Immune system of athletes (Part four)

Vitamins are vital organic substances, which are needed for enzymatic and regulatory tasks in many processes in our body. In addition, they are responsible for maintaining the health of the organs and the functioning of the immune system. They also help in some metabolic processes. It is important to get these micronutrients through food in order to have a functional, healthy organism. The most important vitamins with immune-relevant effects are explained below, including vitamins A, D, B6 and C.

Vitamin A:

There are several natural forms of vitamin A. Vitamin A from animal foods (milk, meat, eggs) is called retinol. During absorption, retinol is split off from fat and is bound in the bloodstream by means of a transport protein. This transport protein is zinc-dependent. Disorders of the zinc metabolism result in vitamin A not being synthesised sufficiently. The plant precursor of vitamin A is called carotenoids, which can be converted into vitamin A by the body. If there is an excess of vitamin A in the body, the carotenoids can act as antioxidants. 

The functions of vitamin A are wide-ranging. They act synergistically with iron in building red blood cells. In addition, vitamin A participates in the synthesis of proteins and in fat metabolism in the liver. 

Vitamin A also has an important role in immunity. It increases resistance to infections by being responsible for the integrity of the skin and mucous membranes.

Vitamin A is also involved in the formation of bones and is needed for growth and the healing of bone fractures.

Recommended daily intake

  • Men: 3300 IU*
  • Women: 2600 IU

Occurrence in 100 g:

  • Beef liver 30000 IU
  • Eggs (1 pc.) 400 IU
  • Cheddar cheese (30 g) 340 IU
  • Carrots (1 large) 9200 IU
  • Spinach 2250 IU

Vitamin D:

Vitamin D is the only vitamin where the biologically active form is a hormone. Our skin synthesises vitamin D from cholesterol under the influence of sunlight. Vitamin D is essential for normal bone formation and stimulates muscle cell growth. Furthermore, vitamin D supports the activation and reaction of white blood cells during infections.

In certain regions or seasons, where the body cannot produce vitamin D by means of sunlight, supplementation in the form of a vitamin D supplement is useful.

Recommended daily intake

  • Men: 5 - 10 µg
  • Women: 5 - 10 µg

Occurrence in 100 g:

  • Salmon 16 µg
  • Tuna 5 µg
  • Chicken egg (1 large) 1 µg
  • Calf's liver 1 µg

Vitamin B6:

Vitamin B6 contributes to the integrity of the immune system and is essential for the formation of haemoglobin and for the transport of oxygen by red blood cells. 

In addition, vitamin B6 can maintain normal blood sugar levels by converting protein and carbohydrate stores into glucose. Vitamin B6 also plays an important role in fat metabolism. It synthesises fats that form the myelin sheath to protect the nerve cord.

Recommended daily intake

  • Men: 1.4 - 1.6 mg
  • Women: 1.2 mg 

Occurrence in 100 g:

  • Potatoes (1 medium size) 0.7 mg
  • Banana (1 medium size) 0.6 mg 
  • Lentils 0.6 mg
  • Spinach 0.2 mg

Vitamin C:

Vitamin C is an important water-soluble antioxidant. It is found in every cell of our body and protects them from oxidation with free radicals. Furthermore, cholesterol degradation depends on vitamin C. In addition, it is responsible for the absorption of iron from food.

Recommended daily intake

  • Men: 100 mg
  • Women: 100 mg

Occurrence in 100 g:

  • Acerola cherry 1500 - 2000 mg 
  • Papaya 195 mg
  • Broccoli 115 mg
  • Kiwi 80 mg
  • Orange 70 mg


* 1 µg = 40 International Units (IU); 1 IU = 0.025 µg.


Burgerstein, U. P., Schurgast, H. & Zimmermann, M. (2012). Handbuch Nährstoffe. 12. Aufl. Verlag: Trias.1.

Deutsche Gesellschaft für Ernährung, Österreichische Gesellschaft für Ernährung, Schweizerische Gesellschaft für Ernährungsforschung, Schweizerische Vereinigung für Ernährung (Hrsg.): Referenzwerte für die Nährstoffzufuhr. Bonn, 2. Auflage, 6. aktualisierte Ausgabe (2020)

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