Original Article
Desert Dust Is a Risk Factor for the Incidence of Acute
Myocardial Infarction in Western Japan
Ryuichi Matsukawa, MD, PhD; Takehiro Michikawa, MD, PhD; Kayo Ueda, MD, PhD;
Hiroshi Nitta, PhD; Tomohiro Kawasaki, MD, PhD; Hideki Tashiro, MD, PhD;
Masahiro Mohri, MD, PhD; Yusuke Yamamoto, MD, PhD
Downloaded from http://circoutcomes.ahajournals.org/ by guest on June 17, 2017
Background—Recently, there has been increasing concern about adverse health effects of exposure to desert dust events.
However, the association between dust and the incidence of ischemic heart diseases is unknown. The aim of the present
study was to elucidate whether Asian dust (AD), a windblown sand dust originating from mineral soil in China and
Mongolia, is associated with the incidence of acute myocardial infarction (AMI).
Methods and Results—We investigated the data regarding hospitalization because of AMI among 3068 consecutive patients
from 4 AMI centers in Fukuoka, Japan, and data for AD from April 2003 to December 2010. We applied a time-stratified
case-crossover design to examine the association between AD and the incidence of AMI. Using a conditional logistic
regression analysis, we estimated the odds ratios of AMI associated with AD after controlling for ambient temperature
and relative humidity. The occurrence of AD events 0 to 4 days before the day of admission was significantly associated
with the incidence of AMI. In particular, the occurrence of AD 4 days before admission was significantly associated with
the onset of AMI.
Conclusions—These data suggest that exposure to AD a few days before symptom onset is associated with the incidence of
AMI. (Circ Cardiovasc Qual Outcomes. 2014;7:00-00.)
Key Words: air pollution ◼ dust ◼ myocardial infarction
R
ecently, there has been increasing concern about adverse
health effects of exposure to desert dust events, natural
phenomenon in which a windblown sand dust originating
from the mineral soil of deserts transported to downwind
areas. Desert dust clouds carry not only coarse particles but
also fine particles and various chemical components from
anthropogenic sources1 during its long-range transport.
Exposure to elevated level of fine particles is known to
trigger ischemic heart diseases.2 However, studies examining
the association between coarse particles and cardiovascular
diseases are inconsistent.3,4 Recent studies focusing on desert dust events suggested that coarse particles had stronger
effects on mortality during Saharan dust days than those during non-Saharan dust days.5,6 Especially, Pérez et al7 showed
that Saharan dust was associated with cardiovascular mortality. However, we are unaware of studies that examined
whether exposure to desert dust triggers acute myocardial
infarction (AMI).
Fukuoka prefecture is located in Western Japan and is
nearest to the Asian continent (Figure 1A); thus, it often
experiences Asian dust (AD) events, a windblown sand
dust originating from mineral soil in China and Mongolia.
Recently, it has been reported that AD exposure is associated
with the risk of asthma8 and atherothrombotic brain infarction9
in Japan. It is suggested that AD clouds carry not only desert
dust but also microorganisms, chemical components, and gaseous pollutants. AD has become an object of public concern
in Japan with respect to preventing respiratory and cardiovascular diseases. However, it remains unknown whether AD is
associated with the risk of coronary heart disease. We focused
on the association between AD events and the incidence of
AMI, particularly in patients with coronary heart diseases.
In the present study, we used a time-stratified case-crossover
design to elucidate the association between AD and the incidence of AMI.
Methods
Patient Data
Patient data were retrospectively collected from the 4 hospitals in
Fukuoka prefecture, including Saiseikai Fukuoka General Hospital in
Fukuoka city, JCHO Kyushu Hospital in Kitakyushu city, St. Mary’s
Hospital, and Shin-Koga Hospital in Kurume city (Figure 1). This
study included data for patients aged ≥20 years with AMI admitted to
the 4 participating hospitals within 24 hours of onset between April
Received February 5, 2014; accepted June 25, 2014.
From the Division of Cardiology, Cardiovascular and Aortic center of Saiseikai Fukuoka General Hospital, Fukuoka, Japan (R.M., Y.Y.); Center for
Environmental Health Sciences, National Institute for Environmental Studies, Tsukuba, Japan (T.M., K.U., H.N.); Department of Cardiology, Shin-Koga
Hospital, Fukuoka, Japan (T.K.); Division of Cardiology, St. Mary’s Hospital, Fukuoka, Japan (H.T.); and Department of Cardiology, Japan Community
Healthcare Organization (JCHO), Kyushu Hospital, Fukuoka, Japan (M.M.).
