Community screening for glucose intolerance in middle-aged Icelandic men. Deterioration to diabetes over a period of 71/2 years

A number of 2203 middle-aged Icelandic men (aged 34-61 years) participated in a health survey in Reykjavik in 1967-68. Blood glucose in the fasting state and during an oral glucose tolerance test (OGTT) showed a unimodal distribution with a slight skewness towards higher values. A positive age gradient was established, which showed an increment of about 7 mg/dl per decade in capillary blood sugar values at 11/2 hours after a 50 g oral glucose load. The age gradient was mostly independent of age-related changes in body weight. A 71/2 year followup of the eligible participants (response rate 80%) showed an overall 1% incidence of metabolic deterioration to "overt diabetes" during this period. Those with positive screening tests (50 g OFTT) at baseline were at greater risk of developing diabetes, but the incidence of deterioration in this group was low, about 1% per year. The progression to diabetes was significantly related to body weight at baseline, suggesting that weight reduction might be beneficial in individuals showing impaired glucose tolerance at medical examination. This study, however, lends support to recent reports showing that mildly impaired glucose tolerance cannot be equated with early diabetes.

Fasting and two-hour post-load glucose levels for the diagnosis of diabetes. The relationship between glucose levels and complications of diabetes in the Pima Indians

The frequency distributions of both the fasting and two-hour post-load plasma glucose levels were bimodal in the Pima Indian population aged 25 years and over. The hyperglycaemic component of this distribution represents those with diabetes mellitus, as some 30 percent of this group had evidence of the specific vascular complications of the disease, whereas these abnormalities were virtually absent in those with lower glucose levels. The bimodal characteristics of the frequency distributions were utilized to define optimal criteria to separate those with and without diabetes. The sensitivity and specificity of these criteria for fasting and two-hour glucose levels were compared and were found to be similar. The fasting glucose determination, however, was more reproducible and stable, as well as being easier to obtain, indicating that it is the better measurement for diagnostic purposes. The optimal level for diagnosis of 7.5 mmol/l (136 mg/dl) for the fasting glucose and the equivalent two-hour value of 14 mmol/l (250 mg/dl), were higher than many previously recommended diagnostic levels. Nevertheless, there was no evidence that subjects with lower levels were at appreciable risk of developing the specific complications of diabetes. Subjects with impaired glucose tolerance (IGT), but without fasting hyperglycaemia, should not be diagnosed as having diabetes mellitus.

The effect of aging on carbohydrate metabolism: a review of the English literature and a practical approach to the diagnosis of diabetes mellitus in the elderly

There seems little doubt that the disposal of a glucose load is progressively impaired during aging. The mechanism(s) for this alteration remains unclear. Five possibilities have been raised: (1) poor diet, (2) physical inactivity, (3) decreased lean body mass in which to store the carbohydrate load, (4) decreased insulin secretion, and (5) insulin antagonism. Although poor diet and physical inactivity may contribute to some of the abnormal glucose tolerance tests of the older population, these two factors do not provide a full explanation. Diminished lean body mass may play some role but there is almost certainly an additional effect due to aging. A few papers have suggested that glucose-induced insulin secretion may be impaired as the population ages, but the bulk of studies in this area conclude that normal or increased amounts of insulin are released by the pancreatic beta-cell during aging. If abnormalities of insulin secretion exist, either in degree or timing, they are subtle and would not seem sufficient to account for the great number of older subjects who manifest impaired glucose tolerance. The evidence for insulin antagonism seems the strongest but the data are certainly not conclusive. In actuality, the aging effect on carbohydrate metabolism may be heterogeneous in nature. Either some or all of these five factors may contribute to the aging effect to varying degrees in individual subjects. Alternatively, the glucose intolerance of aging may represent a heterogeneous group of disorders. In any event, until better methods to identify possible subgroups of these subjects and/or a marker for diabetes mellitus independent of glucose concentration become available, this problem will remain difficult to resolve. Based on the currently available data, it seems prudent to diagnose diabetes mellitus only if fasting hyperglycemia is present.

Long-term treatment of subjects with borderline glucose tolerance

Subjects with borderline glucose tolerance are at a higher risk of suffering and dying from cardiovascular disease than subjects with normal glucose tolerance. Our data on the progression to overt diabetes and our data on cardiovascular morbidity and mortality suggests that tolbutamide treatment reduces these risks. In any case, we have no data supporting the theory that tolbutamide promotes cardiovascular damage.

Worsening to diabetes in men with impaired glucose tolerance ("borderline diabetes")

Two hundred and four men with impaired glucose tolerance (borderline diabetes) discovered in a screening examination have been observed for five years and repeated tests of glucose tolerance performed. By pre-determined criteria 27 men 'worsened to diabetes' and this metabolic deterioration was not significantly influenced by treatment with carbohydrate restriction with or without a daily dose of 50 mg phenformin. Of the baseline variables measured prior to treatment allocation only the blood glucose values were significantly predictive of ultimate worsening to diabetes.