Evidence indicates that living in areas of high greenness is associated with lower rates of cardiovascular and all-cause mortality.¹ However, specific health-promoting characteristics of greenness have not been identified, and how greenness interacts with the surrounding ecology to promote human health remains unclear. Identifying the vegetation type, characteristics, and extent of greenness that is most beneficial for health is necessary to optimize its health impact, especially as the climate continues to change. The landmass of the contiguous United States encompasses diverse ecosystems ranging from deserts and evergreen forests to coastal plains and prairies. These diverse areas of common ecological characteristics, known as ecoregions, could directly impact the health of the population as well as modify the beneficial impact of greenness on health. Therefore, we categorized areas of similar ecosystems by level I ecoregions and their more detailed nested level II ecoregions to assess how they modify the relationship between greenness and mortality.

County-level age-adjusted mortality rates in adults >35 years of age (per 100 000) for the contiguous United States were obtained from the CDC via the Interactive Atlas of Heart Disease and Stroke and CDC WONDER (n=2946). Deaths were classified by the International Classification of Diseases, Tenth Revision (ICD-10) codes for all-cause mortality, total cardiovascular disease (CVD) mortality (ICD-10: I00-I78), ischemic heart disease (IHD) mortality (ICD-10: I20-I25), and cerebrovascular disease mortality (ICD-10: I60-I69). Data were extracted and pooled within 2 time periods (2008 to 2010 and 2018 to 2020).

County-level greenness was estimated by the enhanced vegetation index (EVI), obtained from Moderate Resolution Imaging Spectroradiometer (MODIS) at a spatial resolution of 250 meters for the summer months (June to August) in 2 time periods (2008 to 2010 and 2018 to 2020) via Google Earth Engine. EVI corrects for aerosol effects and allows for higher sensitivity in densely vegetated areas, compared with normalized difference vegetation index (NDVI). We assigned counties to EPA level I and level II ecoregions by their centroid (Figure [A]).² The final analysis included 5 level I ecoregions and 11 nested level II ecoregions. County-level covariates were obtained for the years 2010 and 2020 from the CDC National Environmental Public Health Tracking Network. The average PM_2.5 concentration was obtained from the Center for Air, Climate, and Energy Solutions.³

Figure. The association between greenness and mortality by ecoregion indicated on maps of contiguous United States. Maps for (A) Environmental Protection Agency (EPA) level I and (B) level II ecoregions in the contiguous United States. Data were downloaded from the EPA (https://www.epa.gov/eco-research/ecoregions-north-America) and produced using R (version 4.1.1). C, Association between enhanced vegetation index (EVI) and age-adjusted mortality rates by EPA level 1 and nested level II ecoregions. Level I ecoregion labels are in uppercase, with their corresponding nested level II regions immediately below. Values are % difference in age-adjusted mortality rates and 95% CIs per 1 SD (EVI SD=0.13). Linear-mixed models (n=3032 counties) were adjusted for % smoking, % poverty, % HS education, % White population, % male, % alcohol use, population density, % obese, Rural-Urban Continuum Codes (RUCC; 3 groups), year (2010 and 2020), and PM_2.5. CVD indicates cardiovascular disease; and IHD, ischemic heart disease.

Covariate-adjusted longitudinal associations between greenness and mortality rates were analyzed using a linear-mixed model with a random intercept and slope, clustered by ecoregion (see figure legend for model adjustments).

We observed negative associations between greenness (EVI) and all-cause, CVD, IHD, and cerebrovascular mortality rates in the Great Plains. Moreover, EVI was negatively associated with CVD and IHD mortality in the Eastern Temperate Forests ecoregion (Figure [C]). EVI was also negatively associated with cerebrovascular disease mortality in the Northern Forests. In contrast to these findings, we found some evidence of positive trends in several ecoregions.

Within the Eastern Temperate Forests, the negative association of EVI with CVD was most predominant within the nested Ozark/Ouachita-Appalachian Forests Level II ecoregion (−8.2% per 1 SD [95% CI, −10.6 to −5.7]) and to a lesser extent in the Central United States plains region (Figure [C]). For IHD mortality, we found a negative association with EVI in the Central United States plains region (−5.0% per 1 SD [95% CI, −7.6 to −2.5). EVI was also negatively associated with cerebrovascular mortality in the Ozark/Ouachita-Appalachian Forests and Mixed Wood Plains regions. We consistently found positive associations between EVI and mortality outcomes in the Mississippi Alluvial and Southeast United States Coastal Plains region (% differences ranged from 5.3% to 9.3% per 1 SD).

