It is well known that the renal concentrating ability is greatly influenced by the amount of protein in diet, and, there are many reports that high protein diet enhances the renal concentrating ability and the low reduces it. This fact is of paramount importance in renal physiology of the Korean, because the majority of Korean people are living on low protein diet.
In earlier studies, Suh and Hong(1961) reported that the renal concentrating ability seems to be lowered in the Korean as compared to the occidental, which was attributed by them to the ingestion of a low-protein diet. Hong et al.(1961) further demonstrated that the osmotic composition of urine excreted by the Koreans is somewhat unique in that NaCl accounts for nearly 2/3 of the total urine osmolarity, suggesting that the slat intake is perhaps greater while the protein intake is less in the Korean than in the occidental.
While, it is also well known fact that herbivorous animals travel long distances to salt licks, thereby manifesting a salt craving whihc is not found in carnivorous animals. Meneely(1954) stated that the physiologic reason for the added salt requirment on a cereal-vegetable diet remains obsqure. Chasis and his colleagues (1950), and, Weston and his colleagues (1950) pointed out that the renal hemodynamics are reversed to normal, if sufficient amount of slat added to low-protein diet.
From this point of view, Kim(1963) speculated that the ancestors of Korean people acquired the habit of excessive salt intake to maintain a noraml renal hemodynamics as a compensatory mechanism for lowered hemodynamics on low-protein diet. In this
studies, Kim also demonstrated that the lowered renal concentrating ability is caused by the low protein diet while the greater intake of water and urinary flow are attributable to excessive salt intake.
Regardless of whether Kim's speculation is true or not, it is of considerable interest tos ee that how the excessive intake of salt in Korean people developed in various age group, geographic areas and different seasons.
Hence, in this investigation, twenty four hour urines were collected for the measurements of the volume, the osmolarity, sodium, chloride, potassium and total nitrogen. The subjects were 1,260 persons, which were randomly chosen in healthy persons from three different geographical areas (city, rural and island) in age from 6 to 25. The seasons were summer, fall, and winter. Among these subjects, blood studies were made in 225.
Results obtained may be summarized as follows;
1. Plasma concentrations of electrolytes(including protein) were within normal range in all groups.
2. Daily urinary output which increased as a function of age was somewhat greater in summer than in winter. However, daily urinary output per unit surface are decreased as a function of age.
3. Urine osmolarity which increased as a function of age was higher in winter than in summer.
4. Daily excretion of NaCl which increased as a function of age was greater in summer than in winter. However, daily excretion of NaCl per unit surface area was constant regardless of age.
5. Daily excretion of potassium which increased slightly as a function of age was greater in winter than in summer. However, daily excretion of potassium per unit surface area decreased as a function of age.
6. Urinary K/Na ratio which decreased as a function of age was higher in winter than in summer.
7. Daily excretion of nitrogen which increased as a function of age was much greater in winter than in summer. However, daily excretion of nitrogen per unit surface area decreased as a function of age.
8. There was no distinct geographic difference in the values of these variables.
9. Although the magnitudes of most of these variables changed as a function of age, they tended to stabilize at the age of approximately 15 years.
10. Quantitative comparisons indicated that daily urinary output and NaCl excretion are greater while urine osmolarity, daily nitrogen excretion and urinary K/Na ratio are significantly lower in the Korean than in the occidental.
11. These results strongly suggest that Korean people acquired a habit of ingesting low-protein and high-salt diet at the age of 6 years or perhaps before, and also that the renal concentrating ability is fully developed at the age of approximately 15 years.