Air Pollution and Mortality in the Elderly in Kerman, Iran

AUTHORS

Zahra Askari Baravati 1 , Narges Khanjani ORCID 2 , * , Mohammad Malakootian 3

1 Department of Epidemiology and Statistics, Faculty of Public Health, Kerman University of Medical Sciences, Kerman, Iran

2 Environmental Health Engineering Research Center, Kerman University of Medical Sciences (KMU), Kerman, Iran

3 Kerman University of Medical Sciences, Kerman, Iran

How to Cite: Askari Baravati Z, Khanjani N, Malakootian M . Air Pollution and Mortality in the Elderly in Kerman, Iran. Health Scope. 2021;10(2):e105567. doi: 10.5812/jhealthscope.105567.

ARTICLE INFORMATION

Health Scope: 10 (2); e105567
Published Online: July 17, 2021
Article Type: Research Article
Received: May 23, 2020
Revised: April 20, 2021
Accepted: May 27, 2021
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Abstract

Background: Today, air pollution is a major issue in the world, particularly in metropolitan areas.

Objectives: Accordingly, this study aimed to investigate the relation between air pollution and mortality in the elderly in Kerman City.

Methods: This ecological study was conducted using 2006 - 2013 mortality data inquired from the Deputy of Health of Kerman University of Medical Sciences. The data on cardiovascular and respiratory mortality, as well as death due to trauma, diabetes, and other diseases that happened in men and women aged 60 and higher were extracted. Air pollution data (CO, SO2, O3, NO, NO2, NOx, and PM10) for the same time frame were inquired from the Environmental Protection Agency of Kerman Province. Negative binomial regression was used to evaluate the relation between air pollutants and mortality using STATA13 software.

Results: During the study period, a total of 14,793 deaths occurred in elderly men and women in Kerman City. Cardiovascular diseases were the leading cause of death. The results of multivariate analysis of air pollutants indicated that NO was directly and significantly related to the total number of deaths in the elderly, and increase in sulfur dioxide, ozone and NO was significantly related to increased mortality among elderly women. Carbon monoxide was significantly related to cardiovascular death of the elderly. But air pollutants did not show any significant effect on respiratory-, trauma-, and diabetes-related deaths.

Conclusions: Our findings indicate that there is a significant relation between air pollution and mortality in the elderly. Accordingly, a warning system is suggested to reduce the elderly’s commuting on highly air polluted days.

1. Background

Today, air pollution is one of the major environmental issues in the world’s major cities and is jeopardizing the living conditions of human beings (1, 2). High population growth and increased energy consumption, rapid economic and urban development, expansion of urban traffic, inappropriate use of industrial systems and devices, and non-compliance with environmental regulations has resulted in air pollution in many countries (3).

According to the World Health Organization (WHO), approximately 3 million people lose their lives annually due to air pollution (4). WHO has estimated that exposure to particulate matter causes more than 500,000 premature deaths per year. The numerous adverse events that have occurred as a result of air pollution in the world can appropriately highlight the importance of this issue. In October 1948, sulfur dioxide (SO2) and industrial dust caused the death of 20 people and sickened almost 6,000 people in Pennsylvania. In London in December 1952, burning coal in homes and SO2 emissions along with inversion and air pollution entrapment caused the death of 4000 people. In December 1962, again air pollution in London took the lives of 300 people (3).

It seems air pollution has a very comprehensive impact on human health. The severe effects of carbon monoxide (CO) on human health include increased mortality due to heart and respiratory diseases, stroke, and acute heart attacks. Studies have shown a relation between respiratory diseases and environmental pollution in industrialized countries as well as countries with low or moderate income. Therefore, air pollution is nowadays a major global environmental health problem (5).

One of the groups that are likely to be more susceptible to air pollution is the elderly. A previous analysis of an elderly cohort in Hong Kong revealed that long-term exposure to PM2.5 and black carbon was associated with cardiovascular mortality, but not respiratory mortality, among an elderly population in Hong Kong, a high-density and high-rise city in Asia, and effect estimates remained similar for various time exposure windows (6). Yap et al. (7) conducted a time series study in Singapore and revealed that particulate air pollutants (PM2.5, PM10) were associated with non-accidental mortality and cardiovascular mortality, and the effects were greater on the elderly. Another study in Montreal showed positive associations between daily non-accidental mortality and all air pollutants, except ozone. They also noticed that people with cardiovascular disease, congestive heart failure, atrial fibrillation, diabetes, and cardiovascular disease are more likely to die from air pollution (8).

