All 13 Essential Vitamins: How Much Do We Need, and Can We Make Them Ourselves?

HealthyRetired · Food and Healthy Aging · Reference article

Vitamins are substances we need in small amounts to support normal body functions. They help with processes such as energy metabolism, tissue maintenance, blood formation and immune function. They do not themselves supply calories, and taking extra vitamins does not automatically produce extra energy.

There are 13 recognised essential vitamins: A, C, D, E and K, plus eight B vitamins. Minerals such as magnesium and calcium are also essential nutrients, but they are not vitamins.

What does a daily recommendation mean?

The tables below use the US National Academies' Dietary Reference Intakes for generally healthy adults aged 51 and over, checked against NIH fact sheets. Other countries may use somewhat different reference values or units. These are nutrition-planning values, not prescriptions for treating a deficiency. [1]

A Recommended Dietary Allowance (RDA) is designed to meet the needs of nearly all healthy people in the relevant group. An Adequate Intake (AI) is used when evidence is insufficient to establish an RDA. The AI entries are marked with an asterisk.

The amounts refer to total usual intake from food, fortified foods and supplements, rather than an amount everyone must buy in a capsule. Aim for a nutritionally adequate pattern over time; you do not need to hit every number exactly every day.

Units: 1 milligram (mg) = 1,000 micrograms (µg or mcg). Confusing the two can create a thousandfold dosing error.

The four fat-soluble vitamins

“Fat-soluble” is the usual term for what we sometimes call oil-soluble vitamins.

Vitamin	Men, 51+	Women, 51+	Main roles	Useful food sources
A	900 µg RAE	700 µg RAE	Vision, immune function, growth and maintenance of tissues	Orange sweet potato, carrots, pumpkin and leafy greens supply carotenoids; eggs and dairy supply preformed A
D	15 µg (600 IU), ages 51–70; 20 µg (800 IU), ages 71+	Same	Calcium absorption, bone health and muscle function	Oily fish, appropriately fortified foods; UV-exposed mushrooms supply D2
E	15 mg alpha-tocopherol	15 mg alpha-tocopherol	Helps protect cell membranes from oxidative damage	Sunflower seeds, almonds, hazelnuts and vegetable oils
K	120 µg*	90 µg*	Normal blood clotting and activation of proteins involved in bone metabolism	Leafy greens supply K1; natto is rich in the K2 form MK-7

RAE means retinol activity equivalents: it accounts for differences between preformed vitamin A and plant precursors. IU means international units; for vitamin D, 1 µg equals 40 IU. There is no separate established US daily requirement for K2 or MK-7. [1–4]

The vitamin D figures assume minimal sun exposure. Living somewhere sunny does not by itself establish that an individual has an adequate vitamin D level. [2]

The nine water-soluble vitamins

All eight B vitamins, plus vitamin C, belong to this group.

Vitamin	Men, 51+	Women, 51+	Main roles	Useful food sources
B1 — thiamin	1.2 mg	1.1 mg	Energy metabolism and normal nerve function	Whole grains, legumes and seeds
B2 — riboflavin	1.3 mg	1.1 mg	Energy metabolism and cellular functions	Almonds, mushrooms, dairy and suitably fortified foods
B3 — niacin	16 mg NE	14 mg NE	Components of NAD and NADP, used in metabolism	Peanuts, whole grains, mushrooms, fish and poultry; dietary protein also contributes through tryptophan
B5 — pantothenic acid	5 mg*	5 mg*	Formation of coenzyme A, important in metabolism	Mushrooms, sunflower seeds, avocado and many other foods
B6	1.7 mg	1.5 mg	Amino-acid metabolism, haemoglobin and neurotransmitter production	Chickpeas, potatoes, bananas, fish and poultry
B7 — biotin	30 µg*	30 µg*	Enzymes involved in fat, carbohydrate and amino-acid metabolism	Nuts, seeds, cooked eggs and other foods
B9 — folate	400 µg DFE	400 µg DFE	DNA synthesis, cell division and blood-cell formation	Lentils, beans, leafy greens and fortified foods
B12 — cobalamin	2.4 µg	2.4 µg	Nerve function, DNA synthesis and healthy red blood cells	Animal foods; for vegans, reliable fortified foods or supplements
C	90 mg	75 mg	Collagen production, antioxidant functions and improved absorption of non-haem iron	Guava, peppers, citrus, kiwi, broccoli and other fruit and vegetables

NE means niacin equivalents, including the contribution from converting dietary tryptophan. DFE means dietary folate equivalents, accounting for the different absorption of natural food folate and added folic acid. These units should not be treated as interchangeable with every label's raw ingredient amount. [1, 5]

People who smoke need an additional 35 mg of vitamin C daily. The table is not for children, pregnancy or breastfeeding, which have different recommendations. [6]

What is the difference between the two categories?

