Nutrition and immunity: General principles

Abstract Text:

The development, maintenance and response of the immune system are influenced by nutrition. For most nutrients the most important nutritional strategy for optimizing immunity is meeting the established requirements for maximizing growth, reproduction and feed efficiency and avoidance of traditional signs of deficiency. Severe deficiencies of required nutrients typically impair host immunity and resistance to disease, but such deficiencies should be rare in modern animal production. More relevant are marginally deficient and surfeit levels of nutrients.  In the case of several essential nutrients, leukocytes, especially T lymphocytes, are very sensitive to marginal deficiencies, while for many other nutrients the immune system is largely unaffected by marginal deficiencies. This difference in sensitivity is due the types and amounts of nutrient transporters expressed on each cell type.  Nutrients also support the anabolic processes of pathogens and increase their pathogenicity; though this troublesome effect is likely limited to a small subset of nutrients. Iron in particularly can increase the pathogenicity of some pathogens when provided in excess. Several essential and non-essential nutrients have regulatory effects on leukocytes. Required nutrients with indisputable immunoregulatory actions in rodents and livestock include the long-chain polyunsaturated fatty acids (PUFA) and vitamins A, D, and E. Many nutrients that are not normally considered as being dietary essential also modulate immunity, including carotenoids, vitamin C, and phytonutrients (e.g. capsicum, genistein, curcumin, essential oils, conjugated linoleic acids). In general those nutrients that are not structural components or co-factors for enzymes are most likely to be immunomodulatory. Unlike increases in nutrients from deficient to sufficient levels, where many indices of immunocompetence go from impairment to normal function, supplementation of immunomodulatory nutrients causes some components of immunity to be elevated and others to be diminished; in other words the type and intensities of responses have been changed (i.e. immunomodulated). In situations where a single infectious disease dominates the production losses and where it is clearly known what type of immune response optimally protects against that disease, supplementation of a nutrient that modulates the immune system towards that optimal response is indicated. Thus, the value of an immunomodulatory nutrient to “improved” immunity is context dependent and depends on the types of disease challenges in a herd. In summary, nutritional impacts on immunity are complex and their understanding and applications requires a “first principles” approach.

Keywords: disease, immunity, deficiency