Try and understand that a person is diabetic when there is excess sugar or glucose in blood. This may be due to wrong eating or lack of physical excercise. Wines are fermented grapes so as such very high in sugar content. When a diabetic person is taking them the glucose level already high would reach alarming levels.This is going to affect your eyes, kidneys etc.Read this article to understand.http://www.skinsheen.com/article-how-to-lower-your-risk-of-diabeties-431.aspx

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:

Wine increases your glycemic index due to its sugar content.

www.blog.wineeducation.com says:
"The good news for red wine lovers is that most dry red wines have little to no sugar (that being the meaning of dry). White wines are much more likely to have some sugar."
"Considering the health benefits of red wine, many diabetics, myself included, consider that a moderate amount of red wine is down right good for us. Most of the expert sources reluctantly agree. If you test, and red wine does not seem to be effecting your GI, than a glass or two with a meal may be for you."