What is the best multivitamin for men or immune system?

Not one choice but: The only vitamin which appears to have the greatest potential in regulating the immune system is vitamin d3. The lower normal limit in blood vitamin d3 level is targeted towards the bone since a higher level is likely needed for immune function. Other supplements such as zinc, beta carotene, Folic Acid etc have been touted as immune boosters but the evidence is very weak.