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Vitamins: What Do Vitamins Do?

Friderike Gerlinger

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What do vitamins do? Why do we need them? Humans need vitamins to stay fit: to ensure that our immune system works, to carry out metabolic processes, and to keep bones and muscles healthy.[1] Since, with a few exceptions, we cannot produce vitamins ourselves, we have to consume them in regularly through the food we eat.

The more colorful the better: If you follow a balanced and healthy diet – for example, with your five-a-day, you usually automatically provide yourself with the most important vitamins. However, children and young adults, pregnant and breastfeeding women, older people, and people with certain diseases need to increase their vitamin intake and should pay special attention to their vitamin levels.

Find out everything you need to know about vitamins in our article: What are vitamins, what do vitamins do, and which vitamins are vital for us? We explore how many vitamins we need per day, the difference between water-soluble vitamins and fat-soluble vitamins, and when to supplement – that is, with vitamin supplements.

You can also find more information about specific vitamins in our various Health Portal articles:

What Are Vitamins?

The Latin term vita means life – vitamins are vital substances that our bodies cannot produce themselves, or they cannot produce enough of them. We therefore need to take vitamins regularly with our food.

Vitamins are considered micronutrients. Unlike the macronutrients fat, protein, and carbohydrates, they do not provide the body with energy. Nevertheless, vitamins are indispensable: Our bodies need them for the normal functions, growth, and development of our cells.[2]

Vitamins are produced by plants and microorganisms (such as bacteria) and are mainly found in plant-based foods, such as fruits, vegetables, grains, nuts, and vegetable oils. Animals absorb vitamins through their diet, so meat, fish, eggs, milk, and other animal products can also be a good source of vitamins.[3]

Our body can produce vitamin D itself with the help of sunlight.[4] Nevertheless, more and more people suffer from vitamin D deficiency, especially during the winter months. You can read more about this topic in our Health Portal.

Vitamin D Test by cerascreen

Who Discovered Vitamins?

At the end of the nineteenth and the beginning of the twentieth century, experts from a wide range of scientific fields suspected for the first time that certain diseases were caused by a vitamin deficiency and not, as was often assumed at the time, by infections or toxins.[5]

In 1912, the Polish biochemist Casimir Funk used the term vitamin for the first time in a scientific publication. Funk is considered the co-founder of vitamin treatment because he found out which nutrient components people lacked in certain deficiency diseases (such as scurvy or rickets).[6]

Did you know that the World Health Organization (WHO) reports that women and children from low-income regions of the world are particularly likely to suffer from vitamin deficiencies – this concerns vitamins A, B12, and folic acid, for example. Possible consequences are anemia, blindness, and a higher risk of infections and diseases.[1]

What Vitamins Are There?

There are a total of 13 different vitamins, all of which are essential for life. Experts divide them into two groups – namely, fat-soluble vitamins and water-soluble vitamins:[2]

Water-Soluble Vitamins

Fat-Soluble Vitamins

Vitamin B1

Vitamin A

Vitamin B2

Vitamin D

Vitamin B3 (niacin)

Vitamin E

Vitamin B5 (panthothenic acid)

Vitamin K

Vitamin B6 (pyridoxine)


Folic acid (vitamin B9)


Vitamin B12


Biotin (vitamin H)


Vitamin C


Our bodies can store fat-soluble vitamins in fatty tissue, where they can be accessed, when needed. An overdose of vitamins is therefore theoretically possible – but usually only if you take too high a dose of dietary supplements over a longer period of time.

Important: You should always take vitamin supplements if you have been diagnosed with a vitamin deficiency or if your doctor recommends taking them (for example, due to pregnancy). You can read more about vitamins and diet during pregnancy and breastfeeding in our Health Portal article.

Unlike fat-soluble vitamins, water-soluble vitamins cannot be stored – everything that the body does not process is later excreted in the urine. On the one hand, this means that you cannot overdose on water-soluble vitamins. On the other hand, you have to ensure a regular and sufficient intake of these vitamins, as the body cannot fall back on any reserves.[7]

As far as water-soluble vitamins go, vitamin B12 is an exception because the body can store this vitamin for some time in your muscles and liver.[8] Nevertheless, a regular intake is important. Vegans in particular may suffer from vitamin B12 deficiency and should regularly check their levels.

What Do Vitamins Do?

