Drinking alcoholic beverages can depress your fasting blood glucose levels. This can be beneficial, but it can also lead to a false sense of security about your glucose metabolism.
The ethanol in alcohol inhibits gluconeogenesis, which is the new (neo) making (genesis) of glucose (gluco). Gluconeogenesis occurs primarily in the liver and is one way your body supplies glucose to tissues during a fast, such as overnight.
So, if the only reading you're checking is fasting, or first thing in the morning, and it's below 100 mg/dl, and you think you're fine, double-check it with a few postprandials throughout the day. (A high HbA1c with low fastings could result from this effect.)
Here's one study:
Glycemic Effects Of Moderate Alcohol Intake Among Patients With Type 2 Diabetes: A Multicenter, Randomized, Clinical Intervention Trial, Diabetes Care, 2007
Participants (91 completed the study) had type 2 diabetes and received one of the following daily for 3 months (consumed at dinner):
- 150 ml wine (about 5 ounces or a little more than 1/2 cup) (either Merlot or Sauvignon Blanc)
- 150 ml nonalcoholic diet beer (control group)
- In the wine group, fasting glucose dropped from 139.6 to 118.0 mg/dl.
- The control group experienced no change, 136.7 to 138.6 mg/dl.
- Those with the highest HbA1c levels had the greatest reductions.
- Alcohol consumption had no effect on 2-hour postprandial glucose.
Update: For those who are asking: A normal (conservative) postprandial blood glucose reading is below 140 mg/dl. You want to see your blood sugar getting below 140 at about 2 hours after you finish eating a meal.