vitamin has unique biological roles, but many of them work together to support metabolic pathways and overall health. They support the body by acting as:

• Cofactors and coenzymes that enable metabolic reactions

• Antioxidants that protect cells from oxidative stress

• Regulators of gene expression and cell signaling

• Support for molecules for tissue growth, repair, and immune defense

Research indicates vitamin deficiencies can impair metabolic pathways, immune responses, and cellular maintenance processes, ultimately affecting overall health and disease risk (Mitra et al., 2022; Wu et al., 2019).

Why Vitamins Are Essential for the Body

Although vitamins are required in small amounts, they are involved in the normal function of nearly every biological system in the body.

Energy Production and Metabolism

Several vitamins—particularly the B-vitamin complex—act as cofactors in metabolic pathways that convert carbohydrates, fats, and proteins into usable cellular energy (ATP).

Without these vitamins, enzymes involved in energy production (glycolysis, the tricarboxylic acid cycle, and oxidative metabolism) cannot function efficiently (Huskisson et al., 2007). This is one reason inadequate vitamin intake can contribute to fatigue and lower metabolism.

Immune Function

Many vitamins play important roles in both innate and adaptive immune responses. Research consistently shows that adequate micronutrient status is necessary for optimal immune defense and resistance to infection (Gombart et al., 2020; Elmadfa & Meyer, 2019). For example:

• Vitamin A supports the structural integrity of epithelial tissues and helps regulate immune cell activity. (El-Zayat et al., 2019)

• Vitamin C supports immune cell function, antioxidant defense, and regulation of the inflammatory response. (Maggini et al., 2007)

• Vitamin D helps regulate immune signaling and antimicrobial peptide production. (Schwalfenberg, 2010)

Cellular Protection and Longevity

Many vitamins function as antioxidants that protect cells from oxidative stress and damage. Oxidative stress contributes to aging and the development of chronic diseases such as cardiovascular disease, metabolic disorders, and neurodegeneration. Vitamins such as vitamin C and vitamin E help neutralize reactive oxygen species and support cellular integrity. (Mitra et al., 2022)

Types of Vitamins

Vitamins are classified based on how they are absorbed, transported, and stored in the body. They are typically divided into two categories: fat-soluble and water-soluble.

Fat-Soluble Vitamins

Fat-soluble vitamins dissolve in dietary fat and can be stored in body tissues, particularly in the liver and adipose tissue. Because they can be stored in the body, these vitamins do not need to be consumed every day, but adequate dietary intake is still necessary over time. These include:

• Vitamin A

• Vitamin D

• Vitamin E

• Vitamin K

Key roles:

• Vitamin A: vision, immune function, skin health

• Vitamin D: calcium metabolism, bone health, immune regulation

• Vitamin E: antioxidant protection of cell membranes, immune support

• Vitamin K: blood clotting, bone metabolism

Water-Soluble Vitamins

Water-soluble vitamins dissolve in water and are not stored extensively in the body, meaning they need to be consumed more regularly. Water-soluble vitamins are heavily involved in metabolic and neurological processes, making them vital for optimal health.

These include:

• B-complex vitamins

  • B1 (Thiamin)

  • B2 (Riboflavin)

  • B3 (Niacin)

  • B5 (Pantothenic acid)

  • B6 (Pyridoxine)

  • B7 (Biotin)

  • B9 (Folate)

  • B12 (Cobalamin)

• Vitamin C

Key roles:

• Vitamin B1: energy metabolism, nerve function, carbohydrate metabolism

• Vitamin B2: energy production, antioxidant defense, cellular growth

• Vitamin B3: energy metabolism, DNA repair, nervous system support

• Vitamin B5: coenzyme A production, fatty acid metabolism, hormone synthesis

• Vitamin B6: amino acid metabolism, neurotransmitter production, RBC formation

• Vitamin B7: fatty acid synthesis, carbohydrate and amino acid metabolism

• Vitamin B9: DNA synthesis, cell division, fetal development

• Vitamin B12: RBC formation, nervous system health, DNA synthesis

Vitamin Comparison Chart (Functions and Food Sources)

Below is a quick overview of major vitamins, their primary functions, and common food sources:

