Cardiology 64: 24-34 (1979)
Drinking Water Quality and Sudden Death: Observations from
West and East Finland
S. Punsar and M. J. Karvonen
Finnish Heart Association, Research Department, Helsinki
Supported by grants to M.J, Karvonen from the Finnish
Academy; from the Operation Red Heart Foundation of the Finnish
Lions' Organization; and from Oy Hartwall Ab, Manufacturers; and
to S. Punsar from Syddänsäätiö,
Helsinki, Finland.
Key Words. Water hardness - Coronary heart
disease Magnesium - Copper - Chromium
Abstract. Relationships of drinking water
quality to CHD and sudden death were studied in two rural areas
in western and eastern Finland. In the eastern area, drinking
water is particularly soft and contains less magnesium and
chromium but more copper than in the western area. A 15-year
follow-up of resident males showed a higher death rate from CHD
in the eastern area but no difference in the proportion of sudden
deaths. The data suggest that CHD may be associated with low
concentrations of magnesium and chromium in the drinking water,
but no definite relationship was found between water quality and
sudden death.
The mortality from coronary heart disease (CHD) varies widely
between populations. According to one hypothesis, these
differences are, in part, related to the degree of hardness of
drinking water (9, 11, 21). Such a causal relationship, however,
is unproven, and no agreement exists on the nature of the water
factor and the biological mechanism through which water quality
could operate (12, 15). It has also been suggested from mortality
statistics that the higher death rates in soft water areas might
be due to an excess of sudden deaths (1, 2, 4, 14).
Within Finland, there is a marked difference in the mortality
from CHD between the eastern and the southwestern parts of the
country (6, 13, 18). In a cohort study of two rural male
populations, one from east Finland, the other from southwestern
Finland carried over a 15-year period from 1959, the eastern
cohort experienced a death rate from CHD about twice as high as
the western cohort (7, 8). In 1970, we collected and analyzed
samples of drinking water in the two regions. In both areas,
drinking water is soft but much more so in the eastern area (16).
The levels of the water constituents were also studied with
reference to disease experience of the individuals in the cohorts
over the 10-year period from 1959 to 1969 (16). The concentration
of copper tended to be high and that of chromium tended to be low
in the drinking water of men who had developed CHD or died from
the disease. The findings on magnesium were equivocal.
For the present study, we used our 1970 data on the drinking
water quality of the two regions but extended the observations on
CHD to include 5 more years, 1969-1974. This gave us almost
double the number of CHD deaths as compared with the previous
study. An attempt was also made to examine the relationship of
water quality to sudden death. Particular attention was paid to
three elements: magnesium, copper and chromium.
Subjects and Methods
In two rural regions all resident men born between 1900 and
1919 were recruited in 1959 for a prospective investigation of
CHD. The two cohorts were followed up yearly for mortality data
and examined at 5-year intervals in 1964, 1969, and 1974 (7,
8).
In both areas, households draw drinking water from their own
wells. In 1970, drinking water samples were collected from 93
wells in the western area and from 234 wells in the eastern area.
The samples were analyzed for 22 water factors (16). The study
areas were divided into sub-areas, 10 in the west and 33 in the
east. Medians, representing the values for the drinking water in
the sub-areas, were calculated for each of the water
characteristics. All the subjects in a sub-area, including those
who had died earlier, were assigned the values of the sub-area
water (16). For this study on drinking water, however, only
subjects whose residence had not changed since 1959 were
included. The number of subjects who moved from their sub-area
after 1970 was small and they were not excluded from the
statistics. In the present study, data on magnesium, copper and
chromium were analyzed for possible associations with the
development of CHD and with the occurrence of sudden deaths in
the two cohorts, during the period 1959-1974.