2. Objectives

This study aimed to investigate the relation between air pollution and elderly death in Kerman, Iran. This was the first study of this kind done in Kerman. Kerman City is one of the major cities of Iran located in the southeast, with a population of over 621,374 individuals according to the 2011 census (9).

3. Methods

This was an ecological study conducted in Kerman city. Initially, data on the number of deaths in the elderly per day, from 2006 until 2013 were inquired from the Deputy of Health of Kerman University of Medical Sciences. Elderly deaths were deaths that occurred due to any reason in people aged 60 and older. Then, these deaths were classified based on gender (male and female) and the cause of death (cardiovascular disease, respiratory diseases, trauma, diabetes, and other diseases).

Data on air pollution (including NO, CO, NO2, NOx, PM10, SO2, and O3) were inquired from the Environmental Protection Agency of Kerman Province. These data are measured on a daily basis using a fixed station within the city. In this study, observations that were more than ± 3 SD away from the mean were recognized as outliers and were dealt with as missing data. Then missing air pollution data were estimated using the expectation-maximization (EM) algorithm in SPSS20 software. Details of these methods can be found in our previous publications (10). This study was approved by the Standing Committee on Ethics in Research of Kerman University of Medical Sciences (ethics code: IR.KMU.REC.1394.428). The relation between daily mortality and air pollution was analyzed using negative binomial regression in STATA13.

4. Results

During this time, 6465, 2958, 1017, 895, and 3458 deaths caused by cardiovascular diseases, respiratory diseases, trauma, diabetes, and other reasons, respectively, occurred among the elderly in Kerman. The numbers of deaths have been categorized on the basis of year and gender in Table 1. The average air pollutants during these seven years are shown in Table 2. The relation between daily levels of air pollutants and deaths in the elderly caused by cardiovascular diseases, respiratory diseases, trauma, diabetes, other diseases as well as the total number of diseases; categorized based on gender have been shown in Tables 3 to 8. The results of multivariate analysis of air pollutants indicated that nitrogen oxide (NO) was directly and significantly related to total numbers of deaths in the elderly; and an increase in SO2, ozone, and NO was significantly related to increased mortality among elderly women (Table 3).

Table 1. The Number of Total Deaths in the Elderly From 2006 to 2013 in Kerman City
Cause of Death2006200720082009201020112012All Years
Cardiovascular diseases
Total118494661998610388208726465
Men6524903044825204344473329
Women5324563155025183864253134
Respiratory diseases
Total4114753253904604993982958
Men2472711902162502722171663
Women1642041351742102271811295
Trauma
Total10694861511222392191017
Men7863579872145137650
Women28312953509482367
Diabetes
Total79169122101129189106895
Men39684948369745382
Women401017353939261513
Other reasons
Total3994353894256066555493458
Men2272552052353463653181951
Women1721801841902602902311507
All deaths
Total217921191541205323552402214414793
Men1243114780510811224131311647977
Women936972736972113110899806817
Table 2. Status of Pollutants in Kerman During 2006 - 2013
PollutantsMedianMeanMinimumMaximumSD
CO, ppm1.011.210.1095.310.70
SO2, ppb7.458.260.1070.304.66
O3, ppb20.1024.171.9182.3016.03
NO, ppb9.3314.060.129413.92
NO2, ppb20.2519.650.1643.317.35
NOx, ppb29.2933.160.20112.5016.69
PM10, µg/m389.90100.681732755.39
Table 3. The Results of Negative Binomial Regression of the Impact of air Pollutants on Overall Deaths Per Day (Ratio of Increased Daily Mortality for Every Unit Increase in Average Daily Emissions)
PollutantCrude IRR* and 95%CIP-ValueAdjusted IRR and 95%CIP-Value
Total
CO, ppb1.02342 (0.99874 - 1.04872)0.0630.98682 (0.94723 - 1.02808)0.526
SO2, ppb1.00477 (1.00072 - 1.00884)0.021a1.00531 (0.99951 - 1.01115)0.073
O3, ppb1.00030 (0.99922 - 1.00138)0.5801.00103 (0.99761 - 1.00446)0.555
NO, ppb1.00371 (1.00230 - 1.00513)< 0.001a1.00335 (1.00010 - 1.00661)0.043a
NO2, ppb1.00162 (0.99827 - 1.00499)0.3420.99643 (0.99120 - 1.00169)00.184
NOx, ppb1.00239 (1.00120 - 1.00359)< 0.001a1.00268 (0.99932 - 1.00604)0.117
PM10, µg/m30.99933 (0.99897 - 0.99969)< 0.001a0.99940 (0.99901 - 0.99980)0.004a
Men
CO, ppb1.04496 (1.01090 - 1.08017)0.009a1.00741 (0.95153 - 1.06656 -0.800
SO2, ppb1.00339 (0.99853 - 1.00827)0.1711.0046 (0.99753 - 1.01187)0.200
O3, ppb0.99925 (0.99777 - 1.00073)0.3241.00574 (0.99856 - 1.00258)0.576
NO, ppb1.00368 (1.00197 - 1.00539)< 0.001a1.00081 (0.99682 - 1.00482)0.688
NO2, ppb0.99979 (0.99731 - 1.00227)0.8690.99441 (0.98799 - 1.00088)0.090
NOx, ppb1.00301 (1.00157 - 1.00445)< 0.001a1.00371 (0.99957 - 1.00787)0.078
PM10, µg/m30.99935 (0.99890 - 0.99981)0.005a0.99922 (0.99877 - 0.99971)0.002a
Women
CO, ppb0.97830 (0.94308 - 1.01484)0.2410.93152 (0.87552 - 0.99110)0.025a
SO2, ppb1.00709 (1.00184 (1.01235)0.008a1.00904 (1.00137 - 1.01678)0.021a
O3, ppb1.00197 (1.00039 - 1.00355)0.015a1.00529 (1.00313 - 1.00980)0.004a
NO, ppb1.00275 (1.00088 - 1.00462)0.004a1.00536 (1.00109 - 1.00964)0.014a
NO2, ppb0.99792 (0.99429 - 1.00156)0.2641.00156 (0.99467 - 1.00851)0.657
NOx, ppb1.00115 (0.99955 - 1.00275)0.1571.000421 (0.99609 - 1.00476)0.849
PM10, µg/m30.99950 (0.99902 - 0.99998)0.044a0.99983 (0.99983 - 1.00036)0.542

