Hyperinsulinaemia, obesity, and syndrome X.
OBJECTIVE: The major aim of this study was to compare various aspects of carbohydrate, insulin, and lipoprotein metabolism, serum uric acid concentration, and blood pressure in normal subjects stratified on the basis of both plasma insulin concentration and degree of obesity. The hypothesis to be tested was that hyperinsulinaemia, per se, was associated with relative glucose intolerance, higher triglyceride and uric acid concentrations, lower high-density lipoprotein cholesterol concentration and higher blood pressure, irrespective of degree of obesity. DESIGN: This represents a case-control study, in which normal volunteers were subdivided into four equal groups based upon degree of obesity and plasma insulin response to a 74 g oral glucose challenge. SETTING: The study was performed in the out-patient clinic of a university hospital. SUBJECTS: Sixty-four individuals were recruited for this study, subdivided into four groups based upon their plasma insulin concentration and body mass index. Subjects were classified as hyperinsulinaemic if their plasma insulin concentrations in response to an oral glucose challenge were more than two standard deviations above the mean of 732 volunteers previously studied [1]. Obesity was defined as a body mass index of > 30 kg m-2, and individuals were classified as non-obese if their body mass index was < 27.0 kg m-2. Based upon these criteria, four experimental groups were created: (i) non-obese hyperinsulinaemic (NOB hyper); (ii) obese hyperinsulinaemic (OB hyper); (iii) non-obese normoinsulinaemic (NOB normo); and (iv) obese normoinsulinaemic (OB normo). MAIN OUTCOME MEASURES: Subject groups were compared on the basis of the integrated plasma glucose response to a 75 g oral glucose challenge, fasting plasma triglyceride, cholesterol, high-density lipoprotein cholesterol, and uric acid concentrations, and blood pressure. RESULTS: Mean (+/- standard error of the mean) integrated plasma glucose response area for 2 h following a 75 g oral glucose load was significantly higher (13.4 +/- 0.4 vs. 11.0 +/- 0.4 mmol l-1, P < 0.001) in the hyperinsulinaemic group, as were the fasting triglyceride levels (2.4 +/- 0.2 vs. 1.4 +/- 0.1 mmol l-1, P < 0.001) and uric acid (5.3 +/- 0.2 vs. 4.4 +/- 0.2 mmol l-1, P < 0.05) concentrations. In contrast, high-density lipoprotein concentrations were lower in the hyperinsulinaemic group (1.06.0.05 vs. 1.32 +/- 0.05 mmol l-1, P < 0.001). In addition, blood pressure was higher in the hyperinsulinaemic group (136 +/- 5/87 +/- 2 vs. 123 +/- 2/82 +/- 1 mmHg, P < 0.05). Furthermore, when each of the two groups were divided into obese (n = 16) and non-obese (n = 16) groups, all of the differences outlined above persisted. These changes were independent of age, gender distribution, generalized and abdominal obesity, cigarette smoking, and estimated physical activity. CONCLUSIONS: The cluster of changes subsumed under the heading of syndrome X are closely associated with hyperinsulinaemia (and presumably insulin resistance), and can be discerned irrespective of degree of obesity.