Within the Great Plains ecoregion, the negative association between EVI and all-cause mortality was driven by the Level II South Central Semi-Arid Prairies ecoregion (−2.0% per 1 SD [95% CI, −3.3 to −0.6]). The negative associations of EVI with CVD and cerebrovascular mortality were the strongest in the Temperate Prairies, although the association with IHD mortality was driven by the South Central Semi-Arid Prairies.

Within the Northern Forests, we observed negative associations between EVI and CVD mortality (−2.84 per 1 SD [95% CI, −5.0 to −0.7]) and IHD mortality (−6.4% per 1 SD [95% CI, −9.9 to −2.8]) in the Mixed Wood Shield level II ecoregion.

We found that the effects of greenness on mortality vary among ecoregions. Higher levels of greenness were associated with lower mortality rates, primarily within the Eastern Temperate Forests and Great Plains regions. However, we found positive associations in other areas. Reasons for such adverse associations remain unclear but may be related to the effects of ecoregion-specific adverse environmental conditions such as air pollution,⁴ heat, humidity, agriculture, etc, which may offset the beneficial effects of greenness. Vegetation also emits pollen, which could adversely affect health, and biogenic volatile organic compounds, which could increase ground-level ozone. Although we cannot rule out sociopolitical or cultural influence in our results, these findings likely represent ecosystem-related variations in the impact of greenness on mortality. Additional studies are needed to further identify specific features of each ecoregion that affect human health at an individual level, and how these relationships vary with seasons and features of the built environment. The findings of our studies could inform the assessment of the public health impact of vegetation, which may vary by ecosystem.

The data that support the findings of this study are available from the corresponding author upon reasonable request.

This work was supported, in part, by grants from the National Institute of Environmental Health Sciences (ES029846, ES023716, and ES030283). This article is the responsibility of the authors and does not represent the official views of the National Institutes of Health.

Nonstandard Abbreviations and Acronyms

CVD	cardiovascular disease
EVI	enhanced vegetation index
IHD	ischemic heart disease

cardiovascular disease

enhanced vegetation index

ischemic heart disease

Disclosures None.

For Sources of Funding and Disclosures, see page 1223.

中文翻译：

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绿色生态区分布与心血管死亡率的关联：美国的一项纵向生态学研究

有证据表明，生活在高绿化地区与较低的心血管死亡率和全因死亡率相关。¹然而，绿色促进健康的具体特征尚未确定，绿色如何与周围生态相互作用以促进人类健康仍不清楚。确定对健康最有益的植被类型、特征和绿色程度对于优化其对健康的影响至关重要，特别是在气候持续变化的情况下。美国本土拥有多样化的生态系统，从沙漠和常绿森林到沿海平原和草原。这些具有共同生态特征的不同区域，称为生态区，可以直接影响人口的健康，并改变绿色对健康的有益影响。因此，我们按一级生态区及其更详细的嵌套二级生态区对类似生态系统的区域进行分类，以评估它们如何改变绿度和死亡率之间的关系。

美国本土 35 岁以上成年人（每 10 万人）的县级年龄调整死亡率是通过心脏病和中风交互式地图集和 CDC WONDER 从 CDC 获得的（n=2946）。死亡按照国际疾病分类第十次修订版( ICD-10 ) 代码进行分类，包括全因死亡率、心血管疾病 (CVD) 总死亡率 ( ICD-10：I00-I78)、缺血性心脏病 (IHD) 死亡率 ( ICD) -10：I20-I25）和脑血管疾病死亡率（ICD-10：I60-I69）。数据是在 2 个时间段（2008 年至 2010 年和 2018 年至 2020 年）内提取和汇总的。

县级绿化度通过增强植被指数（EVI）估算，该指数是通过中分辨率成像光谱仪（MODIS）在2个时间段（2008年至2010年和2018年）夏季（6月至8月）250米空间分辨率下获得的到 2020 年）通过 Google Earth Engine。与归一化植被指数 (NDVI) 相比，EVI 可以校正气溶胶影响，并在植被茂密的地区具有更高的灵敏度。我们根据质心将县划分为 EPA 一级和二级生态区（图 [A]）。²最终分析包括5个一级生态区和11个嵌套二级生态区。 2010 年和 2020 年县级协变量是从 CDC 国家环境公共卫生跟踪网络获得的。 PM _2.5平均浓度来自空气、气候和能源解决方案中心。³