Abbreviation: IRR, incidence rate ratio.

aStatistically significant.

Table 4. The Results of Negative Binomial Regression of the Impact of Air Pollutants on Overall Daily Deaths in the Elderly Caused by Cardiovascular Diseases (Ratio of Increased Daily Mortality for Every Unit Increase in Average Daily Emissions)
PollutantCrude IRR* and 95%CIP-ValueAdjusted IRR and 95%CIP-Value
Total
CO, ppm1.05253 (1.01536 - 1.09106)0.005a1.07095 (1.01484 - 1.13016)0.013a
SO2, ppb0.99981 (0.99429 - 1.00536)0.9481.00079 (0.99277 - 1.00889)0.846
O3, ppb0.99927 (0.99764 - 1.00091)0.3871.00061 (0.99838 - 1.00284)0.592
NO, ppb0.99918 (0.99718 - 1.00118)0.4240.99418 (0.98931 - 0.99907)0.020a
NO2, ppb1.00450 (1.00076 - 1.00825)0.018a1.00041 (0.99306 - 1.00781)0.913
NOx, ppb1.00072 (0.99909 - 1.00235)0.3821.00315 (0.99838 - 1.00794)0.195
PM10, µg/m30.99961 (0.99912 - 1.00010)0.1270.99943 (0.99888 - 0.99998)0.043a
Men
CO, ppm1.043605 (0.99352 - 1.09621)0.0891.04287 (0.96880 - 1.12259)0.264
SO2, ppb0.99966 (0.99229 - 1.00709)0.9291.00177 (0.99079 - 1.01286)0.753
O3, ppb0.99955 (0.99724 - 1.00186)0.7041.00016 (0.99704 - 1.00329)0.917
NO, ppb0.99949 (0.99677 - 1.00223)0.7190.99344 (0.98693 - 1.00000)0.050
NO2, ppb1.00368 (0.99850 - 1.00888)0.1640.997842 (0.98784 - 1.007930.674
NOx, ppb1.00132 (0.99911 - 1.00354)0.2391.00521 (0.99884 - 1.0116)0.109
PM10, µg/m30.99961 (0.99891 - 1.00032)0.2890.99947 (0.99869 - 1.00025)0.190
Women
CO, ppm1.02697 (0.97320 - 1.08372)0.3321.05912 (0.97875 - 1.14609)0.154
SO2, ppb1.00617 (0.99755 - 1.01486)0.1611.00583 (0.99402 - 1.01777)0.335
O3, ppb1.00617 (0.99807 - 1.00274)0.7321.00205 (0.998868 - 1.005249)0.207
NO, ppb0.99991 (0.99702 - 1.00281)0.9550.99972 (0.99269 - 1.00679)0.939
NO2, ppb1.00430 (0.99894 - 1.00969)0.1161.00847 (0.99784 - 1.01920)0.119
NOx, ppb1.00044 (0.99804 - 1.00284)0.7180.99862 (0.99183 - 1.00546)0.693
PM10, µg/m31.00002 (0.99932 - 1.00072)0.9471.00018 (0.99941 - 1.00095)0.641

Abbreviation: IRR, incidence rate ratio.

aStatistically significant.

