(Stroke. 1997;28:1717-1723.)
© 1997 American Heart Association, Inc.
Articles |
From the School of Public Health (H.-Y.C.), Taipei Medical College, Taipei; Graduate Institute of Epidemiology (W.-I.H., Y.-H.H., C.-J.C.), College of Public Health, National Taiwan University, Taipei; and Department of Neurology (C.-L.S., S.-F.C.), Lotung Poh-Ai Hospital, Ilan, Taiwan, ROC.
Correspondence to Prof Chien-Jen Chen, Graduate Institute of Epidemiology, College of Public Health, National Taiwan University, 1 Jen-Ai Road Section 1, Taipei 10018, Taiwan. E-mail cjchen{at}ha.mc.ntu.edu.tw
| Abstract |
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Methods A total of 8102 men and women from 3901 households were recruited in this study. The status of cerebrovascular disease of study subjects was identified through home-visit personal interviews and ascertained by review of hospital medical records according to the World Health Organization criteria. Information on consumption of well water, sociodemographic characteristics, cigarette smoking, and alcohol consumption habits, as well as personal and family history of diseases, was also obtained. Arsenic concentration in the well water of each household was determined by hydride generation and atomic absorption spectrometry. Logistic regression analysis was used to estimate multivariate-adjusted odds ratios and 95% confidence intervals for various risk factors of cerebrovascular disease.
Results A significant dose-response relationship was observed between arsenic concentration in well water and prevalence of cerebrovascular disease after adjustment for age, sex, hypertension, diabetes mellitus, cigarette smoking, and alcohol consumption. The biological gradient was even more prominent for cerebral infarction, showing multivariate-adjusted odds ratios of 1.0, 3.4, 4.5, and 6.9, respectively, for those who consumed well water with an arsenic content of 0, 0.1 to 50.0, 50.1 to 299.9, and >300 µg/L.
Conclusions Long-term exposure to inorganic arsenic from well water was associated with an increased prevalence of cerebrovascular disease, especially cerebral infarction.
Key Words: arsenic cerebrovascular disorders water pollution risk factors hypertension
| Introduction |
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350 000 people
may drink water containing more than this level of
arsenic.3 Arsenic has been well documented as one of the major risk factors for blackfoot disease (BFD), a unique peripheral vascular disease identified in the endemic area on the southwestern coast of Taiwan, where residents had used high-arsenic artesian well water for more than 50 years. Clinically, the disease starts with numbness or coldness and ends with gangrene and spontaneous amputation of one or more affected extremities.4 5 The pathological types of BFD include arteriosclerosis obliterans (70%) and thromboangiitis obliterans (30%), which develops from severe underlying systemic arteriosclerosis.6 An increased risk of peripheral vascular disease as a result of drinking water containing inorganic arsenic has also been observed in Mexico, Chile, and the Xinjiang province of China.7 8 9 The association between peripheral vascular lesions and chronic arsenic exposure through inhalation of airborne arsenic in copper smelter workers or consumption of contaminated wine in vintners in Moselle has also been described in previous studies.10 11
Both environmental and occupational exposure to inorganic arsenic have been shown to produce an increased but not statistically significant mortality from cerebrovascular disease (CVD). An excess mortality from CVD was associated with environmental exposure to inorganic arsenic through drinking water among BFD patients and residents of Taiwan.5 12 Occupational exposure to inorganic arsenic for workers in copper smelters and in pesticide manufacturing has also been related to increased mortality from CVD.13 14 15 However, most previous studies were either ecological correlation studies or occupational cohort studies. The former may have the problem of ecological fallacy, and the latter may be subject to the limitations of multiple exposure to various airborne chemicals and the healthy-worker effect, which may underestimate the arsenic-induced risk due to the fact that the severely ill are ordinarily excluded from employment. We performed this study to investigate the dose-response relationship between the prevalence of CVD and inorganic arsenic ingested through drinking well water among residents of Lanyang Basin in Taiwan.
| Materials and Methods |
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Names and addresses of all adult residents in the study area were abstracted from household records kept in local household-registration offices where sociodemographic characteristics including sex, birth date, marital status, education, migration, and occupation of all members of every household are registered and annually updated. The selection of study subjects from the household-registration system was effective and efficient because of the completeness and accuracy of the registration information. A total of 8102 residents, including 4056 men and 4046 women, who agreed to participate were interviewed at home from October 1991 through September 1994. The standardized personal interview based on a structured questionnaire was conducted by four public health nurses who were well trained in interview technique and questionnaire details. Information obtained from the interview included history of well-water consumption, residential history, sociodemographic characteristics, history of cigarette smoking, history of alcohol consumption, physical activities, history of sunlight exposure, and personal and family histories of hypertension, diabetes, CVD, heart disease, and cancer. The history of cigarette smoking that was obtained included age at which the subject started smoking, average number of cigarettes smoked per day, and age at which smoking was stopped. Information concerning the age at which habitual alcohol consumption was begun, average quantity of alcohol consumption per day, and age at which alcohol consumption was stopped was also obtained. Physical activity level at work was evaluated on the basis of the type of job and hours worked per day.