Vitamin	Major Functions in the Body	Vitamin-Dense Food Sources
Vitamin A	Vision (retinal function), immune regulation, skin and epithelial tissue health, cellular growth	Liver, eggs, dairy, carrots, sweet potatoes, pumpkin, spinach, kale
Vitamin B1 (Thiamine)	Energy metabolism, nerve function, carbohydrate metabolism	Whole grains, pork, legumes, seeds
Vitamin B2 (Riboflavin)	Energy production, antioxidant defense, cellular growth	Dairy, eggs, lean meats, almonds, mushrooms
Vitamin B3 (Niacin)	Energy metabolism, DNA repair, nervous system support	Poultry, fish, beef, peanuts, whole grains
Vitamin B5 (Pantothenic Acid)	Coenzyme A production, fatty acid metabolism, hormone synthesis	Chicken, eggs, avocados, mushrooms, whole grains
Vitamin B6 (Pyridoxine)	Amino acid metabolism, neurotransmitter production, red blood cell formation	Poultry, fish, potatoes, bananas, chickpeas
Vitamin B7 (Biotin)	Fatty acid synthesis, metabolism of carbohydrates and amino acids	Eggs, nuts, seeds, salmon, sweet potatoes
Vitamin B9 (Folate)	DNA synthesis, cell division, fetal development	Leafy greens, lentils, beans, asparagus, citrus
Vitamin B12 (Cobalamin)	Red blood cell formation, nervous system health, DNA synthesis	Meat, fish, shellfish, dairy, eggs
Vitamin C	Antioxidant protection, collagen synthesis, immune function, iron absorption	Citrus fruits, strawberries, bell peppers, broccoli, kiwi
Vitamin D	Calcium absorption, bone health, immune regulation, muscle function	Fatty fish, egg yolks, fortified dairy, sunlight exposure
Vitamin E	Antioxidant protection of cell membranes, immune support	Almonds, sunflower seeds, avocado, spinach
Vitamin K	Blood clotting, bone metabolism	Kale, spinach, broccoli, Brussels sprouts

While supplements can help correct deficiencies, a diverse diet rich in whole foods remains the most reliable way to obtain a full spectrum of vitamins, because these foods also provide fiber, minerals, phytonutrients, and other bioactive compounds that support optimal health.

Signs of Vitamin Deficiency

Vitamin deficiencies can affect multiple systems in the body. In many cases, symptoms develop gradually and may initially be subtle. Below are some common clinical signs associated with inadequate vitamin intake.

Vitamin	Possible Signs of Deficiency
Vitamin A	Night blindness, dry skin, impaired immune response
Vitamin B1	Fatigue, irritability, nerve dysfunction
Vitamin B2	Cracked lips, sore throat, skin inflammation
Vitamin B3	Fatigue, digestive disturbances, skin rash
Vitamin B6	Anemia, depression, confusion
Vitamin B9	Megaloblastic anemia, fatigue, poor fetal development in pregnancy
Vitamin B12	Neurological symptoms, anemia, memory problems
Vitamin C	Fatigue, poor wound healing, bleeding gums
Vitamin D	Bone weakness, muscle weakness, impaired immune function
Vitamin E	Neuromuscular problems, impaired immune function (rare)
Vitamin K	Excessive bleeding or bruising

It is important to note that many symptoms associated with vitamin deficiencies are non-specific, meaning they can also occur in other health conditions. Laboratory testing and dietary assessment are often needed to confirm deficiencies.

Food vs Supplements: The Best Way to Get Vitamins

For most people, the best way to obtain vitamins is through a diverse, nutrient-dense diet. Whole foods provide vitamins alongside other beneficial compounds, including minerals, phytonutrients, fiber, and essential fatty acids. These compounds often work synergistically, improving nutrient absorption and biological activity.

Supplements can be helpful in certain situations, like pregnancy, deficiency, or specific medical conditions, but diet should be improved first, then add supplements for support.

Practical Ways to Increase Vitamin Intake

1. Prioritize diversity

Aim for 20 different plant foods per week and try introducing two new plant foods each week.

