International Journal of Epidemiology
©International Epidemlological Association 1988
Vol. 17, No. 3
Printed in Great Britain
Mortality from Ischaemic Heart
Disease and Cerebrovascular Disease
in Greenland
PETER BJERREGAARD* AND J0RN DYERBERGt
A line of scientific investigations on thromboembolic
and atherosclerotic disease has been based on the
observation that Greenlanders have a low incidence of
Ischaemic Heart Disease (IHD), and an increased
bleeding tendency, both phenomena attributed to the
intake of n-3 polyunsaturated fatty acids, abundant in
the Greenlandic diet.1-2 The evidence for a low incidence of IHD in Greenlanders has so far been based on
a few scientific reports3'4 and on official mortality statistics.5 The latter are not very detailed and do not allow a
distinction between mortality in native Greenlanders,
who make up approximately 80% of the population,
and Danes. Also, the validity of the Greenlandic mortality statistics has been questioned.'The recent establishment of a computerized death register for
Greenland allows a much more detailed analysis of
mortality data than hitherto available, at present for
the period 1968-83.7
for 1975-83 was the official register of the National
Board of Health of Denmark.
For the period 1968-83, 92% of the deaths were
registered by a death certificate and accordingly had a
diagnosis of cause of death. The causes of death were
coded in the National Board of Health by the same
officials who code the Danish death certificates, thus
ensuring a comparable coding practice. Causes of
death were coded according to the ICD (8th revision).
For 1968 all death certificates were recoded manually
as they were originally coded according to the ICD (7th
revision). Only the underlying cause of death was
considered.
Population data stem from the census of 1970 and
1976 and from the civil registration records of Greenland. They are believed to be fairly accurate. The
distinction between native Greenlanders and Danes is
customarily based on the place of birth. This is not a
perfect social or ethnic classification, but the vast
majority of native Greenlanders thus defined are
socially and racially Greenlanders of predominantly
Inuit origin. Rates are presented as age-specific mortality rates per 10 000. Direct age-standardization to
the average native population of Greenland 1968-83
was applied in Table 7. Confidence limits of rates were
calculated from tabulated values of the Poisson distribution, while those of ratios were calculated as
MATERIAL AND METHODS
The Greenlandic Death Register has information on
all deaths of people resident in Greenland at the time
of death. For the period 1968-74, the register was
established by one of the authors from information
from death certificates, parish registers and the civil
registration records of Greenland, while the register
RR(1±Z/X)- 8
* Dinish Institute for Clinical Epidemiology, Copenhagen, Denmark.
Reprint requests to Dr P. Bjerregaard, Kenya Expanded Programme
on Immunization, PO Box 20781, Nairobi, Kenya,
t Department of Clinical Chemistry, Aalborg Hospital, Section
North, 9000 Aalborg, Denmark.
RESULTS
Total mortality (1968-83) in native Greenlandic males
514
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Bjerregaard P (Danish Institute for Clinical Epidemiology, Copenhagen, Denmark) and Dyerberg J. Mortality from
ischaemic heart disease and cerebrovascular disease in Greenland. International Journal of Epidemiology 1988; 17:
514-519.
Mortality 1968-83 from Ischaemic Heart Disease (IHD) and Cerebrovascular Disease (CD) was studied in .native
Greenlanders. Mortality from IHD was lower in Greenland than in Denmark for both rrtales and females and especially
low in Greenlandic settlements. IHD mortality decreased during the period. Mortality from CD was higher in Greenland
than in Denmark with no certain time trend.
Living conditions, of which a high intake of seafood may be a key factor, and/or a genetic predisposition seem to
protect Greenlanders from IHD and to predispose them to CD.
