Acta Med Scand 1984; 215: 477-9

Serum Magnesium in Greenland Eskimos BJARNE BO JEPPESEN, ANNIE BLACH and BENT HARVALD

From the Department of Clinical Chemistry, Slagelse County Hospital, Slagelse, and Department of Internal Medicine C , Odense Unviersity Hospital, Odense, Denmark

ABSTRACT. Jeppesen BB, Blach A, Harvald B. (Department of Clinical Chemistry, Slagelse County Hospital, Slagelse, and Department of Internal Medicine C, Odense University Hospital, Odense, Denmark.) Serum magnesium in Greenland Eskimos. Acta Med Scand 1984; 215: 477-9.

Serum magnesium in Greenland Eskimos living in Greenland is significantly higher (p<O.OOl) than in Greenlanders and Danes living in Denmark. Danes living in Greenland show intermediate values. The higher serum magnesium may be due to a high intake of nutrients from fish and sea mammals. A more complete intestinal absorption of magnesium caused by a low dietary calcium should also be considered. The high serum magnesium may contribute to the rare occurrence of urinary calculi in Grenlanders. Key words: Greenland Eskimos, serum magnesium, urinary calculi.

The average serum calcium level in Greenlanders living in Greenland is lower than in Danes and Greenlanders living in Denmark (1). It has been concluded that this low serum calcium level is probably due to a low calcium content in the Greenlandic diet. As the intestinal absorption of magnesium is facilitated by a low calcium diet because of competi- tion between the two divalent ions (2), it is of some interest to decide whether the low serum calcium in Greenlanders is reflected in the serum magnesium level. Serum magne- sium has therefore been determined in stored serum samples from the study populations examined in the calcium study.

STUDY POPULATION The following groups were examined. Greenland Eskimos: I. 46 healthy Greenlanders living in Godth%b/Nuuk, Greenland. 11. 25 healthy Greenlandic adolescents living in boarding schools in Denmark. 111. 23 Greenlandic inmates in psychiatric institutions in Denmark. Danes: IV. 16 healthy Danes living in Godth%b/Nuuk, Greenland. V . 32 outpatients from an otorhinolaryngology clinic in a Danish county hospital. VI. 39 inpatients in a Danish county hospital. VII. 10 inmates of a Danish asylum for mentally retarded.

Details of the groups have been given elsewhere (1). Ten persons in group I and 3 in group VI of the calcium study (1) have been left out because sufficient amounts of stored serum were not available for duplicate magnesium analyses.

METHODS Serum magnesium was determined by atom absorption photometry (Zeiss FL 6 Electrolyte Automat) with allowed deviation of 2.5 % in duplicate analysis. Serum magnesium values were corrected to a serum albumin concentration of 45 g/l by the equation:

S-Mg,,,,, (mmOlh) = S-Mg,,,. (mmoM)+0.007 (45-S-alb.,bs. (d1)).

Reference range for serum magnesium was 0.70-0.95 mmol/l. Serum albumin was determined photometrically with bromocresol green (L.K.B. filterphotometer

2074), allowed deviation 2 g/l in duplicate analysis. Reference range for serum albumin was 42-50 g/l. All analyses were performed in the same laboratory and by the same technician. Levels of

significance were determined by means of Student’s t-test.

478

RESULTS Table I summarizes the results of serum magnesium and serum albumin determinations in the seven groups. The highest serum magnesium level was found in Greenlanders living in Greenland, in whom it was significantly higher than in Greenlanders and Danes living in Denmark (I vs. 11, 111, V, VI, and VII p<O.OOl). Intermediate serum magnesium values were found in Danes living in Greenland, in whom serum magnesium was significantly lower than in Greenlanders living in Greenland (IV vs. I p<O.OS), and significantly higher than in Greenlanders and Danes living in Denmark (IV vs. I1 and V p<O.OOl, IV vs. I11 and VII p<O.Ol, IV vs. VI p<O.OS).

B . B. Jeppesen et al. Acta Med Scand 1984; 215

DISCUSSION

The finding of a high serum magnesium in Greenlanders fits well in with the low serum calcium demonstrated earlier. The fact that Greenlanders living in Denmark show values of serum magnesium not different from those of Danes living in Denmark strongly indicates that differences between groups must be due to environmental factors. This fits well in also with the approach to Greenlandic values by Danes living in Greenland.

