Increased Micronutrient Requirements during Physiologically Demanding Situations: Review of the Current Evidence

A Review of Micronutrients and the Immune System–Working in Harmony to Reduce the Risk of Infection

“…Activated macrophages can synthesize calcitriol from circulating calcidiol, and calcitriol increases the proliferation and differentiation of monocytes to macrophages [8,27,87]. Calcitriol also promotes the movement and phagocytic ability of macrophages [27], and increases their oxidative burst potential [24][25][26]. Vitamin C stimulates the production and function of leukocytes, particularly the movement of neutrophils and monocytes, and is readily mobilized during infection [24].…”

“…Calcitriol also promotes the movement and phagocytic ability of macrophages [27], and increases their oxidative burst potential [24][25][26]. Vitamin C stimulates the production and function of leukocytes, particularly the movement of neutrophils and monocytes, and is readily mobilized during infection [24]. In a recent study, neutrophils isolated from healthy individuals were preloaded with dehydroascorbic acid to increase intracellular vitamin C levels [28].…”

“…Vitamin A helps to regulate the production of IL-2 and the proinflammatory TNF-α, which activates the microbial action of macrophages [8]. Administration of vitamin D reduces the expression of pro-inflammatory cytokines and increases the expression of anti-inflammatory cytokines by macrophages via upregulation of MAPK phosphatase-1 and suppression of p38 activation [24,[46][47][48]. Vitamin E decreases the production of prostaglandin E2 (which has immunosuppressive activity) [8], and vitamin C modulates cytokine production and decreases histamine levels [21].…”

“…Vitamin D is an immunosuppressive hormone [62]; calcitriol inhibits the proliferation and differentiation of T and B cells [7,27], but production of calcitriol by DCs "programs" T-cell homing to the epidermis, which is essential for long-term immune surveillance and maintenance of the barrier integrity [61,96]. In contrast, vitamins C and B12 facilitate the production of T cells, particularly cytotoxic T cells [24,35]. Zinc is also essential for the development, differentiation, and activation of T lymphocytes [8,49], while iron, copper, and selenium are important in their differentiation and proliferation [2,7,35].…”

“…Even in industrialized countries, multiple micronutrient deficiencies are widespread and may exacerbate the risk of infection [113,114]. The severity of any adverse health effects largely depend on the extent and duration of micronutrient deficiency [24]. There is much less information on health effects when micronutrient status is suboptimal (rather than clinically deficient), including what levels can be defined as "suboptimal" (particularly in different populations in whom "optimal" levels may vary, i.e., the levels that would provide optimized function or protection against health risk) [24], and how to define the levels of a micronutrient that are optimal in terms of immune function.…”