515
MORTALITY FROM IHD AND CD IN GREENLAND
TABLE 1 Age-ttandardized mortality ratioi between Greenland (native Greenlanden, 1968-83) and Denmark (1980). Cardiovascular diseases and
all causes. Point estimates with 95% confidence intervals in brackets
Males
Females
Standardized
mortality ratio
7.4
36
23
4.5
(3.3-16.6)
(1.9-10.8)
1.2
1.2
8
(0.4-3.2)
8
(0.4-3.5)
0.6
194
0.9
(0.5-0.7)
169
(0.7-1.1)
4.4
116
4.8
(3.0-6.5)
93
(3.1-7.4)
1.6
2.4
30
42
(1.4-4.1)
(0.9-2.9)
1.1
0.8
10
(0.5-2.8)
8
(0.3-2.0)
1.0
394
1.4
(0.9-1.1)
343
(1.2-1.6)
3084
2.4
2.3
2201
(2.2-2.5)
(2.3-2.6)
living in Greenland was 2.4 times higher than that of
Danish males living in Denmark (1980); for females
the ratio was 2.3 (Table 1). These ratios cover pronounced differences between causes of death. In particular, infectious diseases and accidents were
registered frequently as causes of death in Greenland
compared with Denmark. The Greenland/Danish
ratio for total cardiovascular mortality was 1.0 and 1.4
for males and females, respectively, but this covered
ratios of 4.4 to 7.4 for rheumatic fever and 'other heart
diseases' and 0.6 to 0.9 for IHD.
Mortality rates from IHD was lower in native
Greenlanders living in Greenland than in Danes living
No.
in Denmark in all age groups and both sexes (Table 2).
The Greenland/Denmark ratio was below 0.5 except in
15-44 year old females, where rates were very low in
both ethnic groups. When the percentage of deaths
from IHD are compared even lower ratios are noted.
The pattern of mortality from IHD was similar in
Greenlanders and Danes: the mortality rate increased
rapidly with age in both sexes and was higher in males
than in females. Also, in both populations the difference between males and females diminished with age.
The time trend of mortality from LHD in native
Greenlanders is shown in Table 3. For both males and
females in all three age groups there was a substantial
TABLE 2 Mortality rates per 10 000 person-years and percentage of deaths from IHD (ICD 410-414) in native Greenlanden Uving in Greenland
(1979-83) and population of Denmark (1980). Point estimates with 95% confidence intervals in brackets
Age group
15-44
Rate
Males
Greenland
Denmark
Greenland/
Denmark ratio
Females
Greenland
Denmark
Greenland/
Denmark ratio
% of deaths
0.5
0.7
(0.1-1.5)
(0.1-2.1)
1.0
0.5
6.5
0.1
(0.2-1.6)
(0.04-0.3)
0.2
0.7
(0-0.7)
(0-2.6)
0.2
0.9
2.3
0.3
(0.1-6.5)
(0.1-2.0)
65+
45-64
No.
3
114
1
23
Rate
% of deaths
12.0
(7.0-19.3)
38.7
(3.9-10.7)
32.8
0.3
0.2
(0.2-0 S)
(0.1-0.3)
6.7
4.8
3.9
(1.9-9.8)
(1.6-8.0)
14.1
9.8
0.5
(0.2-1.0)
0.3
(0.1-0.5)
No.
17
2063
Rate
% of deaths
115.7
(83.8-155.9)
247.3
13.5
(9.8-18.2)
35.8
0.5
7
549
(0.3-0.5)
63.9
(44J-89.3)
158.9
10.3
(7.1-14.4)
33.1
(0.3-0.6)
43
7710
0.4
(0.3-0.6)
0.4
No.
0.3
(0.2-0.4)
34
6775
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Rheumatic fever and chronic rheumatic heart disease
(ICD 390-398)
Hypertensive disease
(ICD 40O-4O4)
Iichaemic heart disease
(ICD 410-414)
Other heart A™*****
(ICD 420-429)
Diseases of arteries, arteriola and capillaries
(ICD 440-448)
Other ditrasci of circulatory system
(ICD 450-458)
Total cardiovascular diseases
(ICD 390-429. 440-458)
All causes
Standardized
mortality ratio
No.
516
INTERNATIONAL JOURNAL OF EPIDEMIOLOGY
TAILE 3 Mortality rates per 10 000 person-years from 1HD (1CD 410-414) in native Gnenlanden
with 95% confidence intervals in bracket!
1968-72
Age group
15-44
No.
1.1
4
Rate
45-64
Males
Females
65+
Males
Female*
No.
2
0.4
(0.3-2.7)
(0-13)
0.3
Females
1979-83
1973-78
Rate
Miles
living in Greenland (1968-83). Point estimates
1
0.6
11
37
54
reduction in mortality rates over the years 1968/72 to
1979/83. The decrease was on average 40%, but only
statistically significant for females in the 65+ age
group.
