All the Vitamins and What They Do: A Comprehensive Guide to Vitamin Functions
Vitamin A 🥕👁️
Vitamin A is a fat-soluble nutrient that quietly supports sharp vision, a resilient immune system, and healthy cellular differentiation. When you think about keeping your eyes and skin in top shape, you’re thinking about the everyday work of vitamin A and its metabolites. This section breaks down what it does, how much you need, and where you can reliably find it in foods.
Roles
Vision support is one of the most well-known roles, with retinal forms contributing to normal retina function and dark adaptation. Beyond sight, vitamin A helps regulate gene expression and supports immune defense by maintaining mucosal barriers and modulating immune cell activity.
Adequate vitamin A acts as a regulator for growth and repair, particularly in rapidly renewing tissues; see health vitamins: a comprehensive guide to choosing, using, and understanding vitamins supplements.
Experts emphasize that maintaining balance is critical: insufficient vitamin A undermines immunity and vision, but excessive intake—especially from supplements—can carry toxicity risks; for more on vitamins relevant to workouts, see good vitamins to take while working out: a comprehensive guide.
Intake and Safety
The recommended dietary allowance (RDA) for adults is roughly 900 mcg RAE/day for men and 700 mcg RAE/day for women. To prevent toxicity, atolerable upper intake level (UL) of 3000 mcg RAE is advised. Be mindful that preformed vitamin A (retinol) from supplements and animal products accumulates in the body, whereas provitamin A carotenoids from plant sources are generally much less likely to cause toxicity when eaten in a varied diet. Pregnant people should avoid high-dose retinol-containing supplements unless directed by a clinician, as excess can affect fetal development.
People at risk of deficiency include those with fat-malabsorption disorders, certain infections, and very restricted diets. In populations with limited access to animal products, plant-based carotenoids provide a valuable nutrient source when consumed with fat-containing meals to optimize absorption.
Key Food Sources
Liver (beef, chicken)—among the richest sources
Fatty fish (salmon, sardines, mackerel)
Egg yolk
Fortified dairy products (milk, yogurt) and fortified margarine
Colorful fruits and vegetables rich in beta-carotene (carrots, sweet potatoes, spinach, kale, cantaloupe)
Fortified cereals
Tip for formulating products: beta-carotene and retinyl esters offer different risk profiles; see vitamins, their functions, and sources for a concise overview.
Vitamin D ☀️🦴
Vitamin D functions as a hormone-like nutrient that influences calcium and phosphorus balance, bone health, and immune function. It can be synthesized in skin exposed to sunlight, but dietary intake and supplementation help maintain levels, especially in higher latitudes, with darker skin, or during winter.
Roles
Adequate vitamin D supports bone density and reduces the risk of certain bone-related conditions, underscoring the role of vitamins and minerals in calcium and phosphorus balance.
Emerging evidence continues to refine how much vitamin D is optimal for different populations, but consensus remains that maintaining adequate status matters for overall health and disease prevention.
Experts highlight the need to tailor vitamin D intake to individual risk factors, including sun exposure, age, body weight, and chronic conditions.
Intake and Safety
The RDA for most adults is 600–800 IU/day, with a UL of 4000 IU/day to minimize the risk of toxicity. Sun exposure and geographic location affect synthesis, while fortified foods (like dairy or cereals) and fatty fish provide dietary sources. In high-risk groups, supplementation is commonly recommended after testing and clinician guidance, to address inadequate status without overshooting.
Deficiency risk remains higher in older adults, people with limited sun exposure, and individuals with malabsorption or obesity. Conversely, excessive intake through supplements can lead to hypercalcemia and organ damage in rare cases, underscoring the importance of balancing sun, diet, and supplements appropriately.
Key Food Sources
Fatty fish (salmon, sardines, tuna)
Fortified foods (milk/dairy alternatives, cereals, orange juice)
Egg yolks
Vitamin D supplements formulated as D3 (cholecalciferol) are commonly used to correct or prevent insufficiency
Sunlight exposure contributes to endogenous synthesis, though timing and skin exposure vary by individual and season
In product development, consider stable, bioavailable vitamin D forms and packaging that protects against light and heat to preserve potency during shelf life.
Vitamin E 🫙🥜
Vitamin E is a lipid-soluble antioxidant that helps protect cell membranes from oxidative damage and supports immune function. It also plays a role in maintaining skin barrier integrity, which is of particular interest for cosmetic and dietary supplement formulations.
Roles
Antioxidant defense comes primarily from alpha-tocopherol, scavenging free radicals and helping to preserve fats in the body. This activity supports cardiovascular and skin health when consumed as part of a balanced diet. Immune modulation is another facet, with vitamin E contributing to the function of immune cells in some contexts.