Table 5. The Results of Negative Binomial Regression of the Impact of Air Pollutants on Overall Deaths in the Elderly Caused by Respiratory Diseases (Ratio of Increased Daily Mortality for Every Unit Increase in Average Daily Emissions)
PollutantCrude IRR* and 95%CIP-ValueAdjusted IRR and 95%CIP-Value
Total
CO, ppm1.05663 (1.00238 - 1.11382)0.041a0.99477 (0.91734 - 1.07874)0.899
SO2, ppb1.00368 (0.99590 - 1.01152)0.3541.00865 (0.99667 - 1.02077)0.158
O3, ppb0.99727 (0.99478 - 0.99976)0.032a0.99806 (0.99468 - 1.00145)0.262
NO, ppb1.00369 (1.00090 - 1.00644)0.009a1.00157 (0.99423 - 1.00897)0.675
NO2, ppb1.00388 (0.99844 - 1.00935)0.1620.99992 (0.98939 - 1.01057)0.989
NOx, ppb1.00277 (1.00044 - 1.00510)0.020a1.00028 (0.99316 - 1.00745)0.938
PM10, µg/m30.99971 (0.99897 - 1.00045)0.4440.99949 (0.99867 - 1.00031)0.227
Men
CO, ppm1.05413 (0.98111 - 1.13258)0.1500.98564 (0.88279 - 1.10047)0.797
SO2, ppb0.99802 (0.98609 - 1.01010.7470.99465 (0.97883 - 1.01071)0.512
O3, ppb0.99793 (0.99457 - 1.00131)0.2300.99997 (0.99538 - 1.00458)0.991
NO, ppb1.00343 (0.99978 - 1.00710)0.0651.00021 (0.99070 - 1.00981)0.965
NO2, ppb1.003117 (0.99570 - 1.01058)0.4110.99856 (0.98463 - 1.01268)0.841
NOx, ppb1.00286 (0.99975 - 1.00598)0.0711.00373 (0.99431 - 1.01324)0.438
PM10, µg/m31.00005 (0.99909 - 1.00102)0.9081.00016 (0.99910 - 1.00122)0.767
Women
CO, ppm1.01560 (0.93666 - 1.10118)0.0710.98661 (0.87605 - 1.11113)0.824
SO2, ppb1.00425 (0.99283 - 1.01580)0.4671.00884 (0.99117 - 1.02682)0.329
O3, ppb0.99870 (0.99508 - 1.00249)0.5190.997976 (0.9930014 - 1.00297)0.427
NO, ppb1.00174 (0.99742 - 1.00608)0.4290.99933 (0.98899 - 1.9776)0.900
NO2, ppb0.99979 (0.99163 - 1.00802)0.9610.9940573 (0.97899 - 1.00935)0.444
NOx, ppb1.00089 (0.99727 - 1.00451)0.6301.00041 (0.99053 - 1.01038)0.935
PM10, µg/m30.99928 (0.99813 - 1.00042)0.2190.99921 (0.99794 - 1.00049)0.230

Abbreviation: IRR, incidence rate ratio.

aStatistically significant.