Danes make up 20% of the population of Greenland, but account for only 5% of deaths because many
Danes in Greenland only stay for a few years while
employed in government services or private companies
and return to Denmark if they become seriously ill. In
spite of this the mortality rate for IHD in Danish males
living in Greenland was as high or even higher than
that of Greenlandic males. The proportion of deaths
from IHD in the Danish males living in Greenland was
similar to that of Danes living in Denmark and much
higher than that of the native Greenlanders (Table 4).
Cerebrovascular disease (CD) can be haemorrhagic
or ischaemic and it is difficult to distinguish the two
types from purely clinical criteria. As autopsy is very
infrequently performed in Greenland the differentiation between the two types in Greenland is highly
uncertain. In Greenland around 40% of CD deaths
were diagnosed as cerebral haemorrhage and 10% as
thrombotic cerebrovascular disease as opposed to 30%
0.5
3
(0.1-1.5)
(0.1-1.7)
16.2
(10.3-24.4)
92
(5.0-15.4)
125.3
(91.7-167.1)
82.1
(59.7-110.2)
19
No.
3
0.2
1
23
(0-0.7)
12.0
(7.0-19.3)
17
4.8
7
14
(1.9-9.8)
115.7
(83.8-155.9)
63.9
(44.3-89.3)
46
44
43
34
and 15%, respectively, in Denmark. The percentages
were similar for males and females.
Mortality rates from CD, including cerebral haemorrhage, thrombotic cerebrovascular disease and
unspecified cerebrovascular disease, was consistently
higher in native Greenlanders living in Greenland than
in Danes living in Denmark, on average twice as high
(Table 5). Also for this disease the mortality rate in
males was higher than in females, the difference
decreasing with age. No statistically significant alteration in the mortality rate from CD was noted from
1968/72 to 1979/83 (Table 6).
Age-standardized mortality rates from IHD and CD
were compared between Denmark and Greenlandic
towns and settlements (Table 7). IHD was less frequent in settlements than in towns for both males and
females, but this was statistically significant only in
females. IHD mortality rate in males of Denmark was
higher than in both towns and settlements in Greenland, but for females there was no difference between
Denmark and Greenlandic towns. CD was less frequent in settlements than in towns for males, but no
difference was observed for females. For both sexes,
TABLE 4 Mortality from IHD (1CD 410-414) in native Greenlanders living in Greenland (1968-83), Dana living in Greenland (1968-83) and
population of Denmark (1980). Rates per 10000 penon-yean and percentage of deaths. Males only. Point estimates with 95% confidence intervals in
brackets
Age group
15-44
Rate
Grecnlandcn
Danes in Greenland
Danes
% of deaths
0.6
0.9
(0.3-1.1)
(0.4-1.7)
1.3
6.7
(0.6-2.5)
(3.1-12.7)
1.0
6.5
45-64
No.
9
9
114
Rate
% of deaths
15.6
9.0
(11.9-20.1)
12.9
(7.2-21.3)
38.7
(6.9-11.6)
19.7
(11.1-32.6)
32.8
65+
No.
59
15
2063
Rate
% of deaths
126.2
16.4
(105.2-150.3) (13.7-19.6)
195.3
41.7
(93.8-359.2) (20.0-76.6)
35.8
247.3
No.
126
10
7710
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(0-1.0)
19.9
(12.0-31.0)
10.1
(5.0-18.0)
143.1
(100.8-197.3)
151.7
(114.0-197.9)
Rate
517
MOETALTTY FROM IHD AND CD IN GREENLAND
TABU 3 Mortality rates per 10000 penon-yean from CD (ICD 431-438) in native Greenlandtrs living in Greenland (1979-83) and population of
Denmark (1980). Point estimates with 95% confidence interval] in bracket!
Age group
15-44
65+
45-64
V
No.
Rate
Rate
No.
