Exposure of laboratory animals to small air ions: a systematic review of biological and behavioral studies

Abstract

BackgroundAir ions are molecules of air that have become ionized—that is, they have either lost or gained an electrical charge. Past speculation has suggested that exposure to positive air ions may be harmful to one’s health, while exposure to negative air ions may be associated with beneficial health effects. Air ions arise from natural sources as well as direct-current transmission lines and commercial ionizers. Several recent clinical studies have suggested therapeutic effects of air ions on various types of depression at exposure levels 10- to 1000-fold higher than most previous human studies. The aim of this study was to assess the evidence from studies of laboratory animals for beneficial or adverse effects of air ions on health.MethodsSixty-two studies (1935–2015) in nine topics areas were evaluated for quality and potential systematic bias by ARRIVE guidelines. Standardized mean differences or proportional differences between exposed and control groups were computed for 44 studies to quantitatively assess the strength of the evidence for exposure-related effects.ResultsMany of the studies were conducted before 1990 and exhibited various reporting and methodological deficiencies, including small sample size, failure to control for the influence of potential confounding variables, lack of randomized assignment to treatment groups and blinded analyses, and statistical errors relating to treating group-exposed animals as individuals. The highest quality studies consistently reported no effects of exposure on any of the endpoints examined. There were no evident dose–response relationships within or across studies.ConclusionsExperimental studies of laboratory animals exposed to positive and negative air ions for minutes to years over a five-log unit range of intensities did not suggest any consistent or reliable effects on measures of behavior, learning and memory, neurotransmitters, tracheal function, respiratory infection, cardiovascular function, reproduction and growth, carcinogenesis, or other health endpoints. These data do not provide evidence of adverse or beneficial effects of air ion exposure on health, and did not suggest any biological mechanism of interaction, except perhaps for mechanosensory stimulation of body surfaces by static electric fields at high air ion concentrations.Electronic supplementary materialThe online version of this article (10.1186/s12938-018-0499-z) contains supplementary material, which is available to authorized users.

Negative Air Ions and Their Effects on Human Health and Air Quality Improvement

“…However, other studies showed that the lifetime of NAIs in clean air is around 100 s ([ 34 ] and references therein). In fact, several other factors including the concentrations of NAIs and aerosols, and the intensity of electric fields may affect lifetimes of NAIs [ 35 ]. This may explain why different lifetimes were reported by several different references as mentioned above.…”

“…Thus, some of the biological effects of NAIs were related to the reduction of serotonin. However, others reported no significant effect of NAIs on the concentration or turnover of serotonin in rats under their exposure conditions [ 35 , 79 ]. Bailey et al (2018) carried out a comprehensive review on the effects of air ions on serotonin and other neurotransmitters and their analysis indicated some modest or strong evidence to support no effect hypothesis [ 35 ].…”

“…There are many references to report the possible biological effects [ 24 , 32 , 33 , 35 , 38 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 , 102 , 103 , 104 , 105 , 106 , 107 , 108 , 109 , 110 , 111 , 112 , 113 , 114 , 115 , 116 , 117 , 118 , 119 , 120 , 121 , 122 , 123 , 124 ]. And some of them were listed in Table S2 .…”

“…The effects of NAIs on the cardiovascular system included improving erythrocyte deformability and aerobic metabolism [ 24 ] as well as decreasing blood pressure [ 32 , 77 , 81 , 82 ]. However, no effect was also reported on blood pressure [ 83 ] or heart rate [ 84 , 85 ] and related data on cardiovascular function studies were not quantitatively evaluated [ 35 ]. On mental health, exposure to NAIs showed highly significant increase in performance of all tested tasks (mirror drawing, rotary pursuit, visual reaction time, and auditory) [ 86 ], alleviating symptoms of seasonal affective disorder (SAD) [ 87 ].…”

“…On the contrary, no effect of NAIs on mental health was reported in other studies [ 89 , 90 ]. Comprehensive analysis on literatures showed no conclusive results on the potential therapeutic effects of NAIs on depression [ 35 ]. As for the effect of NAIs on respiratory function, exposure to negative or positive air ions does not appear to play an appreciable role in respiratory function [ 91 ].…”