Thirteen substances the body needs but cannot produce itself – at least not in sufficient quantity. That is the entire definition of a vitamin. What is remarkable is how long science took to arrive at this simple idea, and how often it has gone astray since then by isolating individual vitamins from food and administering them at high doses.
Why there are exactly thirteen vitamins, and what actually connects them
Chemically, vitamins have almost nothing in common. They belong to entirely different classes of compounds, look nothing alike and perform completely different tasks in metabolism. What makes them a group is a purely negative criterion: the human organism cannot produce them at all, or cannot produce them in sufficient quantity, and therefore has to obtain them from food. That is also why the list is not arbitrarily long – thirteen compounds or groups of compounds meet this criterion in humans.
The path to this insight runs right across Europe. In 1747, the Scottish naval surgeon James Lind conducted one of the first controlled therapeutic experiments in medical history aboard the «Salisbury» and observed that sailors given citrus fruit recovered from scurvy. Some 150 years later, the Dutch physician Christiaan Eijkman showed in Java that chickens fed polished rice developed a condition resembling beriberi – and that returning the removed rice husks reversed it. Eijkman received the Nobel Prize for this work in 1929, together with Frederick Gowland Hopkins.
The name itself was coined by the Polish biochemist Kazimierz («Casimir») Funk, who studied biology and chemistry in Geneva and completed his doctorate at the University of Bern in 1904. He suspected that the factors being sought were vital amines and proposed the term «vitamine» in 1912. Chemically he was wrong – most of these substances are not amines. The name stuck all the same; only the final «e» was dropped later in English.
Fat-soluble or water-soluble – the distinction that governs storage and risk
The most practically important classification of vitamins is not functional but physical. Four vitamins are fat-soluble: they are absorbed together with dietary fat, stored in the liver and adipose tissue, and barely excreted in urine. The remaining nine are water-soluble; here, excess largely leaves the body via the kidneys. This explains why a persistently excessive intake matters more with fat-soluble vitamins than with water-soluble ones – vitamin B12 being the well-known exception, as it is also stored in the liver.
| Vitamin | Involved in (physiology) | Important food sources |
|---|---|---|
| Fat-soluble | ||
| A (retinol, provitamin A carotenoids) | Vision, cell division and differentiation, immune function | Liver, egg yolk, butter; carotenoids in carrots, squash, dark green vegetables |
| D (calciferols) | Calcium and phosphate metabolism, bone mineralisation | Formed in the skin under UV-B; additionally oily fish, egg yolk, mushrooms |
| E (tocopherols, tocotrienols) | Protection of membrane lipids against oxidation | Vegetable oils, nuts, seeds, wheat germ |
| K (phylloquinone, menaquinones) | Blood coagulation, activation of bone proteins | Green leafy vegetables, cabbage, fermented foods |
| Water-soluble | ||
| B1 (thiamine) | Carbohydrate metabolism, function of nerves and heart muscle | Wholegrain products, pulses, pork |
| B2 (riboflavin) | Energy metabolism, regeneration of other redox systems | Dairy products, eggs, wholegrains, almonds |
| B3 (niacin) | Energy metabolism as a component of central coenzymes | Meat, fish, wholegrains, peanuts |
| B5 (pantothenic acid) | Component of coenzyme A, fat and carbohydrate metabolism | Widely distributed; particularly pulses, nuts, mushrooms, offal |
| B6 (pyridoxine and related forms) | Amino acid and protein metabolism, formation of neurotransmitters | Fish, poultry, potatoes, bananas, wholegrains |
| B7 (biotin) | Fatty acid synthesis, gluconeogenesis | Egg yolk, nuts, oats, liver |
| B9 (folate; folic acid in synthetic form) | Cell division, blood formation, transfer of one-carbon units | Green leafy vegetables, pulses, wholegrains, beetroot |
| B12 (cobalamins) | Blood formation, nerve function, folate metabolism | Practically only foods of animal origin |
| C (ascorbic acid) | Collagen formation, absorption of iron from plant sources, protection against oxidation | Vegetables and fruit, particularly brassicas, berries, citrus fruit |
What the national nutrition survey menuCH shows about supply in Switzerland
Thanks to menuCH, representative consumption data have been available for Switzerland for the first time. In this cross-sectional study, a total of 2,085 people aged 18 to 75 were each interviewed twice between January 2014 and February 2015 about what they had consumed in the preceding 24 hours. The micronutrient intake calculated from these data was analysed in 2021 in the Swiss Nutrition Bulletin published by the Federal Food Safety and Veterinary Office and compared against the D-A-CH reference values.