Males
Greenland
0.3
2
12.7
(7.6-20.1)
18
Denmark
(0-1.2)
0.2
22
4.3
3.0
230
1.8
(0.4-7.4)
(1.9-4.7)
Orttnland/Denmarfc ratio
Females
Greenland
2
0.4
7
0.1
5.8
(1.5-23 2)
9
161
DISCUSSION
The validity of Greenlandic mortality statistics is not
high, primarily because most deaths occur at home or
in small hospitals with limited diagnostic facilities, and
because autopsy is only occasionally performed. Mortality analyses should not be conducted at too detailed
a diagnostic level. The predictive value of the diagnose
'Heart Disease' on a death certificate has been estimated as only 0.55 while the sensitivity was 0.92; corresponding figures for CD were 0.87 and 0.93.' There is
considerable overdiagnosing of all heart disease and,
because it makes up 65% of the diagnoses within this
group, consequently of IHD. This further strengthens
the observation that mortality rates from IHD in native
95.9
(71.4-126.1)
58.1
51
2479
1.6
(1.3-2J)
(1.1-4.1)
Danish CD mortality rates were considerably lower
than rates from Greenlandic towns and settlements.
2023
(1.5-2.6)
6.1
2.9
2.1
47
Greenlanders are considerably lower than in Danes,
who have rates similar to those of other Western European and North American populations. As the absolute number of deaths is so small in Greenland it has
not been possible to analyse the validity of diagnoses in
different periods or regions; if such differences exist it
may introduce bias when mortality rates are compared
between periods or regions. The low mortality rate
from IHD is supported by clinical observations of a low
incidence of acute myocardial infarction and other
forms of M D . M * " To what extent the high mortality
rate from CD is caused by thrombotic or haemorrhagic
disease is uncertain. The higher proportion of presumed haemorrhage in Greenlanders may give an
indication,12 but the diagnostic distinction is not firmly
based.
An important point to note is that even though the
TABLB 6 Mortality rataper 10 000 penon-yean from CD (ICD 431-438) in native Greenlanders living in Greenland (1968-83). Point estimates with
95% confidence intervals in brackets
1973-78
1968-72
Age group
15-44
Mates
Female*
45-64
Mates
Females
65+
Mates
Females
Rate
1.3
(0.4-3.1)
0.8
(0.2-2.4)
12.5
(6.5-21.9)
9.1
(4.4-16.8)
119.9
(81.5-170.2)
106.7
(75.5-146.5)
No.
5
Rate
0.2
1979-83
No.
1.2
2
6
0.4
2
9
(0-1.3)
12.7
(7.6-20.1)
18
6.1
9
(0.4-2.5)
12
10
31
38
6.4
(2.9-12.1)
8.5
(4.5-14.6)
125.3
(91.7-167.1)
85.9
(62.9-114.5)
No.
03
(0-1.2)
1
(0-0.7)
3
Rate
13
46
46
(2.8-11.6)
126.5
(92.9-168.2)
95.9
(71.4-126.1)
47
51
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Dennurk
Greenland/Denmark ratio
126.5
(92.9-168.2)
64.9
No.
1.9
(2.8-11.6)
(0-1.3)
Rate
518
INTERNATIONAL JOURNAL OF EPIDEMIOLOGY
TABLE 7 Age-standardized mortality rates per 10 000 person-years. Direct standardization to average native population of Greenland 1968-83.
Native Greenlanders living in towns and settlements of Greenland (1968-83), Denmark (1980). Point estimates with 95% confidence intervals in
brackets
Cerebrovascular disease
iKhaemfc heart disease
Mala
Standardized
rate
Greenland
Settlement!
Towns
Denmark
Town/settlement ratio
No.
5.3
6.2
57
137
10.0
9887
1.2
(0.9-1.5)
Males
Females
Standardized
rate
No.
3.2
5.8
5.4
1.8
25
144
7347
(1.2-2.6)
3.1
6.4
1.8
2.1
(1.5-3.0)
No.
32
139
2275
Standardized
rate
5.8
5.3
1.9
0.9
No.
45
133
2647
(0.7-1.2)
overdiagnosing, in spite of its present high level, could
have declined due to a better understanding of the
different morbidity patterns in Greenland and Western Europe, and to the recent availability of more
sophisticated diagnostic equipment.
Living conditions in Greenland vary greatly between
towns, where life to some extent is much like that in
Western Europe, and settlements where life is more
traditionally Greenlandic. In particular, the diet in the
settlements mainly comprises fish and/or sea mammals. Compared with Danish habits and with what is
common in most European countries, the intake of
seafood in the Greenland towns is, however, substantially higher. Mortality differences between towns and
settlements were pronounced for IHD in females and
for CD in males.
