First, it must be said that someone with diabetes should ALWAYS check with their doctor and be sure to monitor their blood glucose (BG) levels very carefully when adding new things to their diet.

That said, you can click on the sentence/link below for this video that's a great answer about how wine affects diabetes and blood sugar levels.

LINK: How do wine and beer affect my blood sugar level?

An important quote from the video is this:

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"It's got sugar alcohol, which doesn't raise blood sugar levels, so a glass of wine can lower your blood sugar levels."
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I think the key here is moderation and the type of diabetes one has. Someone who is Type I insulin dependent diabetes might see a greater or lesser change in BG than someone who is Type II adult onset diabetes. It would appear that a glass of wine with dinner when BG is moderate to low won't hurt anything, but it's likely you'll want to avoid anything that can alter BG negatively when it's super low or super high.

White wine has a glycemic index of 0, meaning it has no digestible carbohydrates, and therefore would have almost no effect on blood sugar levels.

Red wine, on the other hand, has actually been shown in recent studies to possibly help lower blood sugar in type II diabetics. This article gives more information about that:

http://www.newswise.com/articles/view/539273/

So it would seem that wine, when it is drank in moderation, can have positive aspects for diabetics.

Some more helpful links below: