"There is an emergent interest in understanding how the ‘Western diet’ affects immunity. Many people across the globe have adopted this diet, and epidemiological studies have revealed that it correlates with a high incidence of chronic inflammatory disorders, including diabetes, multiple sclerosis and asthma. Nevertheless, because the Western diet includes a large proportion of red meat, sugars, fats and refined carbohydrates and relatively small amounts of vegetables, fruits and fish, it is likely that the causative component of its associated pathologies is not a single entity but a complex array of unbalanced abundance of micronutrients in the diet. However, epidemiological studies have highlighted roles for specific micronutrients in immunity. For example, mounting evidence correlates vitamin A deficiency, which is still highly prevalent among children and pregnant women in several African and Asian countries with a high risk of intestinal and respiratory infections. These observations were substantiated by experimental data as early as 1925, when rats on a diet deficient in vitamin A were found to develop thymic atrophy. It is now understood that different processes require different amounts of micronutrients, with the immune system generally the largest consumer. In view of this, the World Health Organization established a vitamin A–supplementation program, which had a positive effect on morbidity and mortality rates of infectious diseases in deprived children. Interestingly, low vitamin A levels are also associated with reduced efficacy of vaccination protocols, but the benefits of vitamin A supplementation during vaccination are still a matter of controversy."