Actively supporting the immune system through nutrition keeps animals healthy for longer. Every day, animals have to protect themselves from pathogens (bacteria, viruses, fungi and parasites) and toxins that can be present everywhere. The life stage of the animal is also important.
The nutritional status has a significant influence on the resistance to pathogens and on how a disease progresses in infected animals. Literature focuses on nutrient deficiencies and the modulation of immune responses. Research has been performed into deficiencies of protein, energy, vitamin A, D, E, C, B-complex vitamins, selenium, iron, zinc and copper. The following relationships were observed, among others:
  • β-carotene and vitamin A stimulate cellular and humoral immune responses
  • Various B vitamins are associated with improved immunity
  • A high concentration of vitamin C stimulates the effectiveness of white blood cells to destroy bacteria
  • Vitamin D controls the activity of T and B lymphocytes, which are important in the adaptive immune system
Vitamin A and β carotene
Sufficient vitamin A in the diet is essential for a good and rapidly functioning immune system. Pay particular attention to this aspect during a young animal's development stage and during infections. Deficiencies are linked to a weakened and delayed immune functioning, such as reduced effectiveness of mucous membranes. Vitamin A is crucial for both the innate and the adaptive immune system. Phagocytes and T- and B-lymphocytes cannot function properly without vitamin A.
In nature, all vitamin A is found in plant-based carotenoids. To convert a carotenoid into vitamin A, this molecule must be split first. This process is highly inefficient, and cats are unable to do this themselves. Adding β carotene to the feed offers a solution, as it stimulates the cellular and humoral immune response and acts as an antioxidant. Studies have also revealed that puppies who are given β carotene also show better innate and adaptive immune responses.
 
B-vitamins
A number of B vitamins are linked to the immune system. With a vitamin B6 deficiency, fewer lymphocytes are produced, which slows the reaction of antibodies.
Niacin (vitamin B3) is important for healthy skin and mucous membranes. With a vitamin B3 deficiency, their effectiveness to act as a natural barrier is reduced and pathogens can invade the body more easily. Dogs can synthesise niacin from tryptophan, whereas cats are unable to do so sufficiently. It is therefore particularly important to provide cats with niacin through the feed.
 
Vitamin B12 is necessary to form proteins and DNA. A deficiency can also damage the immune system. Vitamin B6 and folic acid play a role in protein formation. A too low intake of these vitamins has various effects on the immune system, including reduced activity of NK cells and lower production of cells (including basophils and mastocytes) which carry messages in the immune system via the signalling pathways of histamine.
Finally, a vitamin B1 deficiency can impair the production of cholesterol and fatty acids that support the membrane function. The membrane also forms a barrier against pathogens.
 
Vitamin C
Vitamin C is known for its function in the immune system. A low concentration of vitamin C in the blood is linked to a reduced effect of white blood cells to destroy bacteria. White blood cells require a high concentration of vitamin C, which is also a powerful antioxidant. Vitamin C is also indispensable in the production of collagen, which holds cells together for the protective barrier function. With a vitamin C deficiency, wounds heal more slowly, which may allow (more) pathogens to invade the body.
 
Vitamin E
Vitamin E is the most important fat-soluble vitamin. It acts as an antioxidant in plasma, red blood cells and tissues. It neutralises free radicals and prevents oxidative damage to polyunsaturated fatty acids in cell membranes, among others. Responses of free radicals are associated with responses of the innate immune system.
Insufficient vitamin E in the diet affects the functioning of the immune system. Although deficiencies are rare, extra vitamin E l in addition to the basic needs of the animal can be beneficial. Studies have revealed that this can enhance the functioning of the immune system and reduce the risk of infection, especially in older animals. These effects are explained by the better functioning of T-cells, lymphocyte multiplication, IL-2 production and T-helper cells.
 
Vitamin D
Various components of the immune system (B and T cells, macrophages and dendritic cells) contain vitamin D receptors. Enzymes convert vitamin D3 into the active vitamin D metabolite, which binds to the receptor and can then influence the immune system. A vitamin D deficiency is associated with an increased autoimmune response, as vitamin D also keeps the immune system healthy. In addition, an increased risk of infections has also been observed. Vitamin D activates cytokines from, among others, macrophages, which attack bacteria.