The result is more nuanced than the widespread talk of «vitamin deficiency» would suggest. For thiamine, riboflavin, niacin and vitamins A, B6, B12, C and E, intake appeared adequate for the majority of the adult population. Three vitamins, by contrast, fell below the recommendation across all age and sex groups:
- Folate: intake reached 80 to 88 per cent of the D-A-CH reference value depending on the group; only men aged 35 to 49 reached 92 per cent.
- Pantothenic acid: no age group reached the estimated value of 6 mg per day; among women, values ranged from 3.9 to 4.3 mg.
- Vitamin D: calculated intake from food ranged from 2.5 to 3.9 µg per day – a fraction of the 15 µg recommended by the federal office.
Regional differences also became visible. Folate intake was lower in Ticino than in the rest of Switzerland, while men in the French-speaking region and in Ticino reached more than double the reference value for vitamin B12. German-speaking Swiss women were the only group not to reach the B12 recommendation – a finding the authors connect to that group's lower meat consumption.
Three qualifications belong with these figures, and the report names them itself. First, food supplements were recorded only qualitatively and were not included in the calculation; actual intake is therefore likely to be higher, particularly as an estimated 14 to 30 per cent of the population in Switzerland use such products. Second, 24-hour recalls rely on self-reporting and are prone to misreporting. Third, the comparison was made against reference values designed to cover the requirements of around 98 per cent of healthy people – an intake below that therefore does not automatically indicate an individual deficiency. A comparison against the lower estimated average requirements would produce a different picture.
Why vitamin D is a special case in Switzerland
With vitamin D, diet is in any case a side issue. What matters is the body's own synthesis in the skin under UV-B radiation – and that depends on latitude. At Switzerland's latitude, solar radiation is insufficient for this during the winter months. The Federal Food Safety and Veterinary Office assumes that around 60 per cent of the population have an inadequate vitamin D supply in winter, and states the following reference values:
| Population group | Recommended daily intake |
|---|---|
| Infants in the first year of life | 10 µg (400 IU) |
| Children in their second and third year | 15 µg (600 IU) |
| People aged 3 to 60 | 15 µg (600 IU) |
| Pregnant and breastfeeding women | 15 µg (600 IU) |
| People aged 60 and over | 20 µg (800 IU) |
At the same time, vitamin D is the vitamin currently subject to the fiercest debate. A systematic review with meta-analysis published in 2018 in «The Lancet Diabetes & Endocrinology» pooled 81 randomised controlled trials and concluded that vitamin D supplementation in adults prevented neither fractures nor falls, and did not change bone density to a clinically meaningful degree – irrespective of dose.
This work did not go unchallenged. The subsequent professional correspondence objected that studies using combined vitamin D and calcium supplementation had been excluded, that very high bolus doses had been included, and that the majority of participants were already adequately supplied at baseline. The Swiss Federal Commission for Nutrition maintained the Swiss recommendation in its statement, pointing to the documented prevalence of low blood values in Switzerland, particularly among older people. Anyone following this debate sees a pattern that runs through the whole of vitamin research: whether supplementation achieves anything depends less on the nutrient than on how well supplied the people studied were beforehand.
What happens when individual vitamins are isolated and given at high doses
The observation that people eating plenty of fruit and vegetables develop certain diseases less often led in the 1980s to an obvious hypothesis: isolate the vitamins responsible and give them at high doses. The major tests of this hypothesis are among the most instructive chapters in nutrition research.
In the Finnish ATBC study – a randomised, double-blind, placebo-controlled trial – 29,133 male smokers aged 50 to 69 received 20 mg beta-carotene, 50 mg alpha-tocopherol, both, or placebo daily over a median of just over six years. Lung cancer incidence did not fall; in the beta-carotene group it was higher than in the comparison group. The American CARET study in smokers and asbestos-exposed workers was stopped early in 1996 for the same reason.
A Cochrane review from 2012 pooled 78 randomised trials with 296,707 participants and found no evidence that antioxidant supplements reduce mortality; for beta-carotene and vitamin E, trials at low risk of bias even showed slightly increased figures. This analysis, too, is professionally contested – criticism has focused among other things on trial selection and on transferability to low-dose preparations. What is undisputed is the core message in its more moderate form: an isolated vitamin at a high dose does not behave like the same vitamin in a carrot.