The Data Supplement is available at http://circoutcomes.ahajournals.org/lookup/suppl/doi:10.1161/CIRCOUTCOMES.114.000921/-/DC1.
Correspondence to Ryuichi Matsukawa, MD, PhD, Division of Cardiology, Cardiovascular and Aortic center of Saiseikai Fukuoka General Hospital,
1-3-46 Tenjin Chuou-ku, Fukuoka 810-0001, Japan. E-mail [email protected]
© 2014 American Heart Association, Inc.
Circ Cardiovasc Qual Outcomes is available at http://circoutcomes.ahajournals.org
1
DOI: 10.1161/CIRCOUTCOMES.114.000921
2 Circ Cardiovasc Qual Outcomes September 2014
WHAT IS KNOWN
• Exposure to elevated levels of fine particulate matter
is known to be associated with ischemic heart disease morbidity and mortality.
• The association between desert dust particles
and cardiovascular diseases, however, has been
inconsistent.
WHAT THE STUDY ADDS
Downloaded from http://circoutcomes.ahajournals.org/ by guest on June 17, 2017
• We investigated the association between Asian
dust, a windblown sand dust originating from mineral soil in China and Mongolia and the incidence
of AMI.
• We found an increased risk of myocardial infarction
within 4 days after an Asian dust event (based on a
visibility standard), even after adjusting for humidity, temperature, small particulate matter, and other
copollutants.
2003 and December 2010. We included patients with a final diagnosis of ST-segment–elevation MI and non–ST-segment–elevation MI. The diagnosis of AMI (both ST-segment–elevation MI
and non–ST-segment–elevation MI) was determined according
to the universal definition of MI proposed by the Joint European
Society of Cardiology(ESC)/American College of Cardiology
Foundation(ACCF)/American Heart Association(AHA)/World Heart
Federation(WHF) Task Force.10 The study was approved by the institutional review board at each participating hospitals.
AD and Meteorologic Data
Data for ground-level observations of AD events and meteorologic
variables were measured at the Fukuoka local meteorologic observatory. The occurrence of an AD event was generally determined
according to a visibility-based observation at the same observatory
(http://www.jma.go.jp/en/kosa/). An AD event is reported when the
visibility reduces to <10 km. The daily mean ambient temperature
and relative humidity were calculated using hourly measurements.
Air Pollutant Data
Data for air pollutants were obtained from the atmospheric environmental database of the National Institute for Environmental
Studies. Air pollutants included suspended particulate matter
(SPM), photochemical oxidants, defined as a mixture of ozone and
other secondary oxidants generated by photochemical reactions,
nitrogen dioxide (NO2), and sulfur dioxide (SO2). SPM monitored
in Japan is theoretically assumed to be particles with a diameter of
<7 μm and is characterized by smaller size distribution than particulate matter <10 μm in aerodynamic diameter (PM10). There are 8
monitoring stations in Fukuoka city, 14 in Kitakyushu city, and 4 in
Kurume city. Therefore, we averaged the daily values and assigned
the citywide means of SPM, NO2, and SO2 and the 8-hour moving
average concentrations of photochemical oxidants to the patients
who admitted to the hospital located in the corresponding city.
Statistical Analysis
A time-stratified case-crossover design11 was applied to examine
the association between exposure to AD events and the risk of
hospitalization for AMI. Within-subject comparisons were made
between a case period and control periods. A case period was defined as the day of hospitalization. As control periods, we selected
the corresponding days of the week in the same month of the same
year as the case period. This control selection strategy is expected
to adjust for time-invariant covariates such as long-term trend,
seasonality by design.12 For example, if a hospitalization because
of AMI occurred on May 20, 3 control days were selected: May 6,
13, and 27. We used a conditional logistic regression model and
estimated the odds ratios (ORs) and 95% confidence intervals of
hospitalization associated with AD events after adjustment for the
4-day average ambient temperature and relative humidity from the
case day to 3 days prior. Because the effects of AD events were assumed to persist over the course of a few days, we used AD events
occurring on the case day (day 0) up to a few days earlier, and
examined single lag effect (days 0–5) and cumulative lag effect
(day 0–1, to days 0–5). In addition, SPM, photochemical oxidants,
NO2, and SO2 were added in the basic model to adjust for the effects of copollutants.
The visibility-based observation of AD events does not have information on the amount of the dust particles. According to the previous
study,13 it is possible that the association is more obvious with AD
events with higher particle level than those with lower particle level.
Hence, we also performed the same conditional logistic regression
analysis using heavy AD events (AD events with an SPM concentration of ≥50 μg/m3 [median value]), taking into consideration the
amount of coarse particles in AD. In addition, to examine the effect
modification, we performed stratified analyses according to age strata
(<65 and ≥65 years) and sex. We checked for statistical interactions
using cross-product terms of age strata or sex with AD events. All
analyses were performed using the STATA 11 software package
(StataCorp LP, College Station, TX).