2. Eat the rainbow

Different colors contain different phytonutrients:

• Green: chlorophyll, glucosinolates, isothiocyanates, lutein, zeaxanthin, folate (B9), magnesium, iron, calcium, vitamin C & K

  • Examples: spinach, kale, broccoli, arugula, cabbage, zucchini, avocado

• Yellow: flavonoids, lutein, zeaxanthin, potassium, folate (B9), vitamin C

  • Examples: corn, yellow peppers, pineapple, bananas, yellow squash

• Orange: beta-carotene, alpha-carotene, beta-cryptoxanthin, potassium, vitamin C

  • Examples: carrots, sweet potatoes, pumpkin, mango, apricots

• Red: lycopene, anthocyanins, ellagic acid, potassium, folate (B9), vitamin C

  • Examples: tomatoes, watermelon, strawberries, raspberries, red peppers.

• Blue/purple: anthocyanins, resveratrol, flavonoids, manganese, vitamin C & K

  • Examples: blueberries, blackberries, purple cabbage, eggplant, grapes

• White/brown: allicin, quercetin, organosulfur compounds, potassium, selenium, vitamin C

  • Examples: garlic, onions, mushrooms, cauliflower

3. Master “nutrient pairing”

Some nutrients are absorbed better when consumed together, like fat with fat-soluble vitamins (A, D, E, K) or vitamin C with iron.

4. Include fermented foods

A healthy gut microbiome supports nutrient absorption. Include foods like kimchi, sauerkraut, kefir, and miso.

5. Stop peeling

The skin of fruits and vegetables is often very nutrient-dense. Instead of peeling, wash and keep the skins when possible.

6. Start steaming

Boiling water leaches nutrients. Steam or sauté preserves more nutrients.

7. Use the “sprinkle strategy”

Add small nutrient boosters like seeds, nuts, fresh herbs, and nutritional yeast to meals

Key Takeaway

Vitamins are required in small amounts, but their impact on human health is much bigger than most realize! They enable metabolic reactions, support immune defenses, protect cells from oxidative stress, and regulate many of the body’s physiological systems. Maintaining adequate vitamin intake through a balanced, nutrient-dense diet is one of the most effective ways to support long-term health and resilience.

References

El-Zayat, S. R., Sibaii, H., & Mannaa, F. A. (2019). Micronutrients and many important factors that affect the physiological functions of toll-like receptors. Bulletin of the National Research Centre, 43(1).

Elmadfa, I., & Meyer, A. L. (2019). The Role of the Status of Selected Micronutrients in Shaping the Immune Function.Endocrine, Metabolic & Immune Disorders - Drug Targets, 19(8), 1100–1115.

Gombart, A. F., Pierre, A., & Maggini, S. (2020). A Review of Micronutrients and the Immune System–Working in Harmony to Reduce the Risk of Infection. Nutrients, 12(1).

Huskisson, E., Maggini, S., & Ruf, M. (2007). The Role of Vitamins and Minerals in Energy Metabolism and Well-Being. Journal of International Medical Research, 35(3), 277–289.

Maggini, S., Wintergerst, E. S., Beveridge, S., & Hornig, D. H. (2007). Selected vitamins and trace elements support immune function by strengthening epithelial barriers and cellular and humoral immune responses. British Journal of Nutrition, 98(S1), S29–S35.

Mitra, S., Paul, S., Roy, S., Sutradhar, H., Bin Emran, T., Nainu, F., Khandaker, M. U., Almalki, M., Wilairatana, P., & Mubarak, M. S. (2022). Exploring the Immune-Boosting Functions of Vitamins and Minerals as Nutritional Food Bioactive Compounds: A Comprehensive Review. Molecules, 27(2), 555.

National Institutes of Health. (2017). Dietary Supplement Fact Sheets. Nih.gov.

Schwalfenberg, G. K. (2010). A review of the critical role of vitamin D in the functioning of the immune system and the clinical implications of vitamin D deficiency. Molecular Nutrition & Food Research, 55(1), 96–108.

Wu, D., Lewis, E. D., Pae, M., & Meydani, S. N. (2019). Nutritional Modulation of Immune Function: Analysis of Evidence, Mechanisms, and Clinical Relevance. Frontiers in Immunology, 9.