Immune Compromise Due to Metabolic Disorders: Malnutrition, Obesity, Stress, and Inborn Errors of Metabolism

Secondary or acquired immune deficiencies are often missed by the clinician since they occur in circumstances that can be easily overlooked, or not appreciated or differentiated from the primary underlying disease. Primary malnutrition from an inadequate intake of selected micronutrients or vitamins leading to increased susceptibility to infections and co-morbid conditions can be clinically significant. These nutrient deficiencies occur most commonly in Third World countries, but, surprisingly, can also occur in industrialized nations because of lack of access to care or poor nutrition for socio-economic reasons. Metabolic deviations such as diabetes, obesity, and inborn errors of metabolism can lead to changes in immune function and increased susceptibility to infection. In fact, the increased susceptibility to infections and the developing immune deficiency can be a "window" into the primary causes leading to these secondary immune deficiencies. In a somewhat related subject of secondary immune deficiency, too much of a good thing can also lead to immune deviations. Thus, over-exercise or changes in mental states, such as stress, can lead to immune deficiencies. This topic of acquired or secondary immune deficiency is often neglected, except of course for HIV infection. Although the topic is very broad and often complex, this chapter will provide "brush strokes" for gaining a better appreciation of the secondary immune deficiency disorders.