Table 6. The Results of Negative Binomial Regression of the Impact of air Pollutants on Overall Deaths in the Elderly (Men and Women) Caused by Trauma (Ratio of Increased Daily Mortality for Every Unit Increase in Average Daily Emissions)
PollutantCrude IRR* and 95%CIP-ValueAdjusted IRR and 95%CIP-Value
Total
CO, ppm0.92804 (0.84031 - 1.02494)0.1410.87778 (0.75154 - 1.02524)0.100
SO2, ppb0.99915 (0.98549 - 1.01300)0.9040.99995 (0.97762 - 1.02279)0.997
O3, ppb0.99999 (0.99595 - 1.00405)0.9990.99622 (0.99043 - 1.00203)0.203
NO, ppb0.99997 (0.99498 - 1.00498)0.9910.99992 (0.98532 - 1.01475)0.992
NO2, ppb0.99324 (0.98380 - 1.00277)0.1640.99223 (0.97231 - 1.01257)0.452
NOx, ppb0.99908 (0.99475 - 1.00343)0.6811.00025 (0.98591 - 1.01479)0.973
PM10, µg/m30.99979 (0.99858 - 1.00101)0.7450.99946 (0.99806 - 1.00086)0.451
Men
CO, ppm0.92107 (0.81819 - 1.03690)0.1740.90335 (0.74883 - 1.08974)0.288
SO2, ppb0.99778 (0.97893 - 1.01699)0.8200.99750 (0.96807 - 1.02782)0.870
O3, ppb1.00114 (0.99600 - 1.00631)0.6630.99784 (0.99039 - 1.00534)0.573
NO, ppb0.99782 (0.99169 - 1.00398)0.4881.00121 (0.98111 - 1.02172)0.907
NO2, ppb0.99632 (0.98475 - 1.00802)0.5361.00356 (0.97831 - 1.02945)0.785
NOx, ppb0.99772 (0.99243 - 1.00304)0.4010.99774 (0.97792 - 1.01796)0.826
PM10, µg/m30.99996 (0.99845 - 1.0011146)0.9890.99947 (0.99772 - 1.00121)0.553
Women
CO, ppm0.96500 (0.799205 - 1.16651)0.7110.92309 (0.70315 - 1.21183)0.564
SO2, ppb1.00078 (0.9794024 - 1.022638)0.9431.00220 (0.96635 - 1.03938)0.906
O3, ppb1.00112 (0.99442 - 1.00787)0.7430.99979 (0.99046 - 1.00921)0.966
NO, ppb1.00128 (0.99280 - 1.00982)0.7680.99413 (0.97200 - 1.01676)0.608
NO2, ppb0.99385 (0.97696 - 1.011030.4810.98418 (0.94982 - 0.01979)0.379
NOx, ppb1.00093 (0.99348 - 1.00843)0.8061.00776 (0.98597 - 1.03003)0.488
PM10, µg/m30.9999715 (0.99801 - 1.00193)0.9771.00001 (0.99773 - 1.00230)0.987

Abbreviation: IRR, incidence rate ratio.

aStatistically significant.

Table 7. The Results of Negative Binomial Regression of the Impact of Air Pollutants on Overall Deaths in the Elderly (Men and Women) Caused by Diabetes (Ratio of Increased Daily Mortality for Every Unit Increase in Average Daily Emissions)
PollutantCrude IRR* and 95%CIP-ValueAdjusted IRR and 95%CIP-Value
Total
CO, ppm1.03085 (0.93750 - 1.33492)0.5300.97666 (0.83972 - 1.13592)0.759
SO2, ppb1.00602 (0.99180 - 1.02044)0.4081.00168 (0.98161 - 1.02215)0.871
O3, ppb1.99943 (0.99515 - 1.00373)0.7971.00021 (0.99441 - 1.00604)0.943
NO, ppb1.00263 (0.99781 - 1.00748)0.2841.00155 (0.99082 - 1.01239)0.778
NO2, ppb1.00168 (0.99198 - 1.01147)0.7351.00018 (0.9819871 - 1.01871)0.985
NOx, ppb1.00225 (0.99815 - 1.00636)0.2821.00213 (0.99178 - 1.01259)0.687
PM10, µg/m31.00015 (0.99891 - 1.00140)0.8071.00010 (0.99874 - 1.00146)0.880
Men
CO, ppm1.02578 (0.88247 - 1.19237)0.7400.99749 (0.79443 - 1.25246)0.983
SO2, ppb1.00263 (0.97543 - 1.03058)0.8510.99846 (0.96648 - 1.0315)0.926
O3, ppb0.99956 (0.99298 - 1.00618)0.8961.00048 (0.99133 - 1.00971)0.918
NO, ppb1.00379 (0.99633 - 1.01132)0.3201.00701 (0.98453 - 1.03001)0.544
NO2, ppb1.000005 (0.98478 - 1.01546)1.0001.00378 (0.96681 - 1.042165)0.844
NOx, ppb1.00225 (0.99590 - 1.00864)0.4880.997102 (0.97589 - 1.01878)0.792
PM10, µg/m30.99971 (0.99776 - 1.00166)0.7710.9996 (0.99752 - 1.00185)0.779
Women
CO, ppm1.00903 (0.89220 - 1.14116)0.8860.94555 (0.76995 - 1.16119)0.593
SO2, ppb1.00594 (0.98900 - 1.023182)0.4941.00001 (0.97416 - 1.02654)0.999
O3, ppb1.00005 (0.99448 - 1.00566)0.9840.99960 (0.99208 - 1.00717)0.918
NO, ppb1.000452 (0.994045 - 1.0069)0.8901.001361 (0.98887 - 1.01400)0.832
NO2, ppb1.00195 (0.98942 - 1.01463)0.7611.00222 (0.98053 - 1.02437)0.842
NOx, ppb1.00069 (0.99525 - 1.00615)0.8041.00145 (0.98931 - 1.01374)0.815
PM10, µg/m31.00004 (0.99842 - 1.00166)0.9581.00007 (0.99832 - 1.00182)0.934

Abbreviation: IRR, incidence rate ratio.

aStatistically significant.

