Many studies have attempted to boost immunity through a variety of interventions. Most of the studies that have looked at the addition of vitamin and antioxidant supplements to the diet have not proven that these supplements improve immunity. One Canadian study, however, did show that older adults who took multivitamin tablets did have stronger immunity and fewer infections that those who were given placebo. It is also clear that malnutrition contributes to the depression of the immune response. Thus, many scientists recommend that the best diet, for a variety of reasons, perhaps including maintaining immune response, is one that is weighted toward fruits and vegetables, which contain natural antioxidants.

Other lifestyle changes can improve immune function, as well. For example, it is never too late to quit smoking. Smoking raises the risk of a variety of infectious diseases, such as pneumonia and bronchitis, as well as a whole raft of age-related diseases and conditions including heart disease and cancer.