Time-related changes in magnesium content and magnesium/calcium ratio of Finnish agricultural soil associated inversely with human CHD in 1961-1990 

Research Article


Time-related changes in magnesium content and magnesium/calcium ratio of Finnish agricultural soil associated inversely with human CHD in 1961-1990 

Corresponding author:     Dr. Toysa Timo, Pohjolank 15, 74100 Iisalmi, Finland,Tel: +358-440-676-426; Email: timo.toysa@fimnet.fi

Abstract

Because of reported associations of Mg with cardiovascular diseases (CVD), we assessed changes in soil Mg and Mg/Ca ratio
with human CHD in order to clarify, whether these soil parameters could be associated with the human CHD epidemic in Finland.

Human CHD and soil statistics are based on old data. Soil Mg and Mg/Ca ratio values are assessed by six successive 5 year periods from 1961 to 1990 (1961-1965, 1966-1970, etc). Mg has been included in basic samples (including Ca and K) since 1986, before it the number of Mg samples was lower and its distribution differed from basic samples. Soil-type-specific data are available from periods 1966-1970, 1976-1980 and 1986-1990. By benefiting the soil-type-distribution data from 1986-1990 and soiltype specific Mg and Ca values from these three periods we calculated adjusted Mg and Mg/Ca values for periods 1966-1970 and 1976-1980 (respective values for 1986-1990 were readily given).

Results

In original data soil Mg and Mg/Ca were decreasing in the 1960’s and increasing after that. Human CHD associated inversely with these soil values. In original data soil Mg explained 98 % (p < 0.001) of male CHD (M.CHD) and 80 % (p = 0.017) of female (F.CHD) during 1961-1990. Soil Mg/Ca explained 93 % (p = 0.002) variation in M.CHD and 70 % (p = 0.039) in F.CHD. By soil-type adjusted soil Mg and Mg/Ca confirm their increase in 1966-1990 during CHD reduction.

Conclusion

Magnesium status of Finnish agricultural soils associated inversely with human CHD in 1961-1990 and could be one causative factor of the Finnish CHD epidemic.

Keywords: CHD; Mg; Mg/Ca; Agriculture; Soil

Abbreviations

Adjusted Mg: ‘Mg.D.(86-90)’ (look down), respectively adjusted Ca and Mg/Ca;

AMI: Acute Myocardial Infarction;

ATP: Adenosine triphosphate;

Basic samples: Basic samples from agricultural soils (Included the same number of Ca, K all the time, since 1986 the same

number of Mg, too);

Ca: Calcium (mEq/L in agricultural soil);

CHD: two purposes: 1) Coronary Heart Disease or 2) CHD Mortality;

CVD: Cardio Vascular Disease;

exchangeable (soluble) (Ca, Mg,K) soil values: Determined by using acetic acid ammonium acetate buffer (0.5 M, pH 4.65);

E – expected value of regression (e.g. M.CHD.E[(Mg/Ca).soil]);

F as a prefix – female (e.g. F.CHD – female CHD);

HDL: High-Density Lipoprotein Cholesterol;

K: Potassium (mEq/L in agricultural soil);

LDL: Low-Density Lipoprotein Cholesterol;

M as a prefix: Male (e.g. M.CHD – male CHD);

Mg: Magnesium (mEq/L in agricultural soil), Mg samples – Mg

samples from agricultural soils (number of Mg samples was

lower than basic samples until 1985);

Mg.D.(86-90): By proportional soil-type distribution from

period 1986-1990 weighted soil-type specific Mg values (for

periods 1966-1970, 1976-1980 and 1986-1990); respectively

by Ca.D.(86-90);

R: Pearson Correlations [in associations (R)];

Soils: Agricultural soils

Introduction

Veterinary surgeon Nuoranne found trend-like associations between Mg deficiency in soil and fodder values with pig cardiac and other symptoms. Through his suggestions, Mg supplementation of fodder was increased since 1972. He wrote that “serious attention should be paid to the possibility of the respective existence of Mg-deficiency in humans” [1].

Annual Mg-supplementation of Finnish agricultural soils before 1972 has been estimated to be about 15 kg/ha, lower than the estimated losses via yields and leaching (25-30 kg/ha) [2]. 1972-1980 liming agents were mainly changed to dolomites, which increased annual Mg supplementation via liming agents  from 4 to 25 kg/ha and put the Mg-balance on the positive  side [2].