Table 8. The Results of Negative Binomial Regression of the Impact of Air Pollutants on Overall Daily Deaths in the Elderly (Men and Women) Caused by Other Diseases (Ratio of Increased Daily Mortality for Every Unit Increase in Average Daily Emissions)
PollutantCrude IRR and 95%CIP-ValueAdjusted IRR and 95%CIP-Value
Total
CO, ppm0.92516 (0.87798 - 0.97488)0.004a0.90067 (0.83224 - 0.97473)0.009a
SO2, ppb1.00602 (0.99180 - 1.02044)0.4991.00401 (0.99366 - 1.014469)0.499
O3, ppb1.00373 (1.00156 - 1.00591)0.001a1.00361 (1.00064 - 1.00658)0.017a
NO, ppb1.00263 (1.00006 - 1.00521)0.048a1.00257 (0.99664 - 1.00852)0.396
NO2, ppb0.99281 (0.98772 – 0.99793)0.006a0.99813 (0.98852 - 1.00783)0.705
NOx, ppb1.00225 (0.99815 - 1.00636)0.6461.00232 (0.99646 - 1.00821)0.438
PM10, µg/m31.00015 (0.99891 - 1.00140)0.3001.00011 (0.99935 - 1.00087)0.769
Men
CO, ppm0.95237 (0.89012 - 1.01897)0.1570.96411 (0.86908 - 1.06953)0.490
SO2, ppb1.00280 (0.99266 - 1.011224)0.6881.00592 (0.99229 - 1.01973)0.396
O3, ppb1.00280 (0.99986 - 1.00575)0.0611.00243 (0.99840 - 1.00646)0.237
NO, ppb1.00147 (0.99805 - 1.00490)0.3991.00295 (0.99420 - 1.01178)0.509
NO2, ppb0.99439 (0.98767 - 1.00116)0.1050.99895 (0.98548 - 1.01261)0.880
NOx, ppb0.99969 (0.99673 - 1.00267)0.8420.99833 (0.98963 - 1.00711)0.709
PM10, µg/m30.99954 (0.99861 - 1.000460.3290.99969 (0.99868 - 1.00071)0.558
Women
CO, ppm0.944729 (0.87199 - 1.02353)0.1640.95721 (0.84999 - 1.07796)0.471
SO2, ppb0.99669 (0.98410 - 1.00944)0.6090.99577 (0.97993 - 1.01187)0.605
O3, ppb1.00391 (1.00061 - 1.00722)0.020a1.00446 (0.99996 - 1.00898)0.052
NO, ppb1.00002 (0.99617 - 1.00387)0.9910.99952 (0.99094–1.00818)0.914
NO2, ppb0.99469 (0.98700 - 1.00245)0.1800.99727 (0.98320 - 1.01154)0.707
NOx, ppb0.99934 (0.99600 - 1.00270)0.7031.00331 (0.99492 - 1.01177)0.440
PM10, µg/m30.99993 (0.99889 - 1.00096)0.8971.00061 (0.99949 - 1.00174)0.281

Abbreviation: IRR, incidence rate ratio.

aStatistically significant.

The results of multivariate analysis indicated that CO was directly related to cardiovascular death of the elderly, but this relation disappeared in the gender subgroups, probably because the population size decreased (Table 4). Air pollutants did not show any significant effect on respiratory- (Table 5), trauma- (Table 6), and diabetes- (Table 7) related deaths in the elderly of Kerman city. The results of multivariate analysis of air pollutants indicated that ozone played a significant role in increasing the death of the elderly who died from other diseases (Table 8).

5. Discussion

This study aimed to investigate the relation between air pollutants and the number of elderly deaths in one of the major Iranian cities. The results indicated that CO played a significant role in the cardiovascular deaths of the elderly. Indeed, CO triggers complex pro-inflammatory phenomena in the airways and combines with blood hemoglobin, and forms a stable hybrid, which is carboxyhemoglobin, thereby causing hypoxia and heart failure. Moreover, it affects the central nervous system and eventually, can lead to death (11). Studies conducted in Taiwan also showed a relation between CO and cardiac mortality, especially in the elderly and in the winter (12). Another study conducted on British individuals aged over 45 years, also found a significant relation between CO and cardiovascular deaths (13). In Tehran, studies found that the most important effect of CO was on the cardiovascular system and increase in cardiovascular deaths (14), and there was a significant relation between CO and the daily number of deaths among people aged over 64 years in Tehran (15). The present study also showed that CO could probably affect deaths among the elderly. However, we found no significant relation between CO and deaths caused by respiratory diseases, trauma, or diabetes in the elderly.

