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Magnesium 6:307-313;(1987)

Greenland, a Soft-Water Area with a Low Incidence of Ischemic Heart Death

Bjarne Bo Jeppesen

Sæby Hospital, Høng, Denmark

Key Words. Greenland · Soft-water area · Ischemic heart death · Calcium/magnesium ratio

Abstract. Present-time Greenlanders are living a stressful ‘westernized life’ complete with an elevated consumption of tobacco and alcohol. The drinking water in Greenland is extremely soft and the diet is very low in calcium (and probably magnesium) and rich in carbohydrate and fat. Despite these different predisposing factors, death from ischemic heart disease is 3-6 times less frequent than in Denmark. The serum calcium/magnesium ratio in Greenlanders is significantly lower than in Danes. Magnesium deficits in patients with acute myocardial infarction, as well as epidemiologically positive correlations between dietary calcium/magnesium ratios and ischemic heart death, are the basis for attributing the low incidence of ischemic heart death in Greenland to the low Greenlandic calcium/magnesium ratio in diet and blood serum. Other characteristics of the Greenlandic disease pattern include a low incidence of stones in kidney and urinary tract, few cases of diabetes mellitus, prolonged bleeding time, increased atrioventricular block and osteoporosis, all of which may also be related to a low calcium and high magnesium metabolic status.

2. Introduction

Factors predisposing to ischemic heart disease such as stress, smoking, alcohol, lack of physical activity, a high dietary carbohydrate and fat intake are to a high degree present in the Greenlandic daily life [3, 8, 10]. The Greenlandic drinking water is surface water and therefore soft, which further increases the risk for ischemic heart disease [23]. Nevertheless, ischemic heart disease appears to be less frequent in Greenland than in Denmark, although past studies have not taken age and sex factors into consideration [2, 3, 10, 17].

Deficiency in magnesium content in patients with acute myocardial infarction has been described [14], and a positive correlation has been shown epidemiologically between the dietary calcium/magnesium ratio and ischemic heart death [15]. The low serum calcium and high serum magnesium, shown earlier in Greenland residents [12, 12] might therefore be the cause of a lower incidence of ischemic heart disease [22].

The purpose of the present study is to determine the influence of age and sex factors on the incidence of ischemic heart death in Greenlanders as well as in Danes who live in Greenland, also to estimate the hardness of the Greenlandic drinking water, the calcium and magnesium content in the water and the diet, and to relate the serum calcium/magnesium ratio to the incidence of ischemic heart disease as well as other Greenlandic disease patterns [2, 3, 9, 11, 13, 17].

Materials and Methods

Materials

The incidences of ischemic heart disease in Greenland and in Bornholm were compared during the period 1976-1979 [25, 26]. Bornholm is the Danish county most resembling Greenland in terms of size of population and its relatively isolated position [7]. The populations of both islands are concentrated in small town communities along the coast, where fishing and related industries play an important role.

Climatically, Greenland belongs to the Arctic area, while Bornholm with its position in the Baltic has a temperate climate favoring agriculture. The Danish National Board of Health administers both islands and the criteria for death certificate diagnoses are identical. The Greenlandic Health Service is decentralized consisting of well-educated Danish doctors along the Greenlandic coast, each town having its own hospital. In Greenland there are 11 hospital beds, 11 nurses and 1 doctor per 1,000 inhabitants, while in Bornholm there are 4 hospital beds, 12 nurses and 2 doctors per 1,000 inhabitants. The public expenses for the health services are equal, i.e. 3,900 Danish crowns/inhabitant [5]. Due to lower requirements for hospitalization, most diagnoses appear with double incidence in Greenland compared to Denmark.

For Greenland, analyses of the drinking water are mean values obtained from the waterworks in Nuuk/Godthåb during the years 1978-1983 [16]. For Bornholm, the analyses of the water are mean values from several waterworks for the year l983 [6]. The intake of calcium and magnesium and the ratio of saturated and polyunsaturated fat in Greenlandic and Danish food were compared [ 10, 21]. The food intake in Greenland (Angmagssalik) from the year 1979, with a monopoly of European food import, made this statistic quite precise.