Deaths between 1959 and 1974 were classified by cause, using
standard criteria (8). Copies of all death certificates were
obtained. When death had occurred in a hospital. the hospital
records were examined for the cause of death and for terminal
events. For deaths occurring outside hospital, the certifying
doctor, relatives of the deceased, or witnesses of death were
interviewed or contacted somehow. Thus, in the majority of deaths
ascribed to CHD, information additional to that on the death
certificate was obtained. A standardized classification was used
for the length of the terminal episode prior to death caused by
CHD. For the present purpose, sudden death was defined as
unexpected on the day of death and occurring within an hour of
the onset of acute symptoms.
The survivors were grouped according to their health status at
the time of the 15-year re-examination in 1974. CHD was diagnosed
when, in the absence of other heart disease, there was a history
of angina on effort, typical attack of chest pain (20), heart
failure, a resting ECG showing gross changes of QRS, ST or T
waves, or atrial fibrillation (16). A small number of subjects
were placed in the 'sick' categories although they had no
definite symptoms or signs of heart disease in 1974. These were
the men who upon the 10-year reexamination had fulfilled the
above disease criteria, or showed an abnormal ECG response to an
exercise test.
Results
Differences between the Two Areas
Table I shows the number of deaths grouped into three broad
categories for the two cohorts, for the entire period 1959-1974.
Total mortality was higher in the eastern population, and the
number of deaths caused by CHD was nearly twice as high in the
eastern cohort (14.79%) as in the western one (8.7%, p <
0.001).
Table 1. Deaths between 1959 and 1974. Men aged 40-59 in 1959
----------------------------------------------------------------
West Finland East Finland
----------------------------------------------------------------
Number of men identified in 1959 888 823
Total number of deaths
between 1959 and 1974 235 (26.5%) 251 (30.5%)
Coronary deaths 77 (8.7%) 121 (14.7%)
Other cardiac causes 12 (1.4%) 18 (2.2%)
Other causes 146 (16.4%) 112 (13.6%)
Table II describes the length of the terminal episode in
deaths caused by CHD. There was no significant difference between
the two cohorts in the proportion of men who died within an hour
of the onset of terminal symptoms, but the percentage of deaths
classified as caused by chronic heart failure was higher in the
east than in the west. The proportion of deaths with insufficient
information on the terminal episode was almost twice as high in
the west as in the east.
Table II. Length of terminal episode in CHD deaths
----------------------------------------------------------------
Length of terminal episode Number of men
-------------
West Finland East Finland
----------------------------------------------------------------
1 h or less 30 (52%) 45 (43%)
< 1 h 27 (47%) 50 (48%)
Chronic heart failure (CHD) 1 (2%) 10 (10%)
Total classified 58 (100%) 105 (100%)
----------------------------------------------------------------
Insufficient data 19 16
Total 77 121
Table III presents the data for the concentrations of
magnesium, copper and chromium in the drinking water in the two
areas. In the east, where the mortality from CHD is high, the
average concentrations of magnesium and chromium are lower, but
the concentration of copper is higher than in the west. Note that
the concentrations shown in table III are sub-area medians and as
such are lower than the average concentrations because the
original levels were positively skewed (16). The concentrations
in individual wells also had greater ranges than those presented
here. For example, the maximum concentrations of magnesium were:
west, 108 mg/l; east, 23 mg/l.
The observations presented in tables I-III show that the two
areas differ both in mortality caused by CHD and in the
concentrations of magnesium, copper and chromium in the drinking
water. On the other hand, the proportion of deaths which were
sudden was similar in the two populations. This would suggest
that if there is a relationship here between water quality and
CHD, it is not caused by an excess of sudden deaths in the
eastern area.
Differences within the Two Areas
The relationships between the concentrations of the three
elements in the drinking water and CHD or sudden deaths within
the two areas are presented in tables IV and V - the numbers are
smaller than those in the previous tables because water data were
not available for all subjects (I 6).
- = Lower than in the 'alive' group.
*p <0.05.
Men grouped according to the length of the terminal episode or
heart disease status in 1974.