Vitamins are involved in various important metabolic processes. They keep our bodies healthy and efficient by ensuring the following processes occur, for example:[9, 10]

  • production, growth, and protection of cells
  • bone and blood production
  • functioning of the immune and nervous system
  • wound healing and blood clotting
  • energy production (nutrient utilization)
  • hormone production

What Are Typical Vitamin Deficiency Symptoms?

If your body lacks vitamins, it can no longer perform its tasks and functions as well as it would normally. This can become noticeable in various ways – for example, through the following vitamin deficiency symptoms:[10]

  • tiredness and poor performance
  • susceptibility to infections, wound healing disorders
  • headaches, concentration problems, and dizziness
  • dry, scaly skin
  • anemia and muscle fatigue

Did you know that hair loss can also indicate a vitamin deficiency? Our hair needs biotin, folic acid, vitamin A, vitamin E, and vitamin D to grow healthy and strong.[11] You can read more about the causes of hair loss and what you can do about it in our articles on male hair loss and hair loss in women.

In rare cases, prolonged vitamin deficiency can also lead to specific deficiency symptoms and diseases, such as:

  • bleeding gums (scurvy) due to vitamin C deficiency
  • bone loss, osteoporosis, or rickets due to vitamin D deficiency
  • neural tube defect in infants due to folic acid deficiency during pregnancy
  • night blindness due to vitamin A deficiency

    Which Vitamins Do I Need Every Day?

    How many vitamins you need daily depends on many factors – for example, your age, gender, state of health, and individual requirements (such as pregnancy).

    Did you know that you do not have to reach your daily requirement vitamins every day! You can also take less of a certain vitamin on one day and significantly more on another. Experts say that if you get enough vitamins in a week, you can maintain your health well.[12]

    Preventing Vitamin Deficiency: How to Keep the Vitamins in Your Food!

    With a healthy and balanced diet, you can usually provide yourself with all 13 vitamins quite easily and without thinking. Three handfuls of vegetables and two handfuls of fruit per day are a good rule of thumb.[13]

    However, it is important how you prepare your food. That’s because using the wrong preparation method can mean vitamins are lost! We have therefore summarized some practical cooking tips for you:[14]

    • Keep fresh fruit, vegetables, and herbs in a cool, dry, and dark place and consume them quickly.
    • Natural frozen fruit and vegetables are very good alternatives to fresh produce.
    • Wash fruit and vegetables briefly and thoroughly; do not leave them in water. Cut up produce only after washing.
    • Consume freshly squeezed juices or grated fresh food immediately. Chop herbs just before use.
    • Eat fruit and vegetables raw as often as possible.

    Many vitamins can also be lost during cooking itself. Therefore, you should make note of these handy tips:

    • Steam vegetables and potatoes with little water. Vegetables that are firm contain more nutrients than vegetables that have been cooked until they are soft.
    • Excess cooking liquid can be used to make a sauce.
    • Add fresh herbs just before serving.
    • Do not keep cooked food warm for too long.
    • Cool leftovers quickly and store them in the refrigerator or freezer.

    How Can I Prevent and Treat Vitamin Deficiency with Vitamin Supplements?

    Most people can cover their vitamin needs well through a healthy and varied diet. Vitamin D is an exception, as our body cannot produce enough vitamin D through sunlight during the winter months. We can hardly cover our vitamin requirements through food alone.

    However, ensuring a sufficient supply of vitamins is necessary for certain individuals. Experts recommend vitamin supplements to the following people:[16, 17, 18]

    • Pregnant and breastfeeding women, and women who are trying for children
    • Babies
    • Competitive athletes
    • People with unbalanced diets (such as vegan diets), with food intolerances, or with certain diseases
    • People with high tobacco and/or alcohol consumption
    • Elderly people

    Important: You should only take vitamin supplements after taking a vitamin deficiency test or consulting your doctor. Taking too high a dose of certain vitamins in the long term can be dangerous!

    What Do Vitamins Do – at a Glance

    What Are Vitamins?

    Vitamins are vital substances that our body cannot produce itself or cannot produce sufficiently. We therefore need to take vitamins regularly with our food.

    Which Vitamins Are There and Are They All Important?

    There are 13 different vitamins. Experts divide them into two groups – namely, fat-soluble vitamins (vitamins A, D, E, and K) and water-soluble vitamins (vitamins B1, B2, B3, B5, B6, B12, C, folic acid, and biotin).

    Vitamins are involved in important metabolic processes. They support our body with various tasks, such as the growth and protection of cells, bone and blood formation, the function of the immune and nervous systems, wound healing, and hormone production.

