http://www.ncbi.nlm.nih.gov/pubmed/19263912 Vitamin C and immune function. [Vitamin C and immune function]. http://www.ncbi.nlm.nih.gov/pubmed/19263912 http://www.ncbi.nlm.nih.gov/pubmed/19263912 Medizinische Monatsschrift fur Pharmazeuten strengthen the immune system http://www.ncbi.nlm.nih.gov/pubmed/19263912 strengthen the immune system