The estimated daily nutritional requirement of magnesium is 15 mmol, about 30% of this amount is absorbed (3). In the Greenlandic diet, fish and meat of sea mammals are assumed to be the most important sources of magnesium. No studies exist, however, concerning the dietary magnesium intake in Greenland. Therefore it cannot be settled whether the high serum magnesium is due to a magnesium-rich diet or other factors. Thus a low dietary intake of calcium, which must be suspected in Greenlanders because of low content of dairy products in the diet, promotes the intestinal absorption of magnesium (2). In this context it should, however, be stressed that magnesium is primarily an intracellular ion and serum magnesium is not a good guide to body magnesium status. A high serum magnesium may just be a reflection of altered relations between extra- and intracellular magnesium. The fact that serum magnesium in Greenlanders living in Denmark is similar to that of Danes living in Denmark, whereas Danes living in Greenland have serum

Table I. Serum concentrations of magnesium and albumin (mean k S E M ) in Green- landers and Danes under different conditions of living

Mean age S-magnesium' S-albumin n (Y.) (mmolh) (EN

Greenlanders I. Living in Greenland 46 29.2 1.02f0.015 45.0f0.2

in Denmark 25 18.9 0.87f0.009 45.3k0.3

in Denmark 23 28.4 0.89k0.011 43.3f0.6

11. Adolescents in boarding schools

111. Inmates in psychiatric institutions

Danes IV. Living in Greenlnad 16 31.5 0.95+0.019 45.720.5 V. Outpatients from an otorhino-

laryngology clinic in a Danish county hospital 32 36.5 0.84+0.009 44.7f0.3

VI. Inpatients in a Danish county hospital 39 40.7 0.88f0.016 39.0f0.9

an asylum in Denmark 10 26.9 0.88f0.011 44.8k0.7 VII. Mentally retarded inmates of

Corrected to S-albumin concentration of 45 g/l.

Acta Med Scand 1984; 215 Serum magnesium in Greenland Eskimos 479

magnesium values approaching those of the Greenlandic population, strongly indicates that genetic factors are unimportant.

Magnesium is an essential activator of about 300 enzymes, among others enzymes using adenosine triphosphate for a substrate. Thus magnesium is a vital co-factor in the mainte- nance of several energy-demanding processes at the cellular level such as oxidative phosphorylation, neuromuscular excitability and muscle contraction. It could therefore be expected that the average serum magnesium level in a population might influence morbid- ity and mortality as a contributory epidemiologic factor.

There is ample opportunity for speculation connecting the high serum magnesium with a number of well described nosographic characteristics of the Greenlanders. Thus magne- sium delays platelet clumping and prolongs the clotting time of whole blood (4), which fits well in both with the bleeding tendency and the low incidence of ischaemic heart disease in Eskimos.

Already in 1929 Hammersten (5) demonstrated an increased in vitro solubility of calcium oxalate in the presence of magnesium. A preventive effect of magnesium administration to patients with recurrent renal stones has repeatedly been reported (6). The frequency of admission to hospital because of urinary calculi among Greenlanders is less than half that among Danes (7).

High serum magnesium levels have earlier been demonstrated in South African Bantus and Central Australian aborigines (8). Both of these populations are just as the Green- landers characterized by their low incidences of coronary heart disease. Caucasians living in the same geographic area as the Australian aborigines had even higher levels of serum magnesium, which underlines the environmental influence on serum magnesium.

The finding of a high serum magnesium in Greenlanders must for the time being be considered an isolated observation without any special importance in itself. The final interpretation, however, must await the patching together of a global geo-medical mosaic which will emerge with the ongoing accumulation of data.

ACKNOWLEDGEMENT The study has been supported by a grant from the Medical Research Foundation for West Zealand.

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2.

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Jeppesen BB, Harvald B. Serum calcium in Greenland Eskimos. Acta Med Scand 1983; 214:99-101. Alcock N, MacIntyre I. Interrelation of calcium and magnesium absorption. Clin Sci 1962;

Seelig MS. Magnesium requirements in human nutrition. Proceedings of 3rd International Sympo- sium on Magnesium. Baden-Baden 1981; 2647. Anstall HB. The effect of magnesium on blood coagulation in human subjects. Lancet 1959; 1: 814-5. Hammarsten G. On calcium oxalate and its solubility in the presence of inorganic salts with special reference to the occurrence of oxaluria. Copenhagen: Carlsberg Research Laboratory, 1929;

Johansson G. Magnesium and renal stone disease. Acta Med Scand 1982; 212 (Suppl661): 13-8. Jeppesen BB, Lynge P, Harvald B. Urinary calculi in Greenland Eskimos. Nordic Council for Arctic Medical Research Report. In press 1984. Chamock JS, Cassley-Smith J, Schwartz CJ. Serum magnesium-cholesterol relationships in the Central Australian aborigines and in Europeans with and without ischaemic heart disease. Aust J Exp Biol 1959; 37: 509-16.

22: 185-90.

17: 1-16.

Received Aug. 2, 1983.

Correspondence: B. B. Jeppesen, MD, Tjgimelundevej 17, Tjgimelunde, DK-4270 H@ng, Denmark.