With regard to　the diseases of circulatory system in Japan, especially cerebrovascular diseases, it is of interest to compare the profile with that in other countries. Mortality rate of　cerebrovascular diseases is high, particularly in the northeast Japan. The mortality rate is significant in young people and middle age, just as it is in those over sixty years. The cause of death is mainly cerebral hemorrhage, and there are seasonal changes, e.g. it is high in winter and low in sumer. On the contrary, it has been recognized that mortality rate of coronary diseases is low. The pattern of death from cerebral and cardiac diseases has changed with time based on the results of descriptive or longitudinal epidemiological studies during the past 20 years in Japan. Here the author presents the epidemiological studies in Japan concerning the sodium intake.

STUDIES IN JAPAN

In our country, the sysytematic study of the cerebral apoplexy began in 1941. Kondo and Kato(4) who had studied the cause of apoplexy by "hygienic" approach, found that there were villages with relatively high incidences of stroke in young people below 50 years of age in Akita prefecture. They mentioned that the factors such as heredity, cold climate, drinking of local unrefined "sake", overeating of rice and excessive intake of salt, as being related to the death rate from stroke in Japan.

In 1952 Fukuda(3) studied the nature and the presence of hypertension and surveyed the quantity of salt intake was 26.3gm per day per person by measuring urinary Cl excreation of 293 farmers. Dahl(1), who was advised by Fukuda, studied the Japanese circumstances in 1958, and was so encouraged by the results as to explore actual salt intake among groups, in which the prevalence of hypertension was variable. Dahl(2) reported the evidence that salt ingestion may be related to hypertension based on the results of the epidemiological studies, including the data of Japan, at an international symposium of essential hypertension in 1960.

We have started epidemiological studies on stroke and hypertension in Japan, especially in the inhabitants of the northeast, in 1954. Takahashi et al.(11) reported that the geographic distribution of cerebral apoplexy and hypertension in Japan could be explained in part by the differences of atmospheric temperature. In addition, the areas where the cerebral apoplexy and hypertension　were frequent were villages in which there was a surplus intake of rice and salt and a lack of vegetables. We(5) reported that there was a significant positive relation the estimated total per capita salt intake of farmers, the salt intake of farmers, the intake from "miso" and the salt intake from pickles and other vegetables and middle age(30-59 years) death rate from cerebral apoplexy in 46 prefectures in Japan. The investigation also studies the relationship of potassium intake to high blood pressure. It was observed that the mortality from apoplexy and hypertension was comparatively low in the apple producing regions in the northeast suggesting apples containing abundant potassium may have something to do with this phenomenon. We found a low incidence of apoplexy and comparatively low blood pressure among a Japanese populations whose diet was high in sodium chloride and who were also eating also a high level of potassium in the form of fruit(6,7). We studied the beneficial effect of apple eating on hyperetension in a field trial(6,7).

Among many prospective epidemiological studies on apoplexy and hypertension in Japan.　Shigiya et al.(10) reported that where the salt intake was high, the incidence rate of cerebral apoplexy was high. In certain groups in Osaka where the indcidence rate of cerebral apoplexy and the prevalence rate of hypertension were low, salt intake was also low.

The author reported the working hypothesis on the differences in blood pressure in various populations in the world based on the relationship between the daily salt intake and the levels and distributions of the blood pressure at the meeting held at Minnesota University(8) and at the round table session entitled "Causative Factors in Hypertension," 6th World Congress of Cardiology, London, 1970.

NEW FINDINGS

After 1970 many papers concerning blood pressure and salt intake were presented from various parts of the world. Some of our new data are shown in the following figures.

Figure 1 and 2 Mean systolic blood pressure by age, sex, and average daily salt intakes in different areas and different races. Number refers to the groups listed in Table 1.

Table 1 Average daily salt in different geographic areas and among different races

No Region　Groups　Daily salt intake　　Reference

1 Brazil　Yanomamo　”No-salt”culture　Oliver　et al.(1975）Circulation,52:146

2　Brazil　Carajas　No table salt(plant asches) Lowenstein(1961） Lancet,1:389

3　Brazil　Mundrucus　Ｒegular use of table salt

4　New　Guinea　Highland　natives　Little or no salt（１．７gm）　White（1958):Aust.Ann.Med.,7/8:36

5 New Guinea Coastal natives Do not lack salt

6 Solomon islands Baegu 0.6-1.7 gm Page et al.(1974): Circulation,49:1132

7 Solomon islands Aita 0.6-1.7 gm

8 Solomon islands Kwaio Less than 1.2 gm

9 Solomon islands Nasio 2.9-7.5 gm

10 Solomon islands Nagovisi 2.9-7.5 gm

11 Solomon islands Lau 8.7-13.3 gm

12 South Pacific Pukapukans 2.9-4.1 gm Prio et al.(1968):New Engl.J.Med. 279:515

13 South Pacific Rartotonga 7.0-8.2 gm

14 India Agra 6-10 gm Marthur et al.(1963): Am.J.Cardiol.,11:61

15 South Wales Rhondda Fach 8 gm Mial and Oldham(1958): Clin.Sci.,17:409

16 West Indies St.Kittz Negro 10gm Schneckloth et al.(1962): Am.Heart J.,63:607

17 U.S.A. Framingham 10 gm Kagan et al.(1959):Hypertension,vol.VII,Am.Heart Assoc. 　

18 Bahamas Negro 10-301 gm Moser et al.(1959):Am.Heart Cardiol.,4:727

19 Japan Yao,Osaka 13 gm Shigiya et al:(1975)

20 Japan Kochi 18 gm

21 Japan Hirai,Gumma 22 gm

22 Japan Nagano 22.1 gm

23 Japan Akita 20 gm

24 Japan Northeast more than 20 gm Sasaki et al.(1962):Jpn.Heart J. 3:313

Figure 1 showed the mean level of systolic blood pressure by age and sex in various populations in which the salt intake of the population was actually measured(Table 1). The blood pressure level is already high in a younger age group in areas where salt intake is more than 10 gm per day for a person and the subsequent greater rise of blood pressure upon aging is noted in these areas.　In areas with salt intake of less than 5 gm, the blood pressyre is low at a younger age and no rise is noted with increasing age.

