Diurnal Variations in Serum Glucose, Insulin and C-Peptide of Normal Korean Adults

정상(正常) 한국인(韓國人) 혈청(血淸) 포도당(葡萄糖), Insulin 및 C-Peptide의 일중(日中) 변동(變動)에 관(關)한 연구(硏究)

It is already well known that many factors are involved in maintaining normal blood glucose level. The amount and components of meal are also thought to be some of the factors which affect the blood glucose and insulin levels. It is reported that as for Koreans sugar takes up over 75% out of 2,098 kcal, the average daily calorie intake per adult. It implies that Koreans take a high-sugar diet compared with Westerners who take $40\sim50%$ of sugar out of their total average daily calorie. For the purpose of studying diurnal variations in serum glucose, insulin and C-peptide of normal Korean adults based on ordinary Korean diet, we selceted 13 normal Korean male adults and divided them into two groups, Group I (7 persons) and Group II (6 persons). We put Group I on 3,100kcal and 75% sugar diet, and Group II on 2,100 kcal and 69% sugar diet per day for over 4 days. Serum glucose, insulin and C-peptide were checked every 30 minutes or every hour throughout 24 hours. Results are as follows: 1. As for serum glucose level, in the prep ran dial fasting state in the morning, $mean{\pm}S.D.$ of Group I was $91.1{\pm}8.2mg%$, while that of Group II is $82.5{\pm}4.4mg%$. Both groups showed peaks of increased glucose level at postprandial 1 hour after each meal. The peak returned to the level shown during the fasting state at postprandial 1 hour after breakfast while the relatively high glucose levels were maintained respectively even for 2 or 3 hours.after lunch and dinner. 2. As for serum insulin level, Group showed $mean{\pm}S.D.$ of $14.7{\pm}3.0{\mu}U/ml$ while Group II shows that of $7.0{\pm}2.6{\mu}U/ml$ in the fasting state. Group I particularly showed the largest peak from preprandial a half or one and half an hour to postprandial one hour of lunch, and made relatively small peaks $(47.7{\pm}10.8{\mu}U/ml)$ at postorandial 1 hour after breakfast and dinner. No such large peak was marked in Group II, though it showed relatively similar patterns of peak after each meal. 3. As for C-peptide, in the fasting state, Group I and Group II showed $3.50{\pm}1.85$ and $1.66{\pm}0.53ng/ml$ of $mean{\pm}S.D.$, respectively. Group II showed peaks parallel to those for insulin level. None out of seven in Group I showed expected increase in C-peptide based insulin secretion at a half or one and half an hour before lunch. On the contrary, C-peptide increased in 5 subjects out of seven in Group I at 11:00 p.m. when insulin did not increase. 4. According to the integrated concentration method for a measurement of 24-hour total. insulin secretion rate, the $mean{\pm}S.D.$ of Group I was $76.4{\pm}15.2$ U and that of Group II was $58.6{\pm}21.1$ U. The above results confirm that Koreans, when given ordinary diet of 2,100 kcal and 69%, sugar, show insulin secretion pattern essentially similar to that of Westerners. On the contrary, when they are put on a high-calorie diet of 3,100 kcal a day, 75% of which is sugar, insulin secretion can be increased before lunch without increase in blood glucose. These results implies that insulin secretion can be affected by some other factors. The observation that an increase in C-peptide after 11 : 00 p.m. independent of insulin level supports an assertion that insulin secretion and C-peptide secretion can be thought as being physiologically dissociable, and these changes of diurnal patterns in the levels of serum insulin and C-peptide are thought to be resulted from the large meal and high-carbohydrate diet.