新的世界卫生组织《全球空气质量指南》近日发布，该指南建议了新的空气质量水平，以便通过降低主要空气污染物的水平来保护人群健康，其中一些污染物还会加剧气候变化。
“炊烟袅袅”常被用于形容悠然闲适的乡野风光，然而“烟”有时往往也意味着室内空气污染的产生。室内空气污染主要产生于固体燃料（煤炭，草木或动物粪便等）的不完全燃烧，曾经被世界卫生组织（The World Health Organization, WHO）称为世界上最严重的单因素环境污染健康风险。然而在我国，目前仍然有一半的农村人口依赖于固体燃料进行日常的烹饪、取暖等活动。
许多低收入家庭之所以无法跳出贫困陷阱（下图收入S曲线前段），是因为他们无意也无力将现有的资源投入到可以改变现状、提高未来收入的投资中去。因病致贫是导致低收入家庭陷入贫困陷阱的重要因素之一——由于疾病而造成的健康损失降低了未来预期收入，从而使得人力资本提升的可能性更低，低收入家庭更难以跳出贫困的怪圈。为了更有效地巩固脱贫攻坚的成果、推进乡村振兴的目标，理解和评估固体燃料的使用和社会经济因素的关系及其对健康造成的风险就显得尤为重要。
近日，清华大学万科公共卫生与健康学院副教授纪思翰（John S. Ji）教授及其团队与四川省疾病预防控制中心在《国际流行病学杂志》（International Journal of Epidemiology）合作发表文章“固体燃料使用、社会经济因素和心血管疾病及全因死亡率：基于中国四川农村地区的前瞻性研究”（Solid fuel use, social-economic indicators, and risk of cardiovascular diseases and all-cause mortality: a prospective cohort study ina rural area of Sichuan, China）。
文章首先使用了Cox比例风险回归模型，估计了固体燃料对心血管疾病和全因死亡率的影响。然后使用中介效应模型对社会经济因素（教育和家庭收入）、固体燃料的使用情况以及心血管疾病和全因死亡率三者之间的关系进行了分析。对于前两组分析中结果显著的关系组合，文章还进一步分析了停用固体燃料或改用清洁燃料（电或天然气）烹饪或取暖的补救行为对于相关死亡率的影响。
研究发现，与基线时使用清洁燃料烹饪或取暖的人群相比，使用固体燃料的人群有更高的全因死亡风险。另外，使用固体燃料在冬天取暖的人群比使用清洁燃料的人群有更高的心脑血管疾病和中风致死的风险。
在中介效应分析中，研究发现低教育水平对全因死亡率的影响中，42.4%可以由用于烹饪的固体燃料解释，81.1%可以由用于冬季取暖的固体燃料的使用解释。而用于烹饪和取暖的固体燃料也可以分别解释55.2%和76.0%的低收入水平对全因死亡率的影响。研究还发现，在使用固体燃料的人群中，后期停用或改用清洁燃料的人群有更低的心血管疾病和全因死亡风险。这一发现将有助于制定更加精准的扶贫政策——为避免人群因贫困致病而陷入贫困陷阱，改善家庭燃料使用情况或许是一个低成本但有效的解决办法。
Estimates indicate that household air pollution caused by solid fuel burning accounted for about 1.03 million premature mortalities in China in 2016. In the country’s rural areas, more than half the population still relies on biomass fuels and coals for cooking and heating. Understanding the health impact of indoor air pollution and socioeconomic indicators is essential for the country to improve its developmental targets.We aimed to described emographic and socio-economic characteristics associated with solid fuel users in a rural area in China. We also estimated the risk of cardiovascular diseaseand all-cause mortality in association with solid fuel use and described the relationship between solid fuel use, socioeconomic status, and mortality. We also measured the risk of long-term use and the effect of ameliorative action on mortality caused by cardiovascular disease and other causes.We used the China Kadoorie Biobank (CKB) site in Pengzhou, Sichuan, China. We followed a cohort of 55 687 people from 2004-2013. We calculated the mean and standard deviation among subgroups classified by fuel use types: gas, coal, wood, and electricity(central heating additionally for heating). We tested the mediation effect using the stepwise method and Sobel-test. We used Cox proportional models to estimate the risk of incidences of cardiovascular disease and mortality with survival days as the time scale, adjusted for age, gender, socioeconomic status, physical measurements, lifestyle, stove ventilation, and fuel type used for the other purpose. The survival days were defined as the follow-up days from the baseline survey till the date of death, or 31 December 2013 if right-censored. We also calculated the absolute mortality rate difference (ARD) between the exposure group and the reference group.The study population had anaverage age of 51.0, and 61.8% of the individuals were female. 