Environmental risk factors, particularly air pollution, have been associated with increased risk of neurological disorders. In 2017, The Lancet Commission on pollution and health reported that all types of pollution (ie, air, water, soil, chemical, and occupational pollutants) is the world’s largest environmental cause for poor health, responsible for about 9 million deaths in 2015—16% of all deaths globally. Exploring, understanding, and preventing the effects of sustained exposure to air pollutants on the brain, and possible links to diseases of the nervous system, will be one of the future challenges for global health, and was the topic of discussion at the 2nd International Meeting on Environmental Health, held Nov 29–Dec 1, 2017, in Strasbourg, France. Air pollution is recognised as a global public health issue: the Global Burden of Diseases, Injuries, and Risk Factors (GBD) Study reported that air pollution alone was responsible for 6∙7 million deaths globally in 2016. Furthermore, the number of deaths is expected to more than double by 2050 if no action is taken. Low-income and middle-income countries bear the largest disease burden, as reported in The Lancet Commission, with almost 92% of all pollution-related deaths occurring in these regions. However, a first bright spot in the field was a 23% reduction in the age-standardised death rates for all causes of air pollution between 2006 and 2016. Although neurological effects attributable to air pollution have been shown in several studies, global data on the effects of air pollution exposure on the brain are absent. That air pollution might cause 30% of all strokes, and thus might be one of the leading contributors of the global stroke burden, was highlighted in an analysis of stroke and risk factors from the Global Burden of Disease Study 2013. The mechanism of action is most likely a direct effect of particulate matter—a mixture of solid particles and liquid droplets found in the air and in gases such as ozone and nitrogen dioxide—on the vascular system, causing oxidative stress and inflammation. Even if the neurological effect attributable to exposure to air pollutants on an individual might be small to modest, the overall attributable risk might be considerably higher, given that a large proportion of the population is exposed to air pollutants. Whether air pollution also affects dementia, the second largest neurological cause of disability-adjusted life-years according to the GBD 2015 Study, is less clear. Recent epidemiological studies and animal models suggest an increased risk of dementia with sustained exposure to air pollutants, but the underlying mechanisms are unclear and potential confounding factors such as including lifestyle factors (eg, diet, physical activities) and medical history cannot be excluded. However, given the strong association between stroke, vascular risk factors, and dementia, the suggested link between air pollution and dementia is to be expected. Neurological disorders represent the largest cause of disability-adjusted life-years and the secondlargest cause of global deaths behind cardiovascular diseases, as highlighted in the GBD 2015 Study. Thus, the potential negative effects of environmental pollution on neurological health should receive more attention from researchers, funders, regulators, and governments. Even though—with the exception of stroke—definitive conclusions on the neurological effects associated with sustained exposure to air pollution cannot be arrived at from current knowledge, given the broader health issues, implementation of policies that seek to improve air pollution should be a priority for governments. The United Nations and WHO have both been driving forces in improving air quality and have launched several pollution-reducing action plans. For example, WHO has developed indoor and outdoor air quality guidelines, and “the investigation of health impacts of climate and environmental change” is one of the top four WHO health priorities. The United Nations’ 2030 Agenda for Sustainable Development—a set of 17 goals established to achieve global sustainable development by 2030— recognises air pollution as the greatest environmental health risk, and it is likely that pollution control will have positive effects on many of these goals and on neurological health. The good news is that air pollution can be controlled and that the growing recognition of air pollution as a potential contributor to neurological disease is promising for improved brain health. Improvements now need to be made in study design and measurement of air pollution to enable more reliable and accurate estimates about the possible negative effects on brain health, beyond those on cerebrovascular disease.

