A variety of nutrients have been identified as having direct effects on both humoral and cellular immune responses. Chapters 11 through 16 each present recent information on the role of specific individual nutrients in the immunity response.
Glutamine, the subject of Chapter 11, is a nonessential amino acid that comprises approximately 60 percent of the free amino acid pool in skeletal muscle. It is thought that major illnesses such as injury, burns, and/or other disease states associated with significant inflammatory response initiate an increased glutamine requirement. Studies in bone marrow transplant patients and postoperative patients support the concept that glutamine is a specific growth factor for lymphocytes.
In Chapter 12, the author provides a brief review of vitamin A deficiency as a nutritionally acquired immunodeficiency disorder that primarily affects infants, preschool children, and pregnant and lactating women. Healthy adult men and women are at low risk of deficiency except under conditions of chronic infection or prolonged dietary deprivation.
Recent advances on the immune function response to interventions with vitamins E and/or C are described in Chapter 13. By virtue of their role as antioxidants, these two nutrients have increasingly been applied to clinical situations including aging, cancer, AIDS, asthma, and exercise. Most studies show that vitamin E can improve the immune response during aging, but results have been variable in other situations.
In Chapter 14, the author provides a detailed review of research on the effects of intake of total fat and individual fatty acids on immune response. There are complex interactions between total fat intake, fat composition, ratios of individual fatty acids, duration of feeding, antioxidant nutrient status, and age and health status of the subjects which make it difficult to determine the net effect of fats on immune response. Different indices of immune response respond differently to changes in fat intake. Current recommendations of the American Heart Association of only 30 percent of energy from fat, with 10 percent of energy each from saturated, monounsaturated and polyunsaturated fatty acids will improve immune response in most individuals.
The controversy that has developed in recent years over the relationship between iron nutritional status and susceptibility to infection, mediated by the effects of iron on the host and the pathogen is explored in Chapter 15. The evidence reviewed suggests that iron deficiency provides little nonspecific protection against infections and that iron overload stimulates growth of a very limited number of pathogens, but results in real damage of the immune system. The author believes there are no convincing data that show oral iron supplements for repletion of stores and treatment of iron-deficiency anemia have any adverse impact on response to infectious disease.
A number of studies that have examined the effects of trace elements on immune function are reviewed in Chapter 16. Most of these are important as they demonstrate which immune parameters are sensitive to specific nutrients. However, they are limited in that most do not correlate immune dysfunction with an actual increase in illness. The author's own research with selenium indicates that host nutrition not only affects the host immune response, but also affects the pathogen. Host nutrient deficiency may cause the pathogen to mutate to a more virulent form.