Sir ,-Tradionaly the inhabitants of north-eastern Japan consumed 20-30 g of salt per day.1) In 1960 Dahl2) reviewed evidence that salt ingestion may be related to hypertension and reported epidemiological findings in human hypertension.2) From observation in north-eastern Japan, Sasaki3) suggested that interaction between genetic and environmental factors is important in the causation of human hypertension.3)

We have tried to asscess the changes in salt intake and blood-pressure in individual subjects over 20 years. The volunteers were　chosen from farming people in Oinomori and Kanaya villages, in the north-east.3) Their average age, both male and female, was 46. Three consecutive 24 h urine samples were collected from the same person in 1961 and 1981. Blood-pressure was measured once or twice a year by mass surveys from 1954 in Oinomori and from 1958 in Kanaya, respectively, up to 1975, and the changes in blood-pressure for each person were calculated from the records obtained during the entire period(see table). The salt intake of these farming people decreased from 17.0 g per day in 1961 to 11.9 g in 1981 and the blood-pressure did not rise with advancing age.

1) Sasaki N., High blood pressure and the salt intake of the Japanese. Jpn Heart J,1962;3:313-24.

2) Dahl L.K., Possible role of salt intake in the development of essential hypertension. In Bock KD, Cottier PT, eds. Essential hypertension. Berlin:Springer, 1960:53-65.

3) Sasaki N. Epidemiological studies on hypertension in Northeast Japan. In Kesteloot II, Joossens JV,eds. Epidemiolgy of arterial blood pressure. Hague: Martinus NIjhoff, 1980:367-77.

Villges　 No　NaCl(g/day)　 K(g/day)　 Na/K(mmol/mmol) Syst.BP(mmHg) Diast.BP(mmHg)

Oinomori 13　15.5→11.3 **　 1.8 → 1.7　　6.1 → 4.7* 　122 →121 　　 68→ 72

Kanaya　13　 18.6 →12.6**　 2.1 → 1.5 **　6.5 → 6.3　133 →131　　　77 → 75

Total　　26　 17.0 →11.9 *** 1.9 →1.6 *　　6.3 → 5.5*　127 → 126　　 73 → 75

*p<0.05 **p<p.01　***p<0　　　Students'paired comparing urine data　for 1961 and 1981