Comparison with the 'no heart disease' group.
+ = Higher; - = lower than in the 'no HD' group.
*p < 0.05; **p < 0.01.
1 Includes 1 death from chronic heart failure.
2 Includes 8 deaths from chronic heart failure.
In the western area, the only statistically significant
finding was a low concentration of chromium in the drinking water
of the men who had died from CHD by 1974 (table IV). In the
eastern cohort, the concentration of magnesium was statistically
lower in the drinking water of the men who had died from CHD, as
compared with the 'alive' category. Within each region, the
pattern of concentration of magnesium, copper and chromium
confirmed the observations reached by comparing one region to the
other but most of the differences were not statistically
significant.
In table V the 'alive' group is broken down into three
categories on the basis of the cardiac status in 1974, whereas
the group of deaths caused by CHD is divided into clusters
according to the length of the terminal episode. For statistical
purposes, the 'no heart disease' category was used here as a
reference. The differences between the two CHD death categories
with known length of terminal episode ( < 1 or > 1 h) were
also tested for significance.
In the west, the water concentrations of chromium in all
subgroups of CHD death were low compared to the 'no HD' group but
the differences were not statistically significant (cf table IV).
The group of subjects alive with clinical signs of CHD had a high
water concentration of chromium. No significant associations were
found between any of the elements and the suddenness of death. In
the east, death from CHD, and survival with clinical signs of CHD
or other cardiac diseases were associated with low concentrations
of chromium in the drinking water. Again, none of the element
concentrations were associated with the suddenness of death.
Discussion
All three drinking water elements studied here have been
implicated as water factors (3, 5, 16). Along with calcium,
magnesium is the principal element affecting water hardness. In
the eastern area, where the mortality from CHD is high, the
drinking water is particularly soft and has low concentrations of
magnesium and chromium, elements which are considered to be
protective (3, 22, 23, 25). On the other hand, the concentration
of copper, which is thought to be harmful, is high (5). Other
drinking water constituents also occur in markedly different
concentrations in the two areas. In the east the levels of NO3,
K, Co, Ni and Ba are higher and those of Ca, Na, F (16) and of Si
(24) lower than in the west. Unpublished data show that the mean
concentration of Cd is higher in the west than in the east though
the difference is not statistically significant. Several of these
water constituents have also been suspected as water factors (15,
22, 24). In our previous study, magnesium, chromium and copper
had showed some associations with CHD within the two study areas
(16). With 5 more years of follow-up, the results were similar
except that the associations for copper were not statistically
significant.
Mortality statistics have suggested an increased proportion of
sudden deaths in soft water areas (1, 2, 4, 14). The results of
the present work on individual men do not indicate such an
association, nor was any of the three elements definitely related
to the suddenness of death. There are, however, several possible
sources of error in such data. Misclassification of causes of
death cannot entirely be avoided. The autopsy rate was less than
20% in the east, and about 25% in the west. However, evidence
from other sources indicates that the difference in the CHD death
rates between the two areas is real (6, 13, 18). The definition
of sudden death poses a more difficult problem. Witnesses are not
always available and their descriptions of the event are
notoriously inaccurate. In stressful characteristics, the two
populations are traditionally believed to react quite
differently, and this may cause a bias in the proportion of
sudden deaths in the two populations. However, it is unlikely
that such bias would affect the relationships within a
population.
A problem of prime importance in all water studies is the part
played by drinking water in the supply of the incriminated
elements (15). There are indications that under some
circumstances magnesium and chromium may occur in drinking water
in amounts that are large enough, compared to those present in
food, to be of nutritional importance (22, 25). Whether this is
the case in Finland remains an open question. Nonetheless, our
two populations seem to be ideally suitable for a water study
since the men lead a similar rural life, each probably getting
most of his drinking water from his own well. For the present
study, sub-area median concentrations, instead of concentrations
in the individual wells, were used as water data. Whether such
median values reflect the individual's exposure to the elements
studied more truly than the individual well concentration remains
a matter of conjecture (16). The use of medians decreases the
differences between the categories and between the two areas and
attenuates the relationships under study. In both areas, the
median concentrations of magnesium in the drinking water were on
the low side and the ranges were narrow, particularly in the
east. Yet there were indications that magnesium, along with
chromium and possibly copper, might be involved in the genesis of
CHD.
