Air ions and mood outcomes: a review and meta-analysis

Abstract

Background: Psychological effects of air ions have been reported for more than 80 years in the media and scientific literature. This study summarizes a qualitative literature review and quantitative meta-analysis, where applicable, that examines the potential effects of exposure to negative and positive air ions on psychological measures of mood and emotional state.

Methods: A structured literature review was conducted to identify human experimental studies published through August, 2012. Thirty-three studies (1957-2012) evaluating the effects of air ionization on depression, anxiety, mood states, and subjective feelings of mental well-being in humans were included. Five studies on negative ionization and depression (measured using a structured interview guide) were evaluated by level of exposure intensity (high vs. low) using meta-analysis.

Results: Consistent ionization effects were not observed for anxiety, mood, relaxation/sleep, and personal comfort. In contrast, meta-analysis results showed that negative ionization, overall, was significantly associated with lower depression ratings, with a stronger association observed at high levels of negative ion exposure (mean summary effect and 95% confidence interval (CI) following high- and low-density exposure: 14.28 (95% CI: 12.93-15.62) and 7.23 (95% CI: 2.62-11.83), respectively). The response to high-density ionization was observed in patients with seasonal or chronic depression, but an effect of low-density ionization was observed only in patients with seasonal depression. However, no relationship between the duration or frequency of ionization treatment on depression ratings was evident.

Conclusions: No consistent influence of positive or negative air ionization on anxiety, mood, relaxation, sleep, and personal comfort measures was observed. Negative air ionization was associated with lower depression scores particularly at the highest exposure level. Future research is needed to evaluate the biological plausibility of this association.

Figure 1

High-Density Negative Air Ion Exposure and Depression. *Includes data from studies at the last follow-up time point where applicable [6-8]; p for heterogeneity (composite SIGH-SAD) = 0.94. CI: Confidence Interval; SIGH-SAD: Structured Interview Guide for the Hamilton Depression Rating Scale, Seasonal Affective Disorders.

Figure 2

Low-Density Negative Air Ion Exposure and Depression. *Includes data from studies at the last follow-up time point where applicable [6-8]; p for heterogeneity (composite SIGH-SAD) < 0.0001. CI: Confidence Interval; SIGH-SAD: Structured Interview Guide for the Hamilton Depression Rating Scale, Seasonal Affective Disorders.

Figure 3

Dose–response Assessment Between Exposure Duration as Measured by Hours, within High-Density Air Ion Levels, and Each Study’s Score Mean Difference. *Terman, 1998 [8] only provided data for the composite SIGH-SAD scale and not by subscale; Terman and Terman [6] only provided data by subscale and not for the composite SIGH-SAD scale.

Figure 4

Visual Assessment of Publication Bias Using a Funnel Plot (SIGH-SAD composite scores). *A clustering indicative of publication bias around the mean treatment effect was not observed (i.e., no marked asymmetry was evident). In the absence of publication bias we would expect the studies to be distributed symmetrically about the combined treatment effect.