数字。 美国本土地图上按生态区域显示的绿色度与死亡率之间的关联。美国本土( A ) 环境保护局 (EPA) I 级和 ( B ) II 级生态区的地图。数据从 EPA (https://www.epa.gov/eco-research/ecoregions-north-America) 下载并使用 R（版本 4.1.1）生成。C，EPA 1 级和嵌套 II 级生态区增强植被指数 (EVI) 与年龄调整死亡率之间的关联。 I 级生态区域标签为大写，其相应的嵌套 II 级区域紧邻其下。数值为年龄调整死亡率的百分比差异和每 1 SD 的 95% CI（EVI SD=0.13）。线性混合模型（n = 3032 个县）根据吸烟百分比、贫困百分比、高中教育百分比、白人人口百分比、男性百分比、饮酒百分比、人口密度、肥胖百分比、城乡连续代码（RUCC；3 组）进行调整）、年份（2010 年和 2020 年）和 PM _2.5。 CVD表示心血管疾病；和IHD，缺血性心脏病。

使用具有随机截距和斜率的线性混合模型分析了绿度和死亡率之间的协变量调整纵向关联，并按生态区进行聚类（模型调整参见图例）。

我们观察到大平原的绿度 (EVI) 与全因死亡率、CVD、IHD 和脑血管死亡率之间呈负相关。此外，在东部温带森林生态区，EVI 与 CVD 和 IHD 死亡率呈负相关（图 [C]）。 EVI 还与北部森林的脑血管疾病死亡率呈负相关。与这些发现相反，我们在几个生态区发现了一些积极趋势的证据。

在东部温带森林中，EVI 与 CVD 的负相关在嵌套的奥索卡/沃希托-阿巴拉契亚森林 II 级生态区内最为显着（−8.2% 每 1 SD [95% CI，−10.6 至 −5.7]），并且与美国中部平原地区的范围较小（图[C]）。对于 IHD 死亡率，我们发现美国中部平原地区的 EVI 呈负相关（每 1 个 SD -5.0% [95% CI，-7.6 至 -2.5）。在奥扎克/沃希托-阿巴拉契亚森林和混合林平原地区，EVI 还与脑血管死亡率呈负相关。我们一致发现，密西西比冲积层和美国东南部沿海平原地区的 EVI 与死亡率呈正相关（每 1 个标准差百分比差异范围为 5.3% 至 9.3%）。

在大平原生态区内，EVI 与全因死亡率之间的负相关是由二级中南半干旱草原生态区驱动的（−2.0% 每 1 SD [95% CI，−3.3 至 −0.6]）。 EVI 与 CVD 和脑血管死亡率的负相关性在温带草原最为强烈，尽管与 IHD 死亡率的相关性是由中南部半干旱大草原驱动的。

在北部森林内，我们观察到 EVI 与 CVD 死亡率（每 1 个标准差 -2.84 [95% CI，-5.0 至 -0.7]）和 IHD 死亡率（每 1 个标准差 -6.4% [95% CI，-9.9 至 -9.9]）之间呈负相关。 −2.8]）位于混合木盾二级生态区。

我们发现，绿色对死亡率的影响因生态区域而异。较高的绿化水平与较低的死亡率相关，主要是在东部温带森林和大平原地区。然而，我们在其他领域发现了积极的关联。这种不利关联的原因尚不清楚，但可能与生态区特定不利环境条件的影响有关，如空气污染、⁴高温、湿度、农业等，这可能抵消绿色的有益影响。植被还排放花粉，这可能对健康产生不利影响，以及生物挥发性有机化合物，这可能会增加地面臭氧。尽管我们不能排除结果中的社会政治或文化影响，但这些发现可能代表了生态系统相关的绿色对死亡率影响的变化。需要进行更多研究来进一步确定每个生态区在个体层面上影响人类健康的具体特征，以及这些关系如何随季节和建筑环境特征而变化。我们的研究结果可以为评估植被对公共健康的影响提供信息，这可能因生态系统而异。

支持本研究结果的数据可根据合理要求从通讯作者处获得。

这项工作部分得到了以下机构的资助：国家环境健康科学研究所（ES029846、ES023716 和 ES030283）。本文由作者负责，并不代表美国国立卫生研究院的官方观点。

非标准缩写词和首字母缩略词

CVD	心血管疾病
埃维	增强植被指数
内出血	缺血性心脏病

心血管疾病

增强植被指数

缺血性心脏病

披露无。

有关资金来源和披露信息，请参阅第 1223 页。