A further basic element for a study on drinking water is the
constancy of concentrations, which has received scant attention
(15). We had an opportunity to investigate this aspect of the
problem when, in 1974, 4 years after the collection of the
samples for the present study, the two cohorts were reexamined
and new drinking water samples were obtained. Unfortunately,
those 2 years represented two extremes as regards rainfall during
the periods immediately preceding water collection, particularly
in the eastern area. In 1974 the amount of rainfall in the three
preceding months was about 2 1/2 times that in 1970 in the east,
and in both areas large differences were present in water table
levels between the 2 years (10, 26). From the 1974 samples
several water constituents were analyzed and concentrations in
wells included on both occasions (west, n = 22; east, n = 46)
were compared to those of 1970. In spite of these complicating
factors the concentrations of bulk elements (Na, K, Ca, Mg) were
remarkably similar, and the correlations between the values of
the 2 study years were quite good. For magnesium, the correlation
coefficients (r) were 0.89 (p < 0.001) in the west and 0.58 (p
< 0.001) in the east. However, concentrations of chromium were
low in 1974 as compared to 1970, and the correlation coefficients
were not significant. Methodological difficulties involved in the
determination of chromium (19) may to some extent account for the
difference.
However, the concentrations of fluorine were also lower in
1974 than in 1970 with correlation coefficients being
non-significant, whereas excellent agreement was found with
previous values when samples stored from 1970 were re-analyzed.
No information is available on copper since copper was not
included in the later study. Obviously, the analytical
difficulties associated with chromium would obscure, rather than
clarify, any relationships with CHD. It may also be noted that
another study of the men of the two regions showed that they have
a particularly low excretion of cluomium in their urine, compared
with values found elsewhere (17).
In conclusion, our data support the hypothesis that the
quality of drinking water plays a part in the difference in
mortality from CHD between the two study areas. However, the
findings do not support the hypothesis that the alleged water
factors operate through an increase in the frequency of sudden
death.
References
1 Anderson, T.W. and Le Riche, W.H.: Sudden death from
ischemic heart disease in Ontario and its correlation with water
hardness and other factors. Can. med. Ass. J. 10-5: 155-160
(1971).
2 Anderson, T.W.; Le Riche, W.H., and MacKay, J.S.: Sudden
death and ischemic heart disease. Correlation with hardness of
local water supply. New Engl. J. Med. 280: 805 -807 (1969).
3 Chipperfield, B. and Chipperfield, J.R.: Heart-muscle
magnesium, potassium, and zinc concentrations after sudden death
from heart-disease. Lancet ii: 293-296(1973).
4 Crawford, M.D.; Clayton, D.G.; Stanley, F., and Shaper,
A.G.: An epidemiological study of sudden death in hard and soft
water areas. J. chron. Dis. 30.- 69 - 80 (1977).
5 Harman, D.: Hard and soft water and the incidence of sudden
death from ischemic heart disease: consideration of copper,
magnesium and calcium; in Seelig, Nutritional imbalances in
infant and adult disease. Mineral, vitamin D, and cholesterol.
Proc. 16th Annu. Meet. American College of Nutrition, New York
1975, pp. 1-7 (Spectrum Publications, New York 1977).
6 Kannisto, V.: Death causes as demographic factors in Finland
(in Finnish); thesis Helsinki (1974).