Results
Patient Characteristics and Air Pollutant
Concentrations
There were 3068 patients with AMI in this study. A total
of 1954 patients (63.7%) were aged >65 years, and 879
patients (28.7%) were women. There were 75 days in the
study period when an AD event was observed, and most of
the AD events were observed from March to May (AD days;
Figure 2). A summary of the statistics of the air pollutants
on days with and without AD events is shown in Table 1.
The concentrations of pollutants excluding NO2 tended to
be higher on the days with AD events than on those without
AD events.
AD and the Incidence of AMI
The occurrence of AD 4 days before admission (day 4) was
significantly associated with the incidence of AMI (Figure 3A; OR, 1.33; 95% confidence interval, 1.05–1.69). We
also examined the association for cumulative lags. The occurrence of AD events at days 0 to 4 was significantly associated with the incidence of AMI (Figure 3B; OR, 1.20; 95%
confidence interval, 1.02–1.40). Because most of AD events
occurred in March to May, we repeated the analysis using
the data limited to this season (Table in the Data Supplement). The association and its lag pattern were similar to that
observed using year-round data. From these results, further
analyses focused on the association between AD and AMI
at day 4 and days 0 to 4. Although we further adjusted for
each air pollutant individually or all the pollutants simultaneously, the positive associations between the occurrence of
AD on days 0 to 4 and day 4 and the risk of AMI remained
(Table 2). When we examined the relationship between heavy
AD events, defined by the SPM concentration, and the risk
Matsukawa et al Desert Dust and AMI 3
A
B
Fukuoka City
Kitakyushu City
Figure 1. Maps of Japan and the Asian
Continent (A) and Fukuoka prefecture
(B). A, Fukuoka is located in Western
Japan and is the city nearest to the Asian
Continent. B, Four hospitals and monitoring
stations in Fukuoka prefecture participated
in this study.
Kurume City
Monitoring station
Hospital
30 mile
Meteorological observatory
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of AMI, a similar association was found between the onset of
AMI and the occurrence of heavy AD events (OR at day 4,
1.43 [95% confidence interval, 1.03–1.98]; OR at days 0–4,
1.21 [0.99–1.46]). The association between AD and the incidence of AMI on days 0 to 4 did not differ according to the
age strata or sex (Table 3).
Discussion
The findings of the present case-crossover study suggested
that AD is a potential trigger of AMI. Few studies have
investigated whether short-term exposure to desert dust is
associated with the cardiovascular morbidity.9 Recently,
Kamouchi et al9 showed that AD is associated with the frequency of atherothrombotic brain infarction but not other
types of ischemic stroke. The mechanisms underlying the
occurrence of both atherothrombotic brain infarction and
AMI are considered to be similar. The common background
between these diseases is thrombus formation attributable to
atherosclerotic plaque.
The mechanisms by which exposure to AD increases the
incidence of AMI are unknown. The levels of air pollutants,
including both particulate and gaseous pollutants, excluding NO2 were increased during AD events compared with
those measured in the periods without AD events (Table 1).
We observed that heavy AD events, defined by the SPM
(days)
18
The days observed Asian dust in Fukuoka
Full year
16
March-May
14
12
10
8
6
4
2
0
2003
2004
2005
2006
2007
2008
2009
2010
(year)
Figure 2. Number of days on which Asian dust events were
observed from 2003 to 2010.
concentration, were also associated with the risk of AMI
hospitalization. It has been reported that fine PM and SO2
and NOx from coal-fired power plant were associated with
cardiovascular risk.14,15 Furthermore, it has also been said
that smaller particles could have greater risk for cardiovascular disease.16 We observed the association of AD events
on AMI hospitalization. However, we cannot identify culprit
elements of AD for cardiovascular risk. We speculate that
AD may have more adverse health effects because of the
contaminated with finer particles and anthropogenic chemicals when AD passed through heavily industrial areas with
coal-fired power plants.
Previous animal and human studies have led to some
hypotheses regarding the mechanisms underlying the
adverse cardiovascular effects of short-term particulate
matter exposure.17 These studies suggest that inhaled particles induce systemic oxidative stress,18 inflammation,19,20
autonomic dysfunction, including tachycardia, reductions
in heart rate variability and hypertension,18,20–22 and hypercoagulability.23,24 Therefore, the particulate matter contained
in AD may stimulate plaque rupture according to these
mechanisms, resulting in AMI. Another possibility is that
unidentified substances are also involved in AD. A previous
study demonstrated that microbial components adhering to
AD induce allergic lung inflammation.25 Therefore, a systemic response to these adhered unknown microorganisms
originating from the distant desert may accelerate inflammation and thrombosis. Further studies are needed to clarify the
underlying mechanisms.
