...as scientists discover more about how the immune system works, they are finding evidence that it is the complex interaction of nutrients in real food that helps the body build its defenses against disease and infection. They even warn that large doses of some supplements such as selenium, zinc, vitamin A, vitamin B6 and vitamin E may even harm and suppress the immune response..
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http://newsofthenorth.net/article/Community/HealthWellness/Healthy_food_is_the_best_way_to_boost_the_immune_system/27922