The fatal CVD risk of human populations has been generally predicted by parameters like gender, age, smoking, systolic BP, cholesterol and total cholesterol: HDL cholesterol ratio [3]. Several associations of Mg with CVD events have been reported: Decreased tissue magnesium in sublingual epithelial cells [4] and femoral muscles [5] have been reported in connection with vascular pathology. Mg has been directly or non-directly known to be associated with CVD risk factors [3]: Mg supplementation has been reported to decrease systolic and diastolic blood pressure in humans [6]. Proper tissue Mg can work as an “on-demand-antioxidant” against oxidative stress and a protector against lipid peroxidation and ATP deficiency [7]. Because oxidized LDL can increase tissue LDL/HDL ratio [8], total cholesterol/HDL-cholesterol could to some extend indicate tissue Mg level. Additionally, Mg can reduce mortality from acute myocardial infarction by reducing serious arrhythmias and left ventricular heart failure, as well as give some protection against platelet-dependent thrombosis [9]. In this study, we assessed changes of Mg and Mg/Ca ratio in agricultural soils, in order to clarify whether they could explain changes in the human CHD during 1961-1990.

Materials and Methods

Age-adjusted CHD of 35-64 years old females (F.CHD) and men (M.CHD) in 1960-1992 are from Valkonen and Martikainen (1990) [10] and Statistics Finland [11], (Table 1 and Figure 1).

Table 1. Age adjusted CHD mortality of 35-64 y old women (F) and men (M) in Finland during 1960-1992

Figure 1. represents changes in CHD of middle-aged females and males in Finland during 1960-1992. (Note the different scales!)

Female CHD was about 1/5 of male CHD. M.CHD and F.CHD were first increasing. Both begun to decline coincidentallysince 1967. The decline of F.CHD was faster until 1983. The decline of M.CHD seems to accelerate since 1985. After stagnationin 1983-1987 decline of F.CHD was faster than by M.CHD (Figure 1).

Ca, Mg and K of agricultural soil in 1961-1990

Agricultural soil exchangeable (soluble) Ca, Mg and K (meansof all Finnish samples) are from Eurofins Viljavuuspalvelu Oyby 5 years periods (1961-1965, 1966-1970, etc) [12] (Table 2, Figure 2). Figure 2 shows data from 1961-1995, but in statisticalassessment is excluded period (1991-1995), because of active medical treatments of CHD.

Mg samples were collected separately from basic samples including(e.g. Ca and K) before 1986. Detailed data including Ca,Mg and K values of different soil-types and soil-type distribution are from three periods: 1966-70, 1976-1980 and 1986-1990. Data from 1966-1970 shows that N of total samples was ca 380,000 and N of Mg samples ca 33,000 [13], in1976-1980 the respective numbers were 510,000 and 170,000 [14]. Anumber of basic (and Mg) samples from 1986-1990 amounted up to about 640,000 [15]. Detailed data from periods 1961-1965, 1971-1975 and 1981-1985 are not available.

Results

Agricultural soil parameters and human CHD

Table 3. Shows inverse and significant associations of soil Mg, Mg/Ca and Mg/(Ca+Mg+K) with F.CHD and M.CHD. These associations with M.CHD were stronger than with F.CHD. (Figure 1 and Figure 2). Soil Ca associated non-significantly with female and male CHD. K associated significantly (p = 0.045) with a female, but non-significantly with male CHD. Combined regressions by [Ca;Mg;K] explained 99.1 % (p = 0.039) variation in F.CHD and 99.5 % (p = 0.007) in M.CHD. In combined regressions coefficients of Ca were positive and by the others negative.

Discussion

Soil Mg, Mg/Ca ratio and human CHD

Soil Mg and Mg/Ca associated inversely and significantly with male and female CHD (Figure 1 and Figure 2) and explained significant variation in human CHD (Table 3, Figure 3). Associations by Ca and K were weaker (p > 0.045).

The decreasing trend of soil Mg and Mg/Ca was changed increasing in the 1970’s. The lower number of Mg to Ca and K samples caused bias, which obviously was underestimation: Mg samples were supposedly more often taken because of suspicion of Mg deficiency and less from clay soils, which were known to be rich in Mg [13]. The last suspicion was verified by the soil distribution data (Figure 4).

By increasing the number of samples between periods 1966-1970 and 1976-1980 [13,14] the proportion of clay soils in basic samples first decreased from 18 to 15 %. The respective decrease in Mg samples was from 13 to 11 %. It is supposed that in 1976-1980 clay soil proportion (15 %) is an underestimation and the distribution in 1986-1990 better reflects the real soil-type distribution in earlier periods, too. When soiltype specific Mg values from periods 1966-1970 and 1976- 1980 are weighted by soil-type proportions in 1986-1990, we get adjusted estimates, “Mg.D.(86-90)” values for periods 1966-1970 and 1976-1980, the same respectively with Ca (and Mg/Ca). We have no tools to evaluate more proper values for periods 1961-1965, 1971-1975 or 1981-1985. Mg.D.(86- 90) (Figure 5) and (Mg/Ca).D.(86-90) values (Figure 6) seem to confirm that Mg and Mg/Ca really increased between periods 1966-1970, 1976-1980 and 1986-1990.