64.8% participants (n=35543) cooked regularly and 25.4% participants (n=13921) needed winter heating. With clean fuel users as the reference group, participant households that used solid fuel for cooking or heating both had a higher riskof all-cause mortality (hazard ratio [HR] for: Cooking, 1.11 [95% CI,1.01-1.26]; Heating, 1.34 [95% CI, 1.16-1.54]). Solid fuel used for winter heating was associated with a higher risk of mortality caused by cerebrovascular disease (HR: 1.64 [95% CI, 1.12-2.40]), stroke (HR: 1.70 [95%CI, 1.13-2.56]), and cardiovascular disease (HR: 1.49 [95% CI, 1.10-2.02]). Low income and poor education level had a significant correlation with solid fuelused for cooking (odds ratio [OR] for Income, 2.27 [95% CI, 2.14-2.41];Education, 2.34 [95% CI, 2.18-2.53]) and heating (OR for Income, 2.69 [95% CI,2.46-2.97]; Education, 2.05 [95% CI, 1.88-2.26]), which may be potential mediators bridging the effect of socioeconomic status factors on cardiovascular disease and all-cause mortality. Solid fuel used for cooking and heating accounted for 42.4% and 81.1% of the effect of poor education and 55.2% and 76.0% of the effect of low income on all-cause mortality respectively. The risk of all-cause mortality could be ameliorated by stopping regularly cooking and heating using solid fuel or switching from solid fuel to clean fuels (HR forCooking, 0.90 [95% CI, 0.84-0.96]; Heating: 0.76 [95% CI, 0.64-0.92]).Our study reinforces the evidence of an association between solid fuel use and risk of cardiovascular disease and all-cause mortality. We also assessed the effect of socioeconomic status as the potential mediator on mortality. As solid fuel use was a major contributor in the effect of socioeconomic status on cardiovascular disease and all-cause mortality, policies to improve access to clean fuels could reduce morbidity and mortality related to poor education and low income.Keywords: Cardiovascular Disease, Biomass Fuel, Mediation Analysis, Social Economic Indicator
John S. Ji 纪思翰
■ 清华万科卫健学院副教授
■ 研究方向：环境流行病学，神经流行病学，老龄化，长寿，环境基因交互，植被，空气污染，重金属，气候变化
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新的世界卫生组织《全球空气质量指南》载有明确证据表明，空气污染有害人类健康，甚至在低于以往所知的浓度水平也会导致损害。该指南建议了新的空气质量水平，以便通过降低主要空气污染物的水平来保护人群健康，其中一些污染物还会加剧气候变化。
空气污染是人类健康面临的最大环境威胁之一，与气候变化并列。改善空气质量可以加强减缓气候变化的努力，而减少排放反之也可改善空气质量。如能力争达到新指南规定的水平，各国将既能保护健康又能减缓全球气候变化。
世卫组织的新指南针对六种污染物建议了空气质量水平，因为关于接触这六种污染物导致的健康影响的证据最多。当对这些所谓的传统污染物，即颗粒物(PM)、臭氧（O₃）、二氧化氮（NO₂）、二氧化硫（SO₂）和一氧化碳（CO）采取行动时，也可对其他有害污染物产生影响。
世卫组织总干事谭德塞博士说：“空气污染是所有国家都面临的一项健康威胁，但其对低收入和中等收入国家人群的影响最大。世卫组织的新《空气质量指南》是一个基于证据的实用工具，可帮助改善所有生命赖以生存的空气质量。我促请所有国家以及所有奋力保护我们的环境的人们利用该指南来减少痛苦和挽救生命。”
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