In Greenland, blood for serum analysis was taken from healthy males, 46 Greenlanders and 16 Danes living in NuuklGodthåb. In Denmark, the blood serum was obtained from 25 male Greenlandic boarding-school pupils, who had resided for at least 6 months in Denmark, and also from 32 Danish males at the ear-nose-throat outpatients’ clinic in Slagelse. Further detailed information about each group has been presented earlier [11, 12).

Methods

The criterion for heart disease as a cause of death was a death certificate, where the primary cause of death was one of the following WHO code numbers: 390-398, 400-404, 410-414, or 420-429. Autopsies are rarely performed in Greenland, whereas the causes of death in Bornholm are frequently autopsy-verified.

The hardness of the drinking water was determined by the content of calcium and magnesium and is defined by a Danish unit: 10 mg CaO in 1 liter of water or 7.19mg MgO in 1 liter of water. A Danish unit is equivalent to 17.85 USA hardness units. Very soft water has <29 US units, very hard water > 250 US units.

Serum calcium was determined by titration fluorometry (Corning Calcium Analyzer 940) with an allowed deviation of 0.04 mmol/l in double analyses. Serum calcium was corrected for serum albumin deviations from an albumin concentration of 45 g/l by the equation:

Serum calcium correlation (mmol/l)= [serum calcium observed, mmol/l] + 0.0163 (45-[albumin observed, g/l]).

Reference range equalled 2.20-2.50 mmol/l.

Serum magnesium was determined by nuclear absorption photometry (Zeiss FL Electrolyte Automate) with an allowed deviation of 2.5% in double analyses.

Jeppesen Table I

Serum magnesium was corrected for serum albumin deviations from an albumin concentration of 45 g/l by the equation:

Serum magnesium correlation (mmol/1) = [serum magnesium observed, mmol/l] + 0.007 (45-[serum albumin observed, g/l]).

Reference range equalled 0.70-0.95 mmol/l.

Serum albumin was determined photometrically by bromocresol green (L.K.B. filter photometer 2074) with an allowed deviation of 2 g/l in double analyses. Reference range equalled 42-50 g/l. Student’s t test was used for determination of statistical significance.

Results

The incidence of ischemic heart death (WHO 410, 412) in Greenland and in Bornholm is shown in table I. The death rate for males is 3-6 times higher in Bornholm. In Greenland the death rate for ischemic heart disease for males in the age group 45-64 years is 3 times as high for Greenlanders compared with Danes living in Greenland.

The incidences of acute myocardial infarction (WHO 410) and morbus cordis ischaemicus chronicus (WHO 412) are given in table II. Acute myocardial infarction for males is 4 times lower in Greenland for the age group of 30-44 years (table II); when subjects reach the age 45-64 years, the incidence has increased by a factor of 20 in both Greenland and Bornholm. Morbus cordis ischaemicus chronicus is 3 times lower for the age group of 30-44 years in Greenland, but its incidence increases with age by a factor 7 in both Greenland and Bornholm. The mortality rates for different heart diseases and for heart diseases as a whole are shown in table III. It can be seen that no significant male:female difference in the incidence of ischemic heart death (WHO 410) is evident in Greenland.

Jeppesen Table II

Jeppesen Table III

The hardness of the drinking-water, the daily intake of calcium and magnesium and the polyunsaturated/saturated fat ratio are shown in table IV. The water is extremely soft in Greenland and the calcium/magnesium ratio (weight basis) in food is half compared to the calcium/magnesium ratio in Denmark. The blood serum calcium/magnesium ratio (molar basis) within the individual population groups is shown in table V. The lowest serum calcium/magnesium ratio is seen in Greenlanders in Greenland, and the highest in Danes in Denmark. Greenlanders in Denmark presented the second highest serum calcium/magnesium ratio, which is not significantly different from that of Danes in Denmark. The Danes in Greenland take up a position in between.