Anyhow by the data of Jokinen [2], it was expected that the lowest Mg or Mg/Ca values should have been occurred during the first half of the 1970’s. Additionally, to biased sampling, this could be explained via a shift of agricultural activity away from the poorest soils, which was accelerated in 1969 by the law concerning limitations on the use of agricultural fields [16] and increased recycled Mg through increased Mg supplementation in fodder since 1972 [1]. (The law [16] was given because of overproduction caused mainly by a large-scale mechanization, e.g. reduction of 300,000 horses [17,18], which liberated agricultural fields for food supply approximately to 3 million people, who needed less energy in their work). Arable land – in spite of increased population – was reduced by ca 6 % between 1968-1973 [19], i.e. between periods 1966-1970 and 1971-1975 (Figure 7).

Changes in strong acid soluble mineral elements were not available and are out of the scope of this article.

These corrected estimates confirm the suggestion that during the declining CHD epidemics (1967-1990) soil Mg and Mg/Ca values were increasing. The suggestions on underestimation of Mg values in the 1960’s concerns the period 1961-1965, too: it is obvious that Mg and Mg/Ca were decreasing in the 1960’s. By the available data [12] (Figure 2) soil Mg balance was positive until the period 1991-1995 when Mg included in basic samples.

The faster decline of female CHD could possibly be explained by the lower per cent of female smokers (generally known), when smoking increased in Finland in 1950-1972 [20]. There are some differences between Statistical Yearbooks of Finland and this tobacco statistics [20], but before 1972 there is seen in general an increase and rapidly decrease after 1974. (Associated with efforts of The North Karelian Project). During smoking reduction proportion of female smokers of all smokers increased (1979-1991) from 33 to about 40 % [21], which could explain the stagnation in F.CHD between 1983 and 1987.

Soil-Plant-Associations: Mg alone has explained barley Mg variation only about 30 %, but together with other minerals ca 40 – 50 % [22] (from different fields). Obviously, in successive years from the same fields soil, Mg could better predict plant Mg. Soil Mg/Ca ratio has been reported to explain ca 70 % of timothy Mg/Ca variation [23]. It is obvious that annual Mg allowance of humans via the basic food increased in Finland between periods of 1966-1970 and 1986-1990.

Because Mg is a cofactor in more than 300 enzymatic reactions [24], several other mechanisms and associations than [7,8,9] even outside of cardiology can and could in future explain CHD. Begin of CHD decline in 1967, five years before the start of The North Karelia Project [25] and about seven years before begin of smoking decline [20] suggests on further discussion.

Conclusions

Magnesium status of Finnish agricultural soils associated inversely with human CHD in 1961-1990 and could be one causative
factor of the Finnish CHD epidemic.

Acknowledgements

We are grateful to veterinary surgeon Seppo Haaranen for several discussions.

 References

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2. Jokinen R. Requirements for Magnesium fertilization in Finland, Journal of the Scientific Agricultural Society in Finland. 1981, 53: 239-268.

3.Giannuzzi P, Wood DA. Eur J Cardiovasc Prev & Reh, 2007.

4. Shechter M, Sharir M, Labrador MJ, Forrester J, Silver B et al. Oral magnesium therapy improves endothelial function in patients with coronary artery disease. Circulation. 2000, 102(19): 2353-2358.

5.Jeppesen BB. Magnesium status in patients with acute myocardial infarction: a pilot study. Magnesium. 1986, 5(2): 95- 100.

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11.Age-adjusted total and coronary mortality (I20-I25) of men and women, 35-64 yrs, Finland 1969-2005.

12.Eurofins Viljavuuspalvelu Oy.

13. Kurki Martti. Suomen peltojen viljavuudesta II, Ca, Mg and K values per soil-type, and soil-type-distribution of whole, 1972.

14. Ca, Mg and K values per soil-type, and soil-type-distribution of the whole country. 1976-1980.

15. Average acidity and nutrient content of different soils by Rural Centers.

16. The law concerning the limitations on the use of agricultural soil, 216/1969.

17. Statistical Yearbook of Finland 1962.

18. FAOSTAT, 2014.

19.FAOSTAT, 2014.

20. Official Statistics of Finland. Tobacco statistics, 2009. 

21. Official Statistics of Finland. Tobacco statistics, 2009.

22. Jerlström H-G. Studier över möjligheterna att med växtoch jordanalyser beskriva magnesiumsituationen i svensk växtodling, 1975.

23. Toysa T. Agro-Geology and CHD in Finland. J J Agriculture. 2015, 1(1): 006.

24. Elin RJ. Magnesium: the fifth but forgotten electrolyte. Am J Clin Pathol. 1994, 102(5): 616-622.

25. Puska P, Vartiainen E, Laatikainen T, Jousilahti P, Paavola M. THE NORTH KARELIA PROJECT: FROM NORTH KARELIA TO NATIONAL ACTION, Helsinki 2009.

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