A detailed history of residential village water consumption, including
water source and duration of consumption, obtained from the
questionnaire interview was used to derive cumulative arsenic exposure
from drinking well water. A total of 3901 well-water samples (one
sample from each household) were collected during home interviews,
immediately acidified with hydrochloric acid, and then stored at
-20°C until subsequent assay. Hydride generation combined with flame
atomic absorption spectrometry was used to determine arsenic
concentration in these samples. The arsenic exposure level of each
study subject from drinking well water was derived from the arsenic
concentration in well water of the household. The cumulative arsenic
exposure from drinking well water in milligrams per liter times number
of years the water was consumed (mg/Lxyear) for each study
subject was calculated as the sum of products derived by
multiplying the arsenic concentration in well water (in milligrams per
liter) by the duration of drinking well water (in years) during
consecutive periods of living in different villages, ie,
(CixDi),
where Ci is the arsenic level in well water of the residence where a
given study subject lived during period i and Di is the duration of
drinking well water during the same period i. In other words, this
cumulative index equates the level of arsenic in well water with the
duration of drinking the water. Both cumulative arsenic exposure from
drinking well water and average arsenic concentration in drinking water
were available only for those subjects who had a complete history of
arsenic exposure from drinking well water throughout their lifetime.
For a given subject, these two arsenic exposure indices were classified
as unknown if the arsenic level in the well water of any residence
throughout the subject's lifetime was not available.
Cases of CVD were identified from home-visit personal interview and
ascertained by hospital medical records according to the World
Health Organization criteria.17 During the interview,
blood pressure was also measured according to the standard protocol
recommended by the World Health Organization. Both systolic and
diastolic blood pressures were measured three times with a
mercury sphygmomanometer after the subject had rested for 20 minutes or
longer. The average of these three measurements was used for
analysis. Diagnostic criteria for hypertension was
an average systolic blood pressure
160 mm Hg, an
average diastolic blood pressure
95 mm Hg, or a
history of hypertension regularly treated with antihypertensive drugs.
Diabetes mellitus patients were defined as those who had a history of
diabetes mellitus and were regularly treated with sulfonylurea or
insulin.
In the analysis of the association between indices of long-term inorganic arsenic exposure and CVD prevalence, age- and sex-adjusted odds ratios and their 95% confidence intervals (CIs) were derived from multiple logistic regression models.18 Logistic regression analyses were also used to estimate the multivariate-adjusted odds ratios and their 95% CIs.
| Results |
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70 years old,
respectively. A total of 3309 (40.9%) of subjects were illiterate,
4149 (51.3%) had an educational level of elementary school, and only
625 (7.7%) had an educational level of junior high school or above.
The subjects were mainly farmers or fishermen.
A total of 139 CVD patients, including 95 with cerebral infarction,
were identified and confirmed in this study. Table 1
shows age- and sex-specific prevalence
of CVD. CVD prevalence increased with age in both men and women. Men
had a higher CVD prevalence than women for all age groups except the
50- through 59-year-olds. The age-adjusted CVD prevalence was higher in
men than in women. The age-specific CVD prevalences by inorganic
arsenic level in well water are shown in Fig 2
. Subjects
50 years old who drank well
water with an arsenic concentration
300 µg/L had higher CVD
prevalences than those who drank water with arsenic levels of 50
through 299 and <50 µg/L, respectively.
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Table 2
shows no significant associations
between CVD prevalence and cigarette smoking or alcohol consumption.
The age- and sex-adjusted odds ratios of being affected with CVD for
those who had smoked cigarettes <40 and
40 years were 0.84 and 1.40,
respectively, compared with nonsmokers. Compared with subjects who had
no alcohol drinking habit, the age- and sex-adjusted odds ratios of
being affected with CVD were 1.46 and 1.47, respectively, for those who
had an alcohol drinking habit for <40 and
40 years.
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As shown in Table 3
, there were
significant dose-response relationships between CVD and cerebral
infarction prevalence and arsenic content in well water after
adjustment for age and sex. The prevalences of CVD and cerebral
infarction were found to increase significantly with cumulative arsenic
exposure from <0.1 to >5.0 mg/Lxyear. The biological gradient
between the prevalence of cerebral infarction and arsenic exposure
indices was much more prominent than that for CVD prevalence. Patients
affected with hypertension had a significantly higher prevalence of CVD
and cerebral infarction than nonhypertensive residents after adjustment
for age and sex; increased prevalences of CVD and cerebral infarction
were found for diabetic patients, but the association was significant
for CVD only.
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Table 4
shows
multivariate-adjusted odds ratios of being affected
with CVD and cerebral infarction for subjects with hypertension and
diabetes mellitus and provides arsenic exposure indices
analyzed by multiple logistic regression analysis. As
shown in each model I for analysis of CVD and cerebral
infarction prevalence, there were statistically significant
dose-response relationships between the prevalences of CVD and cerebral
infarction and arsenic content in well water after adjustment for
multiple risk factors. As also shown in each model II for CVD and
cerebral infarction prevalence, significant dose-response relationships
were observed between cumulative arsenic exposure and prevalence of CVD
and cerebral infarction after adjustment for age, sex, cigarette
smoking, alcohol consumption, hypertension, and diabetes mellitus.