Against this stands an equally clear counter-example. The MRC Vitamin Study, published in «The Lancet» in 1991, randomised 1,817 women with a previous pregnancy affected by a neural tube defect to folic acid, other vitamins, both, or neither. Six of 27 neural tube defects occurred in the folic acid groups and 21 in the others – a protective effect of 72 per cent (relative risk 0.28; 95 per cent confidence interval 0.12 to 0.71). The other vitamins tested showed no corresponding effect. Important for interpretation: this was a clearly defined high-risk group, not the general population.
For vitamin C the balance is more modest, and frequently overstated. The 2013 Cochrane review found, across 31 comparisons, no reduction in the frequency of colds in the general population; with regular intake, average cold duration was around 8 per cent shorter in adults (95 per cent confidence interval 3 to 12 per cent) and around 14 per cent shorter in children. For intake begun only after symptom onset, no consistent effect could be shown.
Where targeted supplementation is professionally undisputed
A workable rule of thumb can be derived from this mixed picture: the more clearly a group can be defined in which intake is structurally low, the better the evidence for targeted supplementation. In Switzerland this essentially concerns three constellations.
Vitamin D during the winter months – here the federal authorities follow the logic that skin synthesis fails seasonally and that diet can hardly close this gap. Intake is recommended particularly for infants, pregnant and breastfeeding women, and people aged 60 and over.
Folic acid before and in early pregnancy – the recommendation to begin before conception follows directly from the evidence described above and from the fact that neural tube closure takes place in the first weeks of pregnancy, often before the pregnancy is even known.
Vitamin B12 on a purely plant-based diet – B12 occurs in relevant amounts practically only in foods of animal origin. A 2013 review evaluated 18 studies that determined status via methylmalonic acid or holotranscobalamin and found widely varying, in part high proportions with reduced values depending on the group; among people living vegan they were consistently higher than among vegetarians. The Swiss Federal Commission for Nutrition addressed this accordingly in its report on vegan diets.
Safety and use: what to bear in mind with vitamins
Fat-soluble vitamins are more sensitive to sustained excess. Because they are stored and barely excreted, an intake that is markedly too high over a long period can accumulate. In 2024, the European Food Safety Authority reviewed the tolerable upper intake level for preformed vitamin A and retained it at 3,000 µg retinol equivalent per day for adults; the decisive factor was its teratogenic potential. Provitamin A carotenoids from plant foods are not covered by this, as conversion in the body is regulated according to need.
Pregnancy and breastfeeding. Liver and liver products are avoided during pregnancy because of their high retinol content. Preparations containing preformed vitamin A belong in medical consultation during this period. For folic acid, vitamin D and iodine, by contrast, separate official recommendations exist.
Children. Reference values for children are not simply scaled-down adult values, and safety margins are narrower. Vitamin preparations for children belong in paediatric assessment.
Interactions. Vitamin K acts on blood coagulation and is relevant during anticoagulant therapy with vitamin K antagonists. Various medicines also affect vitamin status. Anyone taking medication regularly should clarify supplementation with a doctor.
Accumulation from several sources. A 2022 survey by the Federal Food Safety and Veterinary Office among 1,282 adults in Switzerland showed that exceedances of tolerable upper levels are rare when supplements are the only source – but that they can occur when several products are combined. Anyone using several preparations in parallel is well advised to add up the amounts.
Conclusion: what has been shown and what remains open
It has been shown that all thirteen vitamins are indispensable for metabolism and that a pronounced deficiency causes clearly delineated clinical pictures – nothing has changed there since Lind and Eijkman. It has equally been shown that intake in Switzerland falls below the reference values for folate, pantothenic acid and above all vitamin D, with marked differences by sex, age and language region.
Open – or in some cases answered rather in the negative – is the separate question of whether additional intake produces measurable benefit in people who are already well supplied. The large intervention trials have not confirmed this hope for high-dose single vitamins, and in part have suggested the opposite. The benefit is best documented where a structural gap exists: vitamin D in winter, folic acid around conception, vitamin B12 on a purely plant-based diet. For all other vitamins the evidence remains most solid for what sounds least spectacular – vegetables, fruit, wholegrains, pulses, nuts and oils in sensible proportions. In the menuCH analysis, 63 per cent of vitamin C intake and around 40 per cent of folate intake came from vegetables and fruit, and around half of vitamin E intake from oils, fats and nuts.
This article is for general information only and does not replace medical advice, diagnosis or treatment. Food supplements are not a substitute for a balanced and varied diet and a healthy lifestyle. If you have health complaints, during pregnancy and breastfeeding, for children, and if you are taking medication, please consult a doctor.
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