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空气污染和大脑健康：一个新出现的问题

环境风险因素，尤其是空气污染，与神经系统疾病的风险增加有关。2017 年，柳叶刀污染与健康委员会报告称，所有类型的污染（即空气、水、土壤、化学和职业污染物）是世界上导致健康不佳的最大环境原因，2015 年造成约 900 万人死亡——占全球所有死亡人数的 16%。探索、了解和预防持续暴露于空气污染物对大脑的影响，以及与神经系统疾病的可能联系，将是全球健康的未来挑战之一，也是第二届国际会议的讨论主题2017 年 11 月 29 日至 12 月 1 日在法国斯特拉斯堡举行。空气污染被认为是一个全球公共卫生问题：全球疾病负担，伤害和风险因素 (GBD) 研究报告称，2016 年仅空气污染就造成全球 6.7 万人死亡。此外，如果不采取行动，预计到 2050 年死亡人数将增加一倍以上。正如柳叶刀委员会所报告的那样，低收入和中等收入国家承担着最大的疾病负担，几乎 92% 的与污染相关的死亡发生在这些地区。然而，该领域的第一个亮点是 2006 年至 2016 年期间所有空气污染原因的年龄标准化死亡率降低了 23%。空气污染暴露对大脑的影响不存在。空气污染可能导致 30% 的中风，2013 年全球疾病负担研究中对中风和风险因素的分析中强调了这一点，因此可能是全球中风负担的主要贡献者之一。 作用机制很可能是颗粒物质的直接影响 - 一种混合物空气中以及臭氧和二氧化氮等气体中的固体颗粒和液滴对血管系统造成氧化应激和炎症。即使暴露于空气污染物对个人的神经系统影响可能很小到中等，但考虑到很大比例的人口暴露于空气污染物，总体归因风险可能会高得多。根据 GBD 2015 研究，空气污染是否也会影响痴呆症，这是导致残疾调整生命年的第二大神经原因，不太清楚。最近的流行病学研究和动物模型表明，持续暴露于空气污染物会增加患痴呆症的风险，但潜在的机制尚不清楚，并且不能排除潜在的混杂因素，例如生活方式因素（如饮食、体育活动）和病史。然而，考虑到中风、血管危险因素和痴呆症之间的密切关联，空气污染与痴呆症之间的建议联系是可以预料的。正如 GBD 2015 研究所强调的那样，神经系统疾病是导致残疾调整生命年的最大原因，也是仅次于心血管疾病的全球第二大死亡原因。因此，环境污染对神经系统健康的潜在负面影响应该受到研究人员、资助者、监管机构、和政府。尽管——除了中风——关于与持续暴露于空气污染相关的神经系统影响的确定性结论无法根据目前的知识得出，但考虑到更广泛的健康问题，实施旨在改善空气污染的政策应该是优先事项政府。联合国和世卫组织一直在推动改善空气质量，并推出了多项减少污染的行动计划。例如，世卫组织制定了室内外空气质量指南，“气候和环境变化对健康影响的调查”是世卫组织四大卫生重点之一。联合国 2030 年可持续发展议程——为到 2030 年实现全球可持续发展而制定的 17 个目标——承认空气污染是最大的环境健康风险，污染控制很可能会对其中许多目标产生积极影响和神经系统健康。好消息是空气污染是可以控制的，而且人们越来越认识到空气污染是导致神经系统疾病的潜在因素，这有望改善大脑健康。现在需要改进空气污染的研究设计和测量，以便更可靠和准确地估计对脑健康可能产生的负面影响，而不是对脑血管疾病的负面影响。污染控制很可能会对其中许多目标和神经系统健康产生积极影响。好消息是空气污染是可以控制的，而且人们越来越认识到空气污染是导致神经系统疾病的潜在因素，这有望改善大脑健康。现在需要改进空气污染的研究设计和测量，以便更可靠和准确地估计对脑健康可能产生的负面影响，而不是对脑血管疾病的负面影响。污染控制很可能会对其中许多目标和神经系统健康产生积极影响。好消息是空气污染是可以控制的，而且人们越来越认识到空气污染是导致神经系统疾病的潜在因素，这有望改善大脑健康。现在需要改进空气污染的研究设计和测量，以便更可靠和准确地估计对脑健康可能产生的负面影响，而不是对脑血管疾病的负面影响。