Hypertensive patients still had a significantly higher prevalence of
CVD and cerebral infarction than nonhypertensive patients, but the
associations became statistically nonsignificant between the status of
diabetes mellitus and the prevalence of CVD and cerebral
infarction.
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| Discussion |
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Generally speaking, men had a higher mortality rate and a similar incidence of CVD compared with women in Taiwan. In the present study, men had a higher CVD prevalence than women, but the gender difference was not statistically significant after adjustment for age, arsenic exposure indices, hypertension, diabetes mellitus, cigarette smoking, and alcohol consumption. Cigarette smoking and alcohol consumption have been documented as risk factors for CVD.31 32 33 34 However, positive but statistically nonsignificant associations with CVD were observed for cigarette smoking and alcohol consumption in the present study.
Hypertension is a well-documented risk factor for CVD. As shown in the present study, hypertension was also associated with the prevalence of CVD and cerebral infarction after adjustment for age, sex, arsenic exposure indices, cigarette smoking, and alcohol consumption. This finding is similar to those reported in previous studies.35 36 37 Diabetes mellitus has also been reported as a CVD risk factor.38 39 In the present study, no statistically significant associations between CVD and cerebral infarction prevalence and diabetes mellitus were observed.
The atherogenic effects of arsenic have been well documented. Occupational exposure to inorganic arsenic through inhalation of polluted air from copper smelting and pesticide manufacturing was found to be associated with a moderate but not statistically significant excess mortality from ischemic heart disease and CVD.13 14 15 Inorganic arsenic ingested through drinking water has been related to the development of peripheral vascular disease and ischemic heart disease among arsenic-exposed residents in Taiwan,4 5 12 40 41 42 Chile,8 and Mexico7 and among Moselle (Germany) vintners exposed to inorganic arsenic through contaminated wine.11 However, the association between CVD and environmental exposure to arsenic has never been elucidated in previous studies. A statistically significant dose-response relationship between the prevalence of CVD and cerebral infarction and inorganic arsenic exposure through drinking well water was observed in the present study. Moreover, the association remained statistically significant after adjustment for other risk factors including age, sex, hypertension, diabetes mellitus, cigarette smoking, and alcohol consumption. On the basis of the striking dose-response relationship, it may be implied that CVD and cerebral infarction may be induced by long-term exposure to inorganic arsenic ingested through drinking well water.
Physical and chemical characteristics of well water, such as pH value
and levels of arsenic, sodium, calcium, magnesium, manganese, iron,
mercury, chromium, lead, nitrite and nitrate nitrogen,
fluoride, and bicarbonate, have been studied intensively in the
Lanyang Basin.43 Arsenic level was found to be the only
item that was significantly higher than the maximum allowable limit in
30% of well water in the study area. Arsenic is thus the main
chemical in the water responsible for the increased prevalence of CVD.
The mechanism of arsenic-induced CVD is yet to be elucidated. Inorganic
arsenic may increase CVD risk through its effects on
atherosclerosis directly or on CVD risk factors,
including hypertension and diabetes mellitus. The dose-response
relationship between long-term exposure to ingested inorganic arsenic
and risk of hypertension and diabetes mellitus has been reported in
recent studies.44 45 Additional studies are required to
examine whether there are direct effects of inorganic arsenic on the
atherogenic process through interference with lipid
metabolism, creation of endothelial
injuries, or induction of monoclonal expansion of smooth muscle cells.
Epidemiological studies have shown that arsenic and vinyl chloride
monomer seem to have a specific capability to cause various vascular
lesions, including angiosarcomas and atherosclerotic plaques. These
observations suggest that somatic mutation and cell proliferation may
play a role in the pathogenesis of atherosclerotic
plaque.46 The hypothesis that monoclonal expansion of
smooth muscle cells is a key process for
atherosclerosis induced by inorganic arsenic is
suggested by evidence of the dual effect of arsenic on carcinogenicity
and atherogenicity observed in our previous
studies.5 47
The chemical properties of arsenic are similar to those of nitrogen and phosphorus, which are important elements of DNA, RNA, and protein. Arsenate may hinder the normal functions of some enzymes that are regulated by the process of phosphorylation and dephosphorylation through disruption of the formation of ATP from ADP and orthophosphate. Arsenide is known to react strongly with sulfhydryl groups of proteins; it may interfere with the normal biochemical functions of proteins that are regulated by the formation of -S-S- bonds involving the cysteine side chains in the proteins.1 2 Whether arsenic may induce CVD through its interference with the structural or functional proteins involved in atherosclerosis requires further investigation.
| Acknowledgments |
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Received May 27, 1997; revision received June 24, 1997; accepted June 24, 1997.
| References |
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