In the cosmetic space, vitamin E is often valued for its stabilizing and conditioning properties in topical formulations, as well as its potential to support product shelf life when included in dietary supplements for skin health.
Intake and Safety
The RDA is 15 mg alpha-tocopherol/day, with a UL of 1000 mg/day to limit adverse effects. Most people obtain adequate amounts from a varied diet, but high-dose supplementation can disrupt vitamin K–dependent processes and interact with anticoagulant medications in some individuals, so medical supervision is advised when using high-dose products.
Excessive intake has not consistently shown additional cardiovascular benefit and may carry risks in specific populations, reinforcing the importance of targeted supplementation rather than routine megadoses.
Key Food Sources
Plant oils (wheat germ, sunflower, safflower)
Nuts and seeds (almonds, hazelnuts, sunflower seeds)
Fortified cereals
Green leafy vegetables in smaller amounts contribute to intake
fortified foods and supplements for higher, controlled dosing
For formulators, consider the stability of vitamin E in combined cosmetic and supplement products, and select forms with good bioavailability to align with clean-label expectations.
Vitamin K 🥬🥗
Vitamin K encompasses several fat-soluble compounds essential for blood clotting (K1) and bone metabolism (K2). It also benefits bone mineralization and may influence vascular health, making it relevant for both dietary planning and certain cosmetic-loading strategies that rely on nutrient synergy.
Roles
K1 (phylloquinone) is critical for activating clotting factors, preventing excessive bleeding after injuries. K2 (menaquinones) participates in bone remodeling and calcium handling, with gut bacteria contributing to circulating K2 forms. The balance of K1 and K2 activity supports coagulation and skeletal integrity together.
Emerging evidence suggests a broader role for vitamin K in vascular and bone health, though ongoing studies refine exact guidelines for different populations.
Intake and Safety
General adults aim for about 120 mcg/day for men and 90 mcg/day for women. There is no established UL for vitamin K from foods, and dietary intake is rarely associated with toxicity. Individuals on anticoagulant therapy (e.g., warfarin) should maintain consistency in vitamin K intake and consult their clinician before taking high-dose supplements that could interfere with medication.
People with fat malabsorption or certain liver conditions may need monitoring to ensure adequate absorption of fat-soluble vitamins, including K.
Key Food Sources
Leafy greens (kale, spinach, broccoli rabe)
Cruciferous vegetables (brussels sprouts, cabbage)
Natto and other fermented soy products (high in K2)
Vegetable oils (soy, canola)
Liver contains notable amounts of K1
From a formulation perspective, vitamin K’s packaging should protect from light exposure and ensure compatibility with other lipid-soluble ingredients to maintain stability in finished products.
Vitamin C 🍊🍓
Vitamin C is a water-soluble nutrient renowned for collagen synthesis, wound healing, antioxidant protection, and aiding iron absorption. It is a popular choice in both dietary supplements and topical products due to its brightening and antioxidant properties.
Roles
Collagen formation supports skin, bones, and connective tissue integrity, while antioxidant protection helps neutralize oxidative stress from daily exposures. It also enhances non-heme iron absorption, which is particularly important for individuals on plant-based diets.
Beyond structural roles, vitamin C participates in several enzymatic reactions and supports immune function. Adequate intake is associated with resilience to infections in some populations, though supplementation alone is not a substitute for other healthy lifestyle factors.
Intake and Safety
The RDA is 90 mg/day for men and 75 mg/day for women. Smokers may require higher intake due to increased oxidative stress. The UL is 2000 mg/day to minimize the risk of GI upset and kidney stone formation in susceptible individuals. Vitamin C is water soluble, and excess is typically excreted, but megadoses can cause digestive discomfort.
Most people can meet needs through a varied diet rich in fruits and vegetables. Higher-dose supplementation may be warranted for certain clinical scenarios under professional guidance, such as limited dietary intake or increased demand during illness or pregnancy.
Key Food Sources
Citrus fruits (oranges, lemons)
Berries (strawberries, raspberries)
Peppers (bell and chili peppers)
Broccoli and cruciferous vegetables
Kiwi and other fresh fruits
For products, vitamin C is often paired with ferrous iron or other antioxidants. Its stability in formulations can be pH-dependent, so formulation strategy matters for both efficacy and shelf life.
Thiamin (Vitamin B1)
Thiamin supports energy metabolism and nervous system function. Because it’s water-soluble and not stored to a large extent, regular intake from daily meals is important to prevent deficiency symptoms, which can affect energy levels and cognitive function.
Roles
Energy metabolism hinges on thiamin-containing enzymes that help convert carbohydrates into usable energy. It also contributes to nerve signaling and muscle function, making adequate intake essential for everyday stamina and performance.
