Glucose tolerance and smoking: a population study of oral and intravenous glucose tolerance tests in middle-aged men.

The oral and intravenous glucose tolerance tests have been compared in middle-aged, normal-weight male non-smokers, ex-smokers and smokers who participated in a general health screening programme in Malmö, Sweden. Subjects with diabetes, previous gastric resection and/or present medication with diuretic agents were excluded. No difference was found when comparing fasting glucose in non-smokers, ex-smokers and smokers. In the oral glucose tolerance test, plasma glucose at 40 and 60 min increased stepwise from non-smokers (8.7 and 7.4 mmol/l) to ex-smokers (8.9 and 7.5 mmol/l), smokers (9.2 and 7.9 mmol/l) and heavy smokers (9.7 and 8.2 mmol/l). Blood glucose levels at 120 min were inversely arranged. Plasma insulin at 120 min was lower in heavy smokers (16.2 mU/l) than in non-smokers (24.8 mU/l). The mean intravenous glucose tolerance test k-value was lower in smokers than in non-smokers. K-values below 1.0 were twice as common in smokers (30%) as in non-smokers. It is concluded that smoking has a clinically significant influence on both the oral and intravenous glucose tolerance tests.