In this study, there was a relation between NO and total deaths in the elderly, especially women. However, the results of this study did not show a significant impact of nitrogen oxides on deaths caused by cardiovascular diseases, respiratory diseases, trauma, diabetes, or other diseases in the elderly. The results of a study on people aged 50 - 64 years in Denmark showed no significant relation between nitrogen dioxide (NO2) and deaths caused by cardiac diseases, including myocardial infarction, angina pectoris, high blood pressure, and stroke and diabetes (16). However, the results of a study from Canada on people with an average age of 60 indicated a relation between all causes of death and NO2 (17). Wong in China also showed a relation between NO2 and deaths caused by cardiac diseases among hospital-admitted patients (18). Given the aforementioned controversies and inconsistencies, it seems that NO2 and its association with mortality require further investigation.

The results of this study showed that SO2 did not have a significant impact on deaths caused by respiratory diseases, trauma, and diabetes, as well as other diseases in the elderly. However, there was a significant relation between SO2 and all deaths among elderly women. Interestingly, the aforementioned issue was not seen in elderly men. In a study conducted in Kerman, Iran increased SO2 was significantly related to respiratory deaths in men (19) and was also associated with increased respiratory hospital admissions among women (20). However, in a study conducted in Beijing long-term exposure to SO2 was not related to respiratory deaths (21). Similarly, in another study from Taiwan, there was no relation between SO2 and respiratory deaths (12), and in Spain, there was no relation between SO2 concentration and patients admitted to hospitals due to asthma attacks (22) either. This lack of relation was also reported in another study conducted in New York (23).

In the present study, there was a significant relation between ozone and total deaths in elderly women as well as total deaths caused by other diseases. However, the results of multivariate analysis indicated that ozone did not significantly correlate with elderly deaths caused by cardiovascular and respiratory diseases as well as trauma and diabetes. Another study from China indicated that there was no significant relation between ozone and deaths caused by respiratory diseases (18) either. Also, ozone concentration was not related to asthma attacks in Spain (22). In contrast, ozone was related to respiratory deaths in men in Kerman (24).

Apparently, PM10 did not increase the death of elderly people in Kerman, Therefore, more research should be conducted in this regard. Several mechanisms have been proposed about how PM may impact death, including pneumonia, exacerbation of atherosclerosis, changes in heart function, inflammation of the air sacs, aggravation of lung diseases, increased blood clotting, increased blood viscosity, increased plasma fibrinogen, and changes in heartbeat (25).

However, it seems that further studies are still needed to determine the mechanism of its action. Inhalation of PM can cause oxidative stress and inflammatory responses in the lungs (26). Also, PM can penetrate into the lungs in the form of dust. Besides, they may pass through the lungs and enter blood circulation and reach other organs (27). In studies conducted in Taiwan, increased systolic and diastolic blood pressure was associated with increased annual average levels of PM2.5 and PM10 (28). In another study conducted in China, a relation was seen between PM10 and the number of overall deaths, and the impact was more severe on people aged 45 to 65 years than younger people (25). Conversely, another study conducted in Taiwan found no significant relation between PM10 and respiratory deaths (12). Furthermore, a significant relation was seen between short-term changes in deaths and PM10 and PM2.5 in several US cities (29). In a previous study in Kerman, PM10 significantly increased respiratory mortality among men (24).

Epidemiological studies conducted over the past two decades around the world have shown that the effects of air pollution on human health and deaths associated with air pollution are on the rise (30).

Kerman City encounters sand storms in the spring and autumn (31). Also, several stone, sand, and gravel crushing plants, as well as asphalt plants, operate around the city, which contribute to this city’s air pollution. Therefore, it seems essential to pay particular attention to vulnerable groups, particularly the elderly on days with high air pollution. Suitable planning such as reducing elders’ commuting time on high air pollution days can help prevent mortality. Table 9 presents the results of several studies conducted in various regions around the world about the effect of air pollution on mortality in the elderly. Similar to the findings of our study, some other studies also suggest that air pollution can contribute to increased cardiovascular and respiratory mortality in the elderly.