The author(9) reported the longitudinal epidemiological studies on hypeertension in three farm villages(Oinomori-population about 700, Kanaya-population 1400 in Aomoriprefecture and Nishime-population 5000 in Akita prefecture) in the northeastern parts of Japan at the meeting of the First Asian Pacific Symposium on Hypertension in 1976. Blood pressure was determined once or twice a year by mass survey from 1954, 1957, and 1958, respectively, up to 1975. The levels and distributions of blood pressure by age and sex in corresponded to the death rates from cerebrovascular diseses in the middle age in three areas. Intervention studies on hypertension control by reducing high salt intake have been carried out in N-village from 1957 and in K-village from 1958. The level of the blood pressure in the beginning in the late 1950s not only in the middle-age group but also in such a younger age group as secondary school children(Fig.3)

. We could observe changes in dietary patterns such as how frequently or how many bowls of "miso" soup were taken a day. The contents of salt in "miso" soup is 1.5% average and one bowl of Japanese "miso" soup is usually 150-180 cubic centimeters. The reduction in the number of bowls taken at one meal was observed. On the other hand, there were no changes in the pattern of drinking "sake" and smoking. Urinalysis of sodium and potassium indicated that mean Na/K molar ratio in the populations was about 6 and was decreased in recent years. Generally speaking, the blood pressure of regression analysis of longitudinal trends on individual blood pressures. We calculated the frequency distribution of blood pressure of blood pressure of the death cases and the annual death rate from cerebrovascular diseases according to the level of blood pressure for each birth cohort in three villages. Years of observation were used for calculating death rates in cohort study and especially the death rate from cerebrovascular diseases was analysed at every 10 mmHg level in the distribution of blood pressure.　According to the results obtained in this study it become obvious that a person whose blood pressure level was high from younger age was apt to have a fatal attack of stroke. The type of cerebrovascular diseses was mostly hemorrhagic in the middle-age group under sixty years although the population of cerebral hemorrhagic and cerebral infarction was half-and-half in the old age group. The propotion of ischemic heart disese among causes of death as a whole was very low in these population.

Now we are tring to investigate the sodium content in human hair as new index of salt intake over a long term. In one comparative study of the mineral content in human hair in Japan and New Gunea, we(Sasaki et al. unpublished data) found distinct differences in sodium and potassium contents(Table2).

Table 2 Mineral contents in human hair of the population in different geographic areas (Oriomo Papuans, New Guinea and Akita, Japan)

Subject Na(M+α) K Na/K Ca Mg Zn Method of washing

New Guinea 651+412 949+530 1.48+1.47 960+391 215+90 117+30 untreat

Japan 1138+854* 420+357** 6.00+4.37** 947+509 170+157 172+35**

New Guinea 6.8+5.0 16.6+10.1 0.68+0.20 603+278 118+53 110+25 washed with distilled water

Japan 49.2+55.9** 41.1+27.1** 1.85+1.36** 834+508 131+154 163+32**

New Guinea 2.4+0.68 5.8+1.6 0.74+0.21 394+100 75+26 99+27 washed with 10% acetic acid

Japan 7.5+7.1** 10.8+9.8* 1.35+0.75** 514+168* 57+32 141+27*

Number of samples:19 Na,K,Ca,Mg and Zn:μg/gm dried hair.Na/K:mEq *p<0.05 **p<0.01

The hair specimens were collected from two population which have different food habits: people from Oriomo Papuans, New Guinea have little salt and people from Akita, Japan have excess salt. Untreated hair and washed hair with distilled water or 10% acetic acid were submitted to the determination of Na, K, Ca, Mg and Zn contents. Significant difference were observed at Na, K and Zn content and Na/K ratio between the two. It is possible that the differences in Na, K, and Zn intake affects the contentm of these minerals.

REFERENCES

1 Dahl, L. K.(1960) Salt, fat and hypertension: The Japanese experiences. Nutr. Rev.18:97-99.

2 Dahl, L. K.(1960) Possible role of salt in the development of essential hypertension. In:Essential hypertension, edited by K. D. Bock and P. T. Cottier, pp.53-65. Springer-Verlag, Berlin.

3 Fukuda, T.(1954): On the hypertension of Akita farm village. Chiba Med. J., 29:490-502.　　　　　　　　　　　　　 .

4 Kondo, S. and Kato, K.(1948): Hygienic studies on causative factor in apoplexy. In Noikketsu(Cerebral Apoplexy), edited by C. Nishino, pp. 62-71. Maruzen, Tokyo.

5 Sasaki, N. et al.(1960) Jpn.J.Pub.Health, 7:1137-1143.

6 Sasaki, N. et al.(1959) Med. Bio. 51:103-105.

7 Sasaki, N.(1976) Jpn. Heart J., 3:313-324.

8 Sasaki, N.(1977) Jpn. Circ. J. 41:1139-1142.

10 Shigiya, R. et al.(1975) Ecological aspects of nutritional status as limiting factors of life expetancy of Japanese. In Physiological Adaptability and Nutritional Statuts of the Japanese. edited by K. Asahina and R. Shigiya, pp. 127-191. Univversity of Tokyo Press, Tokyo.

11 Takahashi, E. et al.(1957)The geographic distribution of cerebral hemorrhage and hypertesion in Japan. Human Bio., 29:139-166.