Alcohol consumption alters insulin secretion and cardiac autonomic activity

BACKGROUND: Alcohol may have a cardioprotective effect. One possible mechanism is by modifying insulin resistance/secretion. The aims of this study were: (i) to examine the effect of short-term alcohol consumption on the metabolic control of glucose tolerance; (ii) to study the influence of short-term alcohol consumption on cardiac autonomic activity using spectral analysis of heart rate variability. METHODS: Twenty-one healthy subjects, in a randomized crossover design, either received three units of ethanol daily for 1 week or abstained from ethanol. The control of glucose tolerance was assessed using the intravenous glucose tolerance test with minimal modelling. RESULTS: There was no difference in fasting glucose, fasting insulin or insulin sensitivity between the two groups. Alcohol showed a lower insulin first phase insulin response (no alcohol 659.0 +/- 394.1 SD, alcohol 535.2 +/- 309.1) pmol L-1 min-1, P = 0.027). There was no difference in heart rate or blood pressure but a significant difference in the ratio of high to low frequency spectral power of heart rate variability; (no alcohol 4.55 +/- 3.78, alcohol 8.16 +/- 6.77, P = 0.033). This suggests decreased sympathetic and/or increased vagal modulation of heart rate in the alcohol group. CONCLUSION: The finding of no difference in insulin sensitivity between the two groups contrasts with, but does not entirely contradict, the results of previous epidemiological studies--perhaps suggesting that longer term changes such as liver enzyme induction may be important. The difference in insulin secretion questions the validity of previous studies of the influence of alcohol on insulin sensitivity, where insulin levels were used as a surrogate for insulin resistance.