    What Are Common Vitamin Deficiency Symptoms?

    Vitamin deficiency initially leads to generic symptoms such as fatigue and poor performance, susceptibility to infections, wound healing disorders, headaches, concentration problems, and dizziness – as well as dry, flaky skin, and muscle weakness.

    In rare cases, prolonged vitamin deficiency can also lead to specific vitamin deficiency symptoms and diseases, such as bleeding gums, bone loss, or night blindness.

    When Should I Take Vitamin Supplements?

    Most people can get enough of all vitamins through a balanced and healthy diet. The exception is vitamin D, for which experts recommend supplements during the fall and winter months.

    In addition, vitamin supplements are recommended for certain people, such as pregnant and breastfeeding women, infants, people with unbalanced diets, or people with high tobacco or alcohol consumption.


    [1] World Health Organization (WHO), Micronutrients,” available at, accessed on March 3, 2021.

    [2] MedlinePlus, National Institutes of Health, “Vitamins”, available at, accessed on Jan 17, 2022.

    [3] Harvard Health Publishing, Harvard Medical School, "Best source of vitamins? Your plate, not your medicine cabinet" available at, accessed on Jan 17, 2022.

    [4] Deutsche Gesellschaft für Ernährung (DGE) e.V, Vitamin D (Calciferole),, accessed on March 8, 2021.

    [5] Semba R. D. The Discovery of the Vitamins, International Journal for Vitamin and Nutrition Research, vol. 82(5), pp. 310–315, October 2012, doi: 10.1024/0300-9831/a000124.

    [6] Piro A., Tagarelli G., Lagonia P., Tagarelli A., Quattrone A. Casimir Funk: His Discovery of the Vitamins and Their Deficiency Disorders, ANM, vol. 57(2), pp. 85–88, 2010, doi: 10.1159/000319165.

    [7] Harvard Health, Vitamins and Minerals, The Nutrition Source, September 18, 2012, available at, accessed on 4 March 2021.

    [8] Stahl A., Heseker H. Vitamin B12 (Cobalamine): Physiologie, Vorkommen, Analytik, Referenzwerte und Versorgung in Deutschland, Ernährungs Umschau, vol. 10/07, pp. 594–601.

    [9] Reddy P., Jialal I. Biochemistry, Fat Soluble Vitamins, in StatPearls, Treasure Island (FL): StatPearls Publishing, 2021.

    [10] Lykstad J., Sharma, S. Biochemistry, Water Soluble Vitamins, in StatPearls, Treasure Island (FL): StatPearls Publishing, 2021.

    [11] Guo E. L., Katta R. Diet and hair loss: effects of nutrient deficiency and supplement use, Dermatol Pract Concept, vol. 7(1), pp. 1–10, January 2017, doi: 10.5826/dpc.0701a01.

    [12] Bundesministerium für Soziales, Gesundheit, Pflege und Konsumentenschutz, Vitamine - Deckung des Tagesbedarfs, Gesundheitsportal, July 15, 2020, available at, accessed on March 11, 2021.

    [13] Deutsche Gesellschaft für Ernährung e. V., 10 Regeln der DGE“, Vollwertig essen und trinken nach den 10 Regeln der DGE, available at, accessed on March 9, 2021.

    [14] Schülein A., Schaechtele, J. Lebensmittel garen, Bundeszentrums für Ernährung (BZfE), March 18, 2020, available at, accessed on March 11, 2021.

    [15] National Health Service (NHS), Do I need vitamin supplements?“,, June 26, 2018, available at, accessed on March 11, 2021.

    [16] A. Jungert, K. Quack Lötscher, und S. Rohrmann, Vitaminsubstitution im nichtkindlichen Bereich“, Deutsches Ärzteblatt, January 6, 2020, available at, accessed on March 11, 2021.

    [17] Deutsche Gesellschaft für Ernährung e. V., Bunte Pillen für’s gute Gewissen – Was bringen Nahrungsergänzungsmittel?“ December 4, 2004, available at, accessed on March 11, 2021.

    [18] A. Bechthold, V. Albrecht, E. Leschik-Bonnet, und H. Heseker, Beurteilung der Vitaminversorgung in Deutschland. Teil 2: Kritische Vitamine und Vitaminzufuhr in besonderen Lebenssituationen, Ernährungs Umschau, July 2012, available at, accessed: March 11, 2021.

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