AD events contribute to a sharp increase in coarse particles
in Japan.1 Several studies have shown that elevated concentration of fine particulate matter is associated with hospitalization attributable to ischemic heart disease.24 On the contrary,
the association between coarse particles and cardiovascular
risk is less studied and the results are inconsistent. Peters et
al24 observed a positive but insignificant association between
coarse particles and AMI. Peng et al3 found no significant
association between coarse particles and hospital admissions for cardiovascular diseases after adjustment particulate matter <2.5 μm in aerodynamic diameter (PM2.5). Host
et al4 examined the association between coarse particle and
4 Circ Cardiovasc Qual Outcomes September 2014
Table 1. Levels of Air Pollutant on Days With AD Events and Non-AD Days (April 2003 to December 2010)
Pollutant
City
Days
Mean
SD
Minimum
25th
Percentile
50th
Percentile
75th
Percentile
Maximum
P Value*
31.9
21.5
38.4
48.6
66.2
170.0
<0.01
14.3
6.6
19.4
26.3
36.8
105.7
SPM, μg/m3
Fukuoka
AD days
Non-AD days
75
2757
58.1
29,7
Kitakyushu
AD days
Non-AD days
75
52.6
29.8
14.8
34.2
45.8
59.1
154.9
2757
25.4
13.9
5.0
15.2
22.2
32.1
114.6
<0.01
Kurume
AD days
Non-AD days
75
55.4
27.5
21.3
40.1
49.2
55.8
148.7
2754
32.6
14.8
2.9
22.2
30.0
39.8
107.2
<0.01
Ox, ppb
Fukuoka
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AD days
Non-AD days
75
56.6
13.2
13.6
48.2
58.2
65.8
88.9
2757
43.3
15.2
4.5
33.4
41.5
52.5
123.0
<0.01
Kitakyushu
AD days
Non-AD days
75
57.3
16.8
14.8
55.4
55.4
65.6
115.9
2757
40.2
14.6
5.7
30.4
39.0
49.1
127.9
<0.01
Kurume
AD days
Non-AD days
75
54.1
15.0
17.6
52.4
54.3
65.8
90.6
2757
41.8
16.5
5.5
29.9
39.5
52.2
99.0
<0.01
NO2, ppb
Fukuoka
AD days
Non-AD days
75
14.5
6.3
5.0
9.3
13.1
18.5
31.6
2757
14.7
6.8
1.9
9.6
13.5
18.9
51.9
0.72
Kitakyushu
AD days
Non-AD days
75
18.2
8.6
6.7
12.2
15.6
22.8
45.3
2757
18.8
7.3
2.4
13.3
18.0
23.5
53.8
75
15.6
5.4
6.1
12.0
15.4
19.2
33.3
2757
15.4
6.0
1.8
10.9
14.9
19.4
37.6
75
4.5
1.7
1.5
3.2
4.4
5.7
8.4
2757
3.7
1.6
0.7
2.5
3.5
4.6
12.8
0.43
Kurume
AD days
Non-AD days
0.75
SO2, ppb
Fukuoka
AD days
Non-AD days
<0.01
Kitakyushu
AD days
Non-AD days
75
4.4
1.9
1.3
2.9
4.2
5.5
9.8
2757
3.6
1.7
0.5
2.4
3.3
4.4
13.5
75
4.1
1.5
1.3
2.6
4.3
4.3
7.6
2756
3.9
2.0
0.4
2.2
3.7
5.2
15.8
<0.01
Kurume
AD days
Non-AD days
0.36
AD indicates Asian dust; Ox, photochemical oxidants; ppb, parts per billion; and SPM, suspended particulate matter.
*P values for the difference of concentrations of each pollutant between AD days and non-AD days were determined by Student t test.
cardiorespiratory hospitalization and observed significant
positive association only with those attributable to ischemic
heart disease for the elderly. AD particles may be modified
by chemical components from anthropogenic sources1 during its long-range transport. Further studies should focus on
health effects of different size distribution and various chemical characterization of AD.