Table 9. A Summary of Studies Conducted in Various Regions Around the World on the Effect of Air Pollution on Mortality in the Elderly
IDYearCountry/RegionResults
Fischer et al. (32)2003NetherlandsThe study showed that the pollutants PM10, BS, and SO2, NO2 and CO increase the risk of mortality, especially in the elderly (individuals with 65 - 74 and higher than or equal to75 years of age).
Daumas et al. (33)2004BrazilThe study showed that an increase in total suspended particles (TSP) levels from the 10th to the 90th percentile (104.7 µg/m3) increase the risk for mortality in elderly people from cardiovascular and respiratory diseases.
Filleul et al. (34)2004BordeauxThe study showed that an increase of 10 mug/m3 of black smoke increased the risk of cardiorespiratory mortality among the elderly (odds ratio = 1.30, 95% CI: 1.01 - 1.68).
Enstrom (35) 2005CaliforniaThe study showed that for the initial period, 1973 - 1982, a 10-mu g/m3 increase in PM2.5 increased risk of mortality in the elderly RR (1.04, 1.01 - 1.07). However, this risk was no longer present for the subsequent period, 1983 - 2002. The findings presents no current relation between fine particulate pollution and total mortality in elderly Californians, but they do not rule out a small effect, particularly before 1983.
Cakmak et al. (36)2007ChileThe study shows that for elderly above the age of 85 years, the percentage increases in non - accidental mortality associated with an increase in PM10 equivalent to its mean was 14.03 (3.87), for O3 8.56 (2.02), for SO2 7.92 (3.23); and for CO 8.58 (4.45). Results suggested that the very elderly are particularly vulnerable to dying from air pollution.
Halonen et al. (37)2009FinlandThe study indicated an association of hospital admissions for arrhythmia with Aitken mode particles and PM2.5 from traffic. There were also positive associations between most particle fractions with admissions for pneumonia and asthma - chronic obstructive pulmonary disease (COPD). All particle fractions namely Aitken, accumulation, and coarse mode caused adverse respiratory health effects in the elderly. Generally, associations were stronger for respiratory compared to cardiovascular consequences.
Jimenez et al. (38)2011Madrid (Spain)The study indicated that in the elderly coarser PM fractions (PM10 and PM10-2.5) is associated with respiratory - specific mortality, and PM2.5 is related to cardiovascular - specific mortality. In addition, compared to winter, the risk of mortality due to exposure to particulate matter was greater in summer.
Krstic (39)2011VancouverFindings showed a very weak negative association between air pollution and the elderly’s mortality.
Goldberg et al. (8)2013Montreal, QuebecThe study found that daily non-accidental mortality among the elderly is positively associated with all air pollutants except ozone, especially amongst elderly persons having cardiovascular diseases, congestive heart failure, and diabetes. It was also suggested that individuals with certain health conditions, especially those with diabetes and cardiovascular diseases, hypertension, atrial fibrillation, and cancer, might be vulnerable to the short-term effects of air pollution.
Vanos et al. (40)2013CanadaThe study revealed that weather type had the greatest modifying effect on the risk of dying due to ozone in the entire elderly population. This effect was the highest on average for the dry tropical (DT) weather type. All-weather type risk estimates increased with age due to exposure to carbon monoxide (CO), nitrogen dioxide (NO2), and Sulphur dioxide (SO2). For all weather types increased levels of air pollution were found to have adverse health effects for elderly individuals. Air pollution on the hot dry (DT) and hot humid (MT) days had negatively affected the entire population.
Yang et al. (6)2018Hong KongThe study revealed that long - term exposure to ambient PM2.5 and black carbon (BC) caused an elevated risk of cardiovascular mortality in elderly with the age of equal and greater than 65.
Yap et al. (7) 2019SingaporeThe study indicated that in single - day lag models, every 10 µg/m3 rise in particulate matter increases non - accidental and cardiovascular mortality in the elderly. This was significant in the elderly ≥ 65 years and were seen in the acute phase of lag 0 - 5 days.
Dalecka et al. (41)2021GermanyThe study revealed that after adjusting for reduced lung function and additional covariates, long - term exposures to NOx and NO2 were associated with increased risks of cardio - pulmonary mortality (CPM) among elderly women. The mediation analysis showed significant indirect effects of NO2 and NOx on CPM mediated through reduced FEV1 and FVC. The largest indirect effects were found for exposures to NO2 and NOx mediated through reduced FVC.

5.1. Conclusions

It seems among the elderly, cardiovascular diseases are more vulnerable to air pollution than others. Carbon monoxide, nitrogen oxide, and sulfur dioxide may play an important role in elderly deaths. A warning system to reduce elders’ commuting on high air pollution days is suggested.

Acknowledgements

Footnotes

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