Thesefindingscould be interpreted in the following
way. Living conditions in Greenland among which the
high intake of fish and sea mammals may be a key
factor, and/or genetic predisposition, protect Greenlanders from LHD and predispose them to CD. Protection from IHD has increased in recent decades. The
protective factor for IHD is operating for males in both
towns and settlements, but for females in settlements
only, while the predisposing factor for CD is operating
for all Greenlanders irrespective of their place of residence, but it is most pronounced for males living in
towns. A differentiation between the influence of
external factors and genetic disposition would be possible through an analysis of mortality rates of expatriate
Greenlanders, but the very small number of these and
difficulties in terms of identification of the subpopulations have so far frustrated any attempt to perform this
analysis.
1
REFERENCES
Bang H O, Dyerberg J. The lipid metabolism in Greenlanders.
Meddr Grtnland, Man A Soc 1981; 2; 1-18.
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mortality rate from IHD is much lower in native
Greenlanders living in Greenland than in Danes living
in Denmark, and that from CD higher, the age/sex
patterns still remain similar in the two populations, in
particular a male:female rate ratio above 1, declining
with age.
Some previous studies of mortality from IHD in
Greenland and Denmark compared percentages of
deaths from this cause and found even lower Greenland/Denmark ratios. This is the reason why percentages were included in Tables 2 and 4. A comparison of
percentages, however, does not give an epidemiologically correct picture; in the present case the
percentage of IHD deaths in Greenland is low not only
because of few deaths from IHD, but also because of a
large number of deaths from other causes: the numerator is small and the denominator is large.
Mortality rates from IHD have declined over the last
two decade«. This is surprising as the proportion of
people living in towns, where mortality rates are higher
than in settlements, has been steadily increasing. Also,
living conditions have become increasingly westernized in both towns and settlements. It is, in this
respect, interesting to compare with the computations
of Kromhout et a/,13 who found an inverse relationship
between fish intake and coronary deaths in Holland
over a 20-year period, even at a relatively low level of
fish intake. The 'dilution' of the native Greenlandic life
pattern by urbanization does not seem to adversely
influence mortality rates from IHD. It must, however,
be realized that the concentration of the population of
Greenland in towns with subsequent westernization of
lifestyle and eating habits did not start until 30 years
ago, so the majority of people who died from IHD
during the period of study had spent most of their lives
in a traditional Greenlandic community. Another
reason for the recorded decline in mortality rate from
IHD in recent decades in Greenland could be that
Standardized
rate
Females
MORTALITY FROM IHD AND CD IN GREENLAND
2
DyerbergJ. Linotenate-derived polyunsaturated fatty adds and prevention of atherosclerosis. Nutr Rev 1986; 44: 125-34.
'Kromann N, Green A. Epidemiokigical itudies in tbe Upernavik
District, Greenland. Aaa Med Scand 1980; 208: 401-6.
'Bjerregaard P, BJerregaard B. Disease pattern in Upenuvik in
relation to bousing cooditioni and social group. Meddr Grtnland, ManASoc 1985; 8:1-20.
3
The State of 'Health in Greenland. Annual Report from tbe Chief
Medical Officer in Greenland, 1950-85.
* Hetweg-Lanen K. Tbe validity of the mortality statistics in Greenland with special reference to Ischaemic Heart Disease. Ara
Med Res 1984; 38: 43-5.
7
Bjerregaard P. Grtnlandsk d«diaanagsregister. Ugeskr laeger 1985;
147: 3742.
•Rothman J K. Modem epidemiology. Boston, Toronto, Little,
Brown and Co., 1986.
519
' Bjerregaard P. Validity of Greenlandic mortality statistics. Ara Med
Res 1986; 42: 18-24.
Sagild U, Jespenen C S, Littauer J. Hjertesygdomme paa Grinland.
Nord Med 1966; 75: 7\6.
" Miktrrtrn F. Coronary heart disease in Greenland. Nord CouncArc
Med Res Rep 1974; 7: 36-9.
a
Dyerberg J, Bang H O. Haemostatic function and platelet potyunsaturated fatty acids in Eskimos. Lancet 1979; 2: 433-5.
u
Krombout D, Bosscnieter E B, Coulander C de L, The inrerse
relation betweenfishconsumption and 20-year mortality from
coronary heart daeve. N Engl J Med 1985; 3U: 1205-9.
a
(Revised version received June 1987)
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