Do Vitamins A, E and Zinc Affect Immunity in Well-Nourished Seniors?
Three nutrients that are needed for the immune system are vitamins A, E and zinc. Deficient individuals have a compromised immune system. The elderly appear to be at increased risk of vitamin deficiencies and also seasonal influenza, which is why Sundaram and co-workers investigated the relationship.
Zinc deficiency impairs cell-mediated immunity, which involves parts of the innate immune system (Prasad). As vitamin A is required for the proper development of mucous membranes, it plays a key role in maintaining the body’s barriers against infection. Dr Ross also explains about its role in immunity via effects on T-cells. Wu and Meydani discuss the effect of vitamin E on age-related immune system deficits, which relate to impaired production of T-cell, cytokines and other parts of the innate and adaptive immune response.
The authors in the current study measured levels of zinc, vitamin A and vitamin E in adults aged over 65 who were living independently, both before and after administration of the seasonal influenza vaccine. The authors measured change in sero-conversion to the strains used in the vaccine and related this to levels of the micronutrients. Unfortunately for the study, no subjects were found to be deficient in vitamins A and E. The serum retinol test used in the study does not differentiate between “good” and “better” status; it is only used to diagnose frank deficiency. 20% of subjects were found to be deficient in zinc. Outside of deficiency, the serum zinc levels as were used in this article are poorly correlated with zinc status (Gibson and co-workers).
It is perhaps not surprising that there was no relationship between levels of zinc, vitamin A and vitamin E in response to influenza vaccination. Firstly, the micronutrients studied appear to have a stronger effect on the innate immune system, and not the antibody response that is measured by the Hemaglutination Inhibition Assay that was used to quantify immune response. Secondly, there were no people deficient in vitamin A or E, and the tests used for vitamins A and zinc correlate poorly with status in well-nourished populations. Nutrient deficiency was not used as a variable in the analyses with zinc.
Nutrient intakes, such as with many other things in life, follow an inverse-U shaped trend. It is important to avoid deficiency. It is also important to avoid toxicity. More is not better; rather, we need to get the right amount, not too little and not too much. Although the study did not find a relationship between zinc, vitamin A and vitamin E with antibody response to influenza vaccination, such a finding would be extremely unlikely given so few people were deficient, and the effects of these nutrients on the immune system do not relate directly to antibody production. Clearly, nutrition is important to avoid deficiency and associated illness in aging populations (see position statement from the American Dietetic Association). Vitamins A, E and zinc are essential for normal immune function. Once levels are adequate, however, there is unlikely to be a clear improvement in measures of immunity when levels increase, as was found in this study.
Maria E. Sundaram, Simin Nikbin Meydani, Mary Vandermause, David K. Shay, Laura A. Coleman. Vitamin E, vitamin A, and zinc status are not related to serologic response to influenza vaccine in older adults: an observational prospective cohort study. Nutrition Research, Available online 18 December 2013. http://dx.doi.org/10.1016/j.nutres.2013.12.004
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