Discussion

The population in Greenland is exposed to many of the stress factors that by tradition are regarded as predisposing to ischemic heart disease. The use of cigarettes in Greenland per inhibitant above 15 years of age is 10 cigarettes a day [8]. The intake of alcohol is 50% higher than in Denmark [8]. The blood pressure levels in Greenlanders do not, however, appear to be different from the levels in Danes [4], although the incidence of death from hypertension are lower in Greenland (table III).

Jeppesen Table IV

Jeppesen Table V

Heart disease is the third most frequent cause of death in Greenland following accidents and malignancies [3]. Back in 1933, attention was drawn to a beginning calcium deficit in Greenlanders [24]. Old Greenlandic provisions rich in calcium and vitamin D were increasingly replaced by ‘shop food’, lacking in calcium. Also, today dairy products, fresh fruit and vegetables are only a small part of the Greenlandic diet [10]. An increased incidence of osteoporosis and cataract could be explained by a low calcium intake.

It is a clinical experience that angina pectoris is rare in Greenland [3]. The remaining Greenlandic pattern of diseases is characterized by a low incidence of stones in kidney and urinary tracts, an extremely low incidence of diabetes mellitus and prolonged bleeding time [2, 3, 13].

Magnesium is thought to exert a therapeutic effect on angina pectoris [19]. Magnesium with its negative inotropic and calcium-antagonistic effects is regarded as a natural calcium antagonist [1a, 27]. The deficit of magnesium is suspected of playing a role in acute myocardial infarction [1b, 14, 22]. A low serum calcium and a high serum magnesium value are presumed to reduce the risk of stones in kidney and urinary tract [13]. A deficit of magnesium is prevalent in diabetes mellitus [18, 20]. In Greenland a calcium intake of 600 mg daily is equal to the recommended intake in Denmark, where the calicum intake is double this amount [21].

It is concluded that the prevalence of age-corrected ischemic heart death for males, including acute myocardial infarction, is 3-6 times lower in Greenland than in Denmark. This also applies to Danes settled in Greenland. The Greenlandic drinking water is extremely soft, the calcium/magnesium ratio in the diet is half compared to the ratio in Denmark and, in addition, the calcium/magnesium ratio in serum is significantly lower (p <0.001).

The special Greenlandic pattern of disease might, theroretically, be connected with a low serum calcium and a high serum magnesium level, which — in turn — might reflect the dietary intake of calcium and of magnesium. The low calcium/magnesium ratio in the water, food and serum in Greenland is, epidemiologically, in accordance with the low ischemic heart death rate [l5].

A screening of the Greenlandic serum for other minerals, trace elements, cholesterol and fatty acids might further contribute to the elucidation of the special Greenlandic disease pattern.

Acknowledgements

The skilful technical assistance of Jørn Otzen, The Danish National Board of Health, and Mette Madsen, The Danish Institute for Clinical Epidemiology, is gratefully acknowledged.

I thank Børge B. Jørgensen, Statens Seruminstitut, Den Grønlandske Kostskole I Tåstrup, Anderswænge, Amtshospitalet Vordingborg, and øre-næse-hals-afdelingen i Slagelse for their helpful cooperation.

Per Winther Petersen, Jonna Bredholt and Bent Harvald have given valuable support.

References

1a Altura, B.M.; Altura, B.T.: General anesthetics and magnesium ions as calcium antagonists on vascular smooth muscle; in Weiss, New perspectives on calcium antagonists, pp. 131-145 (American Physiological Society, Washington 1981).

lb Altura, B.M.; Altura, B.T.: Magnesium, electrolyte transport and coronary vascular tone. Drugs 4: suppl. 1, pp. 120-142 (1984).

2 Bang, H.O.; Dyerberg, J.: The lipid metabolism in Greenlanders. Meddr. Grønland Man. R. Soc. 2: 3-18 (1981).

3 Bennike, T.: Disease and health aspects under Equator and the Polar circle; in Circumpolar Health 81, pp. 229-240 (NOSAMF, Oulu 1982).

4 Bjergager, P.; Kroman, N.; Thygesen, K.; Harvald, B.: Blood pressure in Greenland eskimos. Ugeskr. Læg. 142: 2278-2280 (1980).

