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Chronic noise exposure and testosterone deficiency -- meta-analysis and meta-regression of experimental studies in rodents.

INTRODUCTION
Chronic psychological distress can cause suppression of the hypothalamic-pituitary-testicular axis and thus lead to male hypogonadism, which is associated with psycho-social dysfunction, chronic diseases, and as a result, considerable economic costs. Conversely, noise is a prototypal environmental stressor of growing importance, already linked to birth outcomes and diabetes. However, its effects on male testosterone levels have been paid little attention.


MATERIAL AND METHODS
This paper reports a systematic review and meta-analysis of experimental studies in rodents, which have examined the effect of chronic noise stress on serum testosterone levels. A systematic search in MEDLINE, EMBASE and the Internet yielded seven studies. A quality effects meta-analytical model was applied to compute pooled Hedges's g. Quality effects meta-regression was carried out as well.


RESULTS
We found pooled Hedges's g of -2.41 (95% CI: -3.28, -1.54), indicating a very large effect of noise exposure on testosterone. Metaregression confirmed that the overall duration of exposure explained a significant proportion of the variance across individual effect sizes (Q (1) = 3.95, p = 0.047). However, there was considerable inter-study heterogeneity (I2 = 82%) and publication bias (p = 0.016). After inputting two studies previously thought to be missing, the pooled effect dropped to g = -1.53 (95% CI: -3.01, -0.05).


CONCLUSIONS
Chronic noise exposure of ≈ 100 dB leads to a significant reduction of serum testosterone in male rodents. Research on humans is highly warranted, especially given the steady trend in Western societies for increasing the burden of both male hypogonadism and noise pollution.