Ascorbic Acid and Carbohydrate Metabolism. I. The Cortisone Glucose Tolerance Test

Abstract

Over the past quarter of a century, evidence has been accumulating from studies on lower animals (1-8) and humans (9-14) that there is a significant relationship between vitamin C and carbohydrate metabolism. Representative of published data is the observation that a progressive and significant decrease in glucose tolerance parallels the successive stages of vitamin-C depletion in guinea-pigs (1-2) (Fig. 1).The purpose of this report is to investigate whether in the human organism, a significant parallelism exists between cortisone glucose tolerance values and plasma ascorbic acid concentration. MATERIAL AND METHODSOne hundred and sixty-nine presumably healthy persons, drawn at random, participated in this experiment. The age and sex distributions are summarized in Table 1.Most of the subjects were in the third age decade and the sample was predominantly female. Carbohydrate metabolism was studied in each subject by means of the cortisone gIucose tolerance test (15). The plasma vitamin-C level was measured simultaneously under fasting conditions by the Mindlin-Butler technique (16). Figure 2 portrays the cortisone glucose tolerance pattern for the entire sample of 169 subjects. Three points are worthy of mention: 1) the mean values were well within the excepted physiologic limits, 2) the spread about the mean was least under fasting conditions (s.D. = 14.7) RESULTS Table 2 summarizes andand most a t one hour (s.D. = 44.4), and 3) on the basis of these means and standard deviations, it seems that some of the participants were prediabetic and others diabetic. Table 3 summarizes the plasma ascorbic-acid distribution for the entire group. There is still considerable controversy as to the physiologic range. The Interdepartmental Committee on Nutrition for National Defense (ICNND) argues that plasma ascorbic acid levels below 0.2 mg per 100 ml are unsatisfac- tory (17-19). If one accepts this cut-off point, then one most conclude from this survey that in 30.2 per cent of the participants the levels were too low. A few observers (20) prefer to regard 0.5 mg per 100 ml as the minimal acceptable level. On this basis, 55.0 per cent of the subjects in this survey had abnormal plasma concentrations. The majority of investigators favor a lower limit of 0.6