Abstract：
Forest environment has many health benefits, and negative air ions (NAI) is one of the major forest environmental factors. Many studies have explored the effect of forest environment on cardiac autonomic nervous function, while forest NAI in the among function and the underlying mechanism still remain unclear. To explore the associations and molecular linkages between short-term exposure to forest NAI and heart rate variability (HRV), a repeated-measure panel study was conducted among 31 healthy adults. Participants were randomly selected to stay in a forest park for 3 days and 2 nights. Individual exposures including NAI were monitored simultaneously and HRV indices were measured repeatedly at the follow-up period. Urine samples were collected for non-targeted metabolomics analysis. Mixed-effect models were adopted to evaluate associations among NAI, HRV indices and metabolites. The median of NAI concentration was 68.11 (138.20) cm-3 during the study period. Short-term exposure to forest NAI was associated with the ameliorative HRV indices, especially the excitatory parasympathetic nerve. For instance, per interquartile range increase of 5-min moving average of NAI was associated with 9.99 % (95%CI: 8.95 %, 11.03 %) increase of power in high frequency. Eight metabolites were associated with NAI exposure. The down-regulated tyrosine metabolism was firstly observed, followed by other amino acid metabolic alterations. The NAI-related metabolic changes reflect the reduction of inflammation and oxidative stress. HRV indices were associated with 25 metabolites, mainly including arginine, proline and histidine metabolism. Short-term exposure to forest NAI is beneficial to HRV, especially to the parasympathetic nerve activity, by successively disturbing different metabolic pathways which mainly reflect the increased anti-inflammation and the reduced inflammation. The results will provide epidemiological evidences for developing forest therapy and improving cardiac autonomic nervous function.
摘要：
森林环境有许多健康益处，空气负离子(NAI)是主要的森林环境因子之一。许多研究探索了森林环境对心脏自主神经功能的影响，而森林NAI在其中的功能和潜在机制仍不清楚。探讨短期暴露于森林NAI与心率变异性（HRV）之间的关联和分子联系，我们在31名健康成人中进行了一项重复测量小组研究.随机选择参与者在森林公园停留3天2夜。同时监测包括NAI在内的个体暴露，并在随访期间重复测量HRV指数。收集尿样用于非靶向代谢组学分析。采用混合效应模型来评估NAI之间的关联，HRV指数和代谢物。研究期间NAI浓度的中值为68.11(138.20)cm-3。短期暴露于森林NAI与改善的HRV指数有关，尤其是兴奋性副交感神经.例如,NAI的5分钟移动平均值的每四分位数间距增加与9.99%相关(95CI：8.95%，11.03%）高频功率增加。8种代谢物与NAI暴露有关。首先观察到下调的酪氨酸代谢，其次是其他氨基酸代谢改变。NAI相关的代谢变化反映了炎症和氧化应激的减少。HRV指数与25种代谢物相关，主要包括精氨酸,脯氨酸和组氨酸代谢。短期接触森林NAI有利于HRV，尤其是副交感神经活动，通过连续干扰不同的代谢途径，这些途径主要反映了抗炎作用的增加和炎症的减少。该结果将为开展森林疗法和改善心脏自主神经功能提供流行病学依据。