Deficiency can impair nerves and the cardiovascular system if prolonged, and those with chronic alcohol use are at elevated risk due to impaired absorption and increased excretion.
Intake and Safety
The RDA is 1.2 mg/day for men and 1.1 mg/day for women. Deficiency risk rises with chronic alcohol use and poor overall nutrition. There is no UL established for thiamin because excess is typically excreted without toxicity.
Common sources include whole grains, pork, legumes, and fortified cereals. A varied diet often provides ample thiamin, particularly when combined with other B vitamins that support energy metabolism.
Key Food Sources
Whole grains (bread, cereals, brown rice)
Pork and other lean meats
Legumes (beans, lentils, peas)
Fortified cereals
Nuts and seeds contribute modest amounts
In product development, thiamin stability can be a consideration in moisture-rich formulations. Pair with stable packaging to preserve potency during shelf life.
Riboflavin (Vitamin B2)
Riboflavin participates in energy production and helps maintain skin, mucous membranes, and eye health. It’s a sensitive vitamin that can be diminished by light and heat, so careful packaging is important for supplements and functional foods.
Roles
Energy production relies on flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), which are derived from riboflavin. It also supports the health of skin and ocular surfaces, contributing to barrier integrity and visual function.
As a water-soluble vitamin, riboflavin works alongside other B vitamins to support cellular metabolism and overall energy production, especially through carbohydrate and fat pathways.
Intake and Safety
The RDA is 1.3 mg/day for men and 1.1 mg/day for women. Deficiency is uncommon but can occur with other nutritional gaps or malabsorption. There is no established UL for riboflavin because excess is typically excreted.
Food sources include milk and dairy, eggs, lean meats, and fortified cereals. Regular intake through a varied diet supports normal energy metabolism and tissue health.
Key Food Sources
Milk and dairy products
Eggs
Lean fortified cereals
Green leafy vegetables provide modest amounts
For formulation, consider riboflavin’s light sensitivity and compatibility with other antioxidants to maintain potency in multi-ingredient products.
Niacin (Vitamin B3 NAD/NADP) 🥩🥖
Niacin functions as two coenzyme forms (NAD and NADP) that are central to energy metabolism, DNA repair, and cellular signaling. It’s available in several dietary forms and has a long history in nutrition and treatment contexts.
Roles
Energy metabolism and DNA repair rely on niacin-dependent reactions, supporting cell health and metabolism, particularly in tissues with high energy demands. Niacin is also known for pharmacologic applications to manage cholesterol at high doses under medical supervision.
Dietary niacin sources commonly provide adequate intake for most people, while pharmacologic niacin requires medical oversight because of potential liver and metabolic effects at high doses.
Intake and Safety
The RDA is 16 mg NE/day for men and 14 mg NE/day for women. High-dose intake may cause flushing and other adverse effects; prolonged high-dose use can carry more serious risks, including liver concerns. There is a UL for niacin when used as a supplement for cholesterol management, to limit adverse reactions.
Food sources include meat, fish, poultry,fortified grains, and mushrooms. These form a practical basis for achieving recommended intake with a balanced diet.
Key Food Sources
Meat, fish, poultry
Fortified grains
Enriched cereals
Mushrooms provide natural niacin
In product development, ensure niacin levels are aligned with labeling guidelines and consider potential flushing when used in high amounts in combination products.
Pantothenic acid (Vitamin B5 🥑)
Pantothenic acid is a component of CoA, a central molecule in fatty acid synthesis and energy metabolism. It’s ubiquitous in foods, and deficiencies are rare, but adequate intake supports metabolic flexibility and energy production.
Roles
CoA formation underpins fatty acid synthesis and the breakdown of carbohydrates and proteins for energy. Adequate pantothenic acid supports resilience in metabolic pathways at rest and during activity.
Its broad presence in foods means most individuals easily meet needs through a varied diet, with extra attention given to diets that restrict whole foods.
Intake and Safety
The AI is 5 mg/day; there is no established UL for pantothenic acid. This reflects limited evidence of toxicity at typical intake levels. Food sources include animal products, whole grains, avocados, mushrooms, and some legumes.
Key Food Sources
Meat, poultry, fish
Whole grains and fortified cereals
Avocados
Mushrooms
Legumes and dairy in mixed diets
For product developers, pantothenic acid is typically stable in various formulations, but always validate stability with other ingredients to maintain content integrity.
Vitamin B6 (Pyridoxine)
Vitamin B6 supports amino acid metabolism and the synthesis of neurotransmitters, contributing to energy production and cognitive function. Its availability in a variety of foods makes adequate intake common, while certain populations may need targeted attention.