There are some limitations associated with the present
study. Limited number of cases and AD days could have
resulted in limited statistical power. Especially, we examined
the association during the potential lags. Therefore, observed
association could be observed by chance. Further study with
larger sample size would be necessary. No detailed information was available regarding patient behavior, the degree of
Matsukawa et al Desert Dust and AMI 5
Table 3. Association Between Asian Dust and the Incidence
of Acute Myocardial Infarction on Day 4 or Days 0 to 4
According to the Age Strata and Sex
Association between AD and the incidence of AMI
A
B
Single lag
Cumulative lag
Day0
Day0-1
Day1
Day0-2
Day2
0.5
1
1.5
Day4
Day0-4
≥65 (1954 cases)
1.36
1.00–1.85
Day5
Day0-5
Men (2189 cases)
1.36
1.02–1.81
Women (879 cases)
1.28
0.82–1.98
<65
1.09
0.83–1.43
≥65
1.25
1.02–1.53
Men
1.17
0.96–1.42
Women
1.25
0.93–1.67
2
0.5
1
1.5
Sex
0.25
Days 0–4
95% CI
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Table 2. Association Between Asian Dust and the Incidence
of Acute Myocardial Infarction After Adjustment by
Copollutant
Age, y
0.40
Sex
0.57
CI indicates confidence interval; and OR, odds ratio.
*Adjusted for 4-day averaged ambient temperature and relative humidity
from lag 0 to lag 3.
events according to the SPM concentration, further studies
of AD events based on quantitative measurements (eg, the
Light Detection and Ranging system)26 are needed.
In conclusion, we observed an association between AD
events and the occurrence of AMI. Exposure to AD may be a
trigger of AMI.
Adjusted
OR
95% CI
Meteorologic
variables*
1.33
1.04–1.69
Sources of Funding
Meteorologic
variables and SPM
1.32
1.05–1.68
This study was supported by Grants-in-Aid for Scientific Research
(24310024) from the Japan Society for the Promotion of Science
(Tokyo, Japan).
Meteorologic
variables and Ox
1.32
1.04–1.68
Meteorologic
variables and NO2
1.32
1.04–1.68
Meteorologic
variables and SO2
1.32
1.04–1.68
Meteorologic variables
and SPM, Ox, NO2, SO2
1.31
1.03–1.67
Meteorologic
variables*
1.19
1.02–1.40
Meteorologic
variables and SPM
1.20
1.02–1.41
Meteorologic
variables and Ox
1.19
1.01–1.39
Meteorologic
variables and NO2
1.19
1.01–1.40
Meteorologic
variables and SO2
1.19
1.01–1.40
Meteorologic variables
and SPM, Ox, NO2, SO2
1.19
1.01–1.40
Covariates
Adjusted
for
Age, y
0.87–1.87
individual exposure to AD and other air pollutants, or coronary risk factors, such as hypertension, dyslipidemia, and
diabetes mellitus. In addition, the data for AD events provided by the Japan Meteorological Agency were dependent
on the distance of visibility. Although we defined heavy AD
Days 0–4
0.77
Day 4
1.26
Figure 3. Odds ratios with 95% confidence intervals (CIs) of
acute myocardial infarction (AMI) on Asian dust (AD) days
compared with non-AD days for each single lag (A) and
cumulative lag (B), adjusted for ambient temperature and
relative humidity.
Adjusted
for
Pinteraction
<65 (1114 cases)
95% CI
Day 4
95% CI
Day0-3
Day3
0
Adjusted OR*
CI indicates confidence interval; OR, odds ratio; Ox, photochemical oxidants;
and SPM, suspended particulate matter.
*Adjusted for 4-day averaged ambient temperature and relative humidity
from lag 0 to lag 3.
Disclosures
None.
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Desert Dust Is a Risk Factor for the Incidence of Acute Myocardial Infarction in Western
Japan
Ryuichi Matsukawa, Takehiro Michikawa, Kayo Ueda, Hiroshi Nitta, Tomohiro Kawasaki,
Hideki Tashiro, Masahiro Mohri and Yusuke Yamamoto
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Matsukawa et al.
Desert dust and AMI
SUPPLEMENTAL MATERIAL
Supplemental Table Association between Asian dust (AD) and the incidence of acute myocardial infarction (95% CI) during
March to May (794 cases)
Lag
Adjusted OR*
95% CI
Day0
1.19
0.89-1.59
Day1
Day2
Day3
Day4
Day5
1.07
0.99
1.22
1.23
0.99
0.80-1.44
0.74-1.31
0.93-1.61
0.92-1.65
0.73-1.35
Day0-1
Day0-2
Day0-3
Day0-4
Day0-5
1.11
1.08
1.14
1.20
1.14
0.87-1.42
0.86-1.34
0.93-1.40
0.99-1.47
0.94-1.38
OR: odds ratio; CI: confidence interval
*Adjusted for 4-day averaged ambient temperature and relative humidity from lag0 to lag3