Feature	Fat-soluble: A, D, E, K	Water-soluble: B vitamins and C
Absorption	Usually absorbed with dietary fat; bile and normal fat digestion are important	Generally absorbed through water-based intestinal processes; some require specialised transport
Storage	Can be stored in the liver and other tissues, although storage differs between vitamins	Often have smaller reserves, but B12 is a major exception
Excess	Some can accumulate and cause harm, especially with high-dose supplements	Some excess is excreted in urine, but large doses can still cause harm
Everyday implication	Include some dietary fat; a completely fat-free approach can interfere with absorption	Maintain a regular supply through a varied diet; do not assume megadoses are harmless

You do not need a large amount of added oil to obtain fat-soluble vitamins. Meals containing nuts, seeds, avocado or other sources of fat can supply dietary fat too.

The water-soluble category does not mean “impossible to overdose.” Excess supplemental B6 can damage nerves; high-dose niacin can cause adverse effects. Biotin supplements can interfere with some laboratory tests, including certain heart and thyroid tests. [5, 7, 8]

Vitamin B12 illustrates why simple rules need exceptions: the body can store substantial reserves, and deficiency may take years to become apparent. Stored reserves are not a reason to ignore a reliable supply. [9]

Which vitamins can we make ourselves?

The answer needs three distinctions: making a vitamin, converting a dietary precursor, and receiving vitamins made by gut microbes.

Vitamin D: production in the skin

Skin can make vitamin D3 when exposed to appropriate UVB radiation. Production varies with age, skin pigmentation, clothing, season, exposure and other factors. Older skin generally produces less. Ordinary window glass blocks UVB, so sitting in sunshine behind a window is not a reliable method. [2]

This does not justify prolonged sunbathing or burning. Food, fortified products and an appropriate supplement can help meet needs without excessive ultraviolet exposure.

Vitamin B3: conversion from tryptophan

The body can make niacin-related compounds from tryptophan, an amino acid supplied by dietary protein. The conversion depends on nutritional status and varies between people. This is why niacin recommendations use niacin equivalents. It is not production without food: we still need the starting materials. [5]

Vitamin A: conversion from plant carotenoids

The body can convert some carotenoids, including beta-carotene, into vitamin A. Carrots, orange sweet potato and leafy greens can therefore contribute without containing preformed retinol. Conversion varies, and not every carotenoid can become vitamin A. [3]

Again, this is conversion of something we eat, not an independent supply.

Vitamin K and some B vitamins: contributions from gut bacteria

Gut microbes can make vitamin K forms and some B vitamins, including biotin and pantothenic acid. The amounts made, available and absorbed are variable or uncertain. We should not subtract a guessed bacterial contribution from our dietary targets or assume fermented food makes every vitamin unnecessary. [4, 8, 10]

Humans do not synthesise vitamin C or vitamin B12. Some microbes can make B12, but microbial production in the gut is not a dependable way to meet human requirements. [6, 9]

For the other vitamins, food remains the dependable basis of supply, with fortification or supplements where needed. Our ability to recycle or convert vitamin forms does not remove the need for nutrition.

Two important points for older plant-based eaters

B12 deserves deliberate attention. Many older adults absorb food-bound B12 less efficiently. NIH recommends that people over 50 obtain most of their B12 through fortified foods or supplements. Ordinary unfortified plant foods, including most fermented foods, are not reliable sources. [9]

The 2.4 µg RDA is not automatically an effective supplement dose. Absorption depends on dose, frequency and individual health, and treatment of deficiency is a separate matter. A clinician can help choose an appropriate regimen. Dr Michael Greger's NutritionFacts.org also discusses reliable B12 sources and supplementation. [11]

Vitamin D becomes a larger dietary target after 70. Its availability in unfortified plant foods is limited, so check actual fortification labels rather than assume every plant milk contains it. [2]

Food first, with supplements for a reason

Vegetables and fruit, legumes, whole grains, nuts and seeds can supply many vitamins, but no single ingredient covers all 13 reliably.

A practical meal might combine lentils or tofu, brown rice, leafy vegetables, orange sweet potato and some seeds, with guava or another fruit. It still needs a separate plan for B12 if you eat vegan, and an assessment of vitamin D intake.

A daily reference amount is not an instruction to take that amount on top of an adequate diet. Supplement labels may list percentages of a general Daily Value that differs from your age- and sex-specific recommendation.

More is not always better. The useful goal is adequacy, not the highest number on a bottle.

Before changing your diet: Consult your doctor or another qualified health practitioner before making dietary changes based on this website, particularly if you have a medical condition, malabsorption or take medication. People taking warfarin need consistent vitamin K intake and professional guidance; they should not simply stop eating greens. Other anticoagulants work differently. Do not use high-dose vitamins to treat unexplained symptoms without assessment. [4]

Sources and further reading

Sources checked on 13 October 2026. The reference system is stated explicitly because international recommendations can differ.