Roles
Amino acid metabolism and neurotransmitter synthesis are central to B6’s role in supporting mood, nerve signaling, and metabolic balance. It also participates in hemoglobin production and immune function through multiple biochemical pathways.
Because needs vary with age, sex, and physiological state, intake recommendations reflect these factors to support health across life stages.
Intake and Safety
The RDA ranges from 1.3–1.7 mg/day depending on age and sex. A UL of 100 mg/day is advised to prevent neuropathy from long-term high intake. Sources include a broad array of foods, but populations with restricted or plant-based diets should plan to include B6-rich options intentionally.
Key Food Sources
Poultry and fish
Potatoes and other starchy vegetables
Bananas and other fruits
Fortified cereals
In product development, be mindful of B6 stability in complex formulations and ensure labeling aligns with daily value guidelines for consumer clarity.
Biotin (Vitamin B7 🥚🥜)
Biotin is a carboxylation coenzyme involved in energy metabolism and fatty acid synthesis. It’s less prone to deficiency in the general population, but it remains a common component in beauty and hair-supporting supplements.
Roles
Carboxylation reactions are central to energy production and macronutrient metabolism. While rare deficiencies occur, biotin supports multiple metabolic pathways that contribute to energy and cellular function.
Biotin is often included in broad-spectrum B-complex formulations due to its wide presence in foods and favorable safety profile.
Intake and Safety
The AI is 30 mcg/day for adults; deficiency remains rare in modern diets. There is no established UL for biotin due to a lack of known toxicity at typical intake levels. Eggs, nuts, seeds, and organ meats are common sources.
Key Food Sources
Egg yolk
Organ meats
Nuts and seeds
Whole grains and some vegetables
When developing hair or beauty-focused supplements, consider consumer expectations for potency while maintaining a clean-label profile and avoiding unnecessary additives.
Folate (Vitamin B9 🟢🥬)
Folate is vital for DNA synthesis and cell division, making it especially important during pregnancy for neural tube development. It also supports red blood cell formation and overall fetal growth, as well as general cellular turnover in adults.
Roles
DNA synthesis and cell division are fundamental functions of folate. Adequate folate status prior to and during early pregnancy reduces the risk of neural tube defects. Folate also participates in methylation reactions that influence gene expression and metabolic regulation.
Folate is provided both as natural dietary folate and as synthetic folic acid in fortified foods and supplements. The folate form is more bioavailable for many individuals.
Intake and Safety
The 400 mcg DFE/day is the adults’ baseline recommendation, with higher needs during pregnancy (typically 600–800 mcg DFE/day). The UL for supplemental folate is 1000 mcg/day to prevent the masking of B12 deficiency symptoms. Food sources include leafy greens, legumes, and fortified grains.
Excess folic acid (man-made) from supplements without medical indication can obscure B12 deficiency, delaying diagnosis of potential nerve damage. Therefore, supplementation should be individualized and monitored as part of prenatal or clinical care.
Key Food Sources
Leafy greens (spinach, kale, romaine)
Legumes (lentils, chickpeas, beans)
Fortified grains and cereals
Liver contains high natural folate
For product development, ensure folate stability and correct labeling to reflect DFE equivalence, especially when combining with other B vitamins in multi-ingredient formulas.
Vitamin B12 (Cobalamin)
Vitamin B12 is essential for methylation cycles and proper nerve function. It’s primarily found in animal-derived foods, making dietary adequacy a particular focus for vegetarians and older adults who may have absorption challenges.
Roles
Nerve function and methylation cycles support energy metabolism, red blood cell formation, and neurological health. Adequate B12 status is especially important for preventing cognitive and hematologic symptoms associated with deficiency.
Absorption declines with age as intrinsic factor production may decrease, and strict vegan or vegetarian diets can raise deficiency risk if intake isn’t carefully planned with fortified foods or supplements.
Intake and Safety
The RDA is 2.4 mcg/day. There is no UL established for B12 because excess is generally excreted and not considered toxic. Rich dietary sources include animal products such as meat, dairy, and eggs; fortified foods and supplements provide reliable options for those avoiding animal products.
Older adults and individuals with absorption issues may require testing and tailored supplementation to maintain adequate blood levels and neurological function. Regular monitoring is advised in at-risk populations.
Key Food Sources
Animal-derived foods (meat, poultry, fish, dairy, eggs)
Fortified foods (plant-based milks, cereals)
Supplements to ensure adequate intake for vegetarians and older adults
For private-label formulation, B12 stability is generally favorable, but ensure packaging protects from light and heat when combined with other sensitive nutrients to preserve potency throughout shelf life.
