Negative ions accelerate the oxidative degradation of serotonin whereas positive ions have the opposite action and inactivate the enzymes which break down serotonin. The regulation of serotonin levels is calming and increases defenses against infection, as proven with influenza flu.
Negative ions produce an increase in hemoglobin/oxygen affinity so that the partial oxygen pressure in the blood rises but the partial dioxide pressure decreases. This results in reduced respiratory rate and enhances the metabolism of water-soluble vitamins. In addition, negative ions produce an increase in pH making body fluids more alkaline.
Source: Raum und Zeit (Space and Time), Vol 1, No 5, 1989/90, page 85