5 Bjerregaard, P.; Bille, H.: Sundhed for alle år 2000, Danmark, Færøerne og Grønland. Ugeskr. Leg. 146: 1887-1889 (1984).

6 Dansk Vandteknisk Forenings Sekretariat: Vandforsyningsstatestik 1983, 60 Vilh. Becks Vej, DK- 8260 Viby J. (Denmark).

7 Grønlands befolkning, 1. april 1976, 1. januar 1977-1979 og statistisk tabe1værk 1978: II, København 1978, 11 Sejerøgade, Postbox 2550, DK-2100 København Ø (Denmark).

8 Grønland, Kalaallit Nunaat, 1980, Årsberetning udarbejdet af ministeriet for Grønland, tabel 87, 116 (11. årgang 1981).

9 Harvald, B.; Hels, J.: Congenital malformations in Greenlandic Eskimos. Ugeskr. Læg. 132: 919-924 (1970).

10 Helms, P.: Changes in disease and food patterns in Angmagcsalik, 1949-1979; in Circumpolar Health 81, pp. 243-251 (NOSAMF, Oulu 1982).

11. Jeppesen, B.B.; Harvald, B.: Serum calcium in Greenland Eskimos. Acta med. scand. 214: 99-101 (1983).

12 .Jeppesen, B.B.; Blach, A.; Harvald, B.: Serum magnesium in Greenland Eskimos. Acta med. scand. 215: 477-479 (1984).

13 Jeppesen, B.B.; Lynge, P.; Harvald, B.: Urinary calculi in Greenland Eskimos. Arctic med. Res. 37: 30-33 (1984).

14 Jeppesen, B.B.: Magnesium status in patients with acute myocardial infarction: a pilot study. Magnesium 5: 95-100 (1986).

15 Karppanen, H.: Epidemiological studies on the relationship between magnesium intake and cardiovascular disease. Artery 9: 190-199 (1981).

16 Klinisk Vandanalyse. Dons R. Vanthnalytisk laboratorium, Grønlands tekniske organisation, 20 Hauser Plads. DK-l 127, København K (Denmark).

17 Kromann, N.; Green, A.: Epidemiological studies in the Upernavik district, Greenland. Acta med. scand. 208: 40 1-406 (1980).

18 Levin, G.E.: Mather, H.M.; Pilkington, T.R.E.: Tissue magnesium status in diabetes mellitus. Diabetologia 21: 131-134 (1981).

19 Makiel-Shapiro, B.; Bersohn, I.; Terner, P.E.: Parenteral magnesium phosphate therapy. Med. Proc. 2: 455-46 1 (1956).

20 Mellerup, E.T.: Insulin effects on calcium, magnesium and phosphate metabolism in rats. Acta endocr. 75: 748-755 (1974).

21 Levnedsmiddeltabeller og danskeres kostvaner 1985. I. Hovedresultater, No. 75 (Copenhagen 1985).

22 Seelig, M.; Heggtveit, A.: Magnesium interrelationships in ischaemic heart disease. A review. Am, J, clin. Nutr. 27: 59-79 (1974).

23 Stitt, F.W.; Clayton, D.G.; Crawford, M.D.; Morris J.N.: Clinical and biochemical indicators of cardiovascular disease among men living in hard and soft water areas. Lancet i: 122-126 (1973).

24 Sundhedsstyrelsens Aarsberetning for 1933 XX: 106-107 (København 1934). The Danish National Board of Health, 1. St. Kongensgade, DK-1264 København. K. (Denmark).

25 The Danish Institute for Clinical Epidemiology, 25 Svanemøllevej, DK-2 100 København Ø Denmark).

26 The Danish National Board of Health, 1. St. Kongensgade, DK-1264 København K. (Denmark),

27 Turlapaty, P.D.M.V.; Altura, B.M.: Magnesium deficiency produces spasms of coronary arteries: relationship to etiology of sudden death ischemic heart disease. Science 208: 198-200 (1980).


Received: September 2, 1986
Accepted: September 8, 1987

Bo Jeppesen
Tjørnelundevej 17
Tjørnelunde
DK-4270 Høng (Denmark)


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