7 Karvonen, M.J.; Blomqvist, G.; Kallio, V.; Orma, E.; Punsar,
S.; Rautaharju, P.; Takkunen, J., and Keys, A.: Men in rural east
and west Finland; in Keys et al., Epidemiological studies related
to coronary heart disease: characteristics of men aged 40-59 in
seven countries. Acta med. scand., suppl. 460, pp. 169-190
(1967).
8 Karvonen, M.J.; Orma, E.; Punsar, S.; Kallio, V.; Arstila,
M.; Luomanmäki, K., and Takkunen, J.: Five-year experience
in Finland; in Keys, Coronary heart disease in seven countries.
Am. Heart. Ass. Monogr., vol. 29, pp. 52-62 (1970).
9 Kobayashi, J.: On geographical relationship between the
chemical nature of river water and death-rate from apoplexy. Ber.
Ohara Inst. landw. Biol. II: 12-21 (1957).
10 National Board of Waters, Finland: Personal commun.
11 Neri, L.C.; Hewitt, D., and Mandel, J.S.: Risk of sudden
death in soft water areas. Am. J. Epidem. 94: 101-104 (1971).
12 Neri, L.C.; Hewitt, D., and Schreiber, G.B.: Can
epidemiology elucidate the water story? Am. J. Epidem. 99: 75-88
(1974).
13 Partanen, T.: Statistics on cardiovascular diseases in
Finland (in Finnish). Finnish Heart Association, Helsinki
(1965).
14 Peterson, D.R.; Thompson, D.J., and Nam, J.M.: Water
hardness, arteriosclerotic heart disease and sudden death. Am. J.
Epidem. 92., 90-93 (1970).
15 Punsar, S.: Cardiovascular mortality and quality of
drinking water. An evaluation of the literature from an
epidemiological point of view. Work-environm.-hlth 10: 107125
(1973).
16 Punsar, S.; Erämetsä, O.; Karvonen, M.J.;
Ryhänen, A.; Hilska, P., and Vornamo, H.: Coronary heart
disease and drinking water. A search in two Finnish male cohorts
for epidemiologic evidence of a water factor. J. Cron. Dis. 28:
259-287 (1975).
17 Punsar, S.; Wolf, W.; Mertz, W., and Karvonen, M.J.:
Urinary chromium excretion and atherosclerotic manifestations in
two Finnish male populations. Ann.clin. Res. 9.79-83 (1977).
18 Puska, P.: Regional differences in cardiovascular death
rates (in Finnish). Suom. LääkLehti 27 3071-3075
(1972).
19 Report of a WHO Expert Committee: Trace elements in human
nutrition. WHO techn. Rep. Set. No. 532 (1973).
20 Rose, G.A. and Blackburn, H.: Cardiovascular survey methods
(WHO, Geneva 1968).
21 Schroeder, H.A.: Relation between mortality from
cardiovascular disease and treated water supplies. Variations in
states and 163 largest municipalities of the United States. J.
Am. Med. Ass. 172: 1902-1908 (1960).
22 Schroeder, H.A.: The role of trace elements in
cardiovascular diseases. Med. Clins N. Am. 58.- 381-390
(1974).
23 Schroeder, H.A.; Nason, A.P., and Tipton, I.H.: Chromium
deficiency as a factor in atherosclerosis. J. chron. Dis. 23:
123-142 (1970).
24 Schwarz, K.; Ricci, B.A.; Punsar, S., and Karvonen, M.J.:
Inverse relation of silicon in drinking water and atherosclerosis
in Finland. Lancet i., 538-539 (1977).
25 Seelig, M.S. and Heggtveit, H.A.: Magnesium
interrelationships in ischemic heart disease. WHO symposium on
the prevention of ischaemic heart disease: metabolic aspects
(1972).
26 The Finnish Meteorological Institute: Met. Yb., Finl. 1970:
Part la; 1974: Part la.
Dr. S. Punsar, MD, Finnish Heart Association, Research
Department, P.O. Box 196, SF-00121 Helsinki 12 (Finland)
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