This new article on Medscape shines a small amount of light on the subject you might have to signup to read so I will paste Some highlights here.
Drinking coffee might help prevent type 2 diabetes, according to a newly updated collection of studies compiled by the Institute for Scientific Information on Coffee (ISIC). But as ever, the devil lies in the details, with 2 experts disagreeing as to the exact conclusions that can be drawn from this work.
"The truth is, they can't show that drinking coffee reduces the risk for developing diabetes; all they can show is that there's a correlation," he told Medscape Medical News.
One theory is simple calorie replacement: Choosing coffee over sugary drinks leads to reduced calorie consumption, and coffee also speeds up the metabolism.
And there may be ingredients in coffee — apart from caffeine — with beneficial effects. According to the ISIC report, coffee contains components with potential anti-inflammatory, antioxidant, and hormonal properties that could improve insulin sensitivity. Other coffee ingredients could chelate iron, which also may improve insulin sensitivity or cardiovascular health.
Dr. Lane said his findings apply to all sources of caffeine, not just coffee. Caffeine raises levels of epinephrine (adrenaline), which also are known to stimulate the liver to produce glucose in a "fight-or-flight" response.
"We know caffeine has certain effects. It raises epinephrine and blood pressure. It can make you jittery and sweaty. For some people that's bad, for others it's just an annoyance… I would say people who have type 2 diabetes would be better off if they didn't drink coffee."
Dr. Lane's own work has shown a consistent acute worsening of glycemia with caffeine consumption. Most recently, in a small pilot study, he showed that 3 months of total caffeine abstinence improved glycemic parameters among 12 established coffee drinkers with type 2 diabetes (J Caffeine Res. 2012;2: 45-47). "Here, all they did was quit taking in caffeine, and their A1c improved as much as if they were taking in another medication," he told Medscape Medical News.
And in a prior review article, Dr. Lane cites 17 studies finding that caffeine exaggerates the rise in glucose after carbohydrate ingestion even in healthy, nondiabetic adults (J Caffeine Res. 2011;1:23-28 ).
Dr. Lane told Medscape Medical News that he has had difficulty obtaining grants to further his research. "Critics say it's not worth funding because you can't get people to stop drinking coffee, which we actually did in the pilot study... Even scientists reviewing research grants seem to love their coffee so much they don't want to see research against it."
For further information I suggest you read the references given in the article. Or alternatively Dr. Lane's original article.
It might be worth a try to see if reducing your caffeine ingestion will help with your blood sugar.
Personally as a type 1 I am usually successful at keeping my caffeinated beverages to 1 or 2 a day any more and I become too jittery to function well.
Also you might find this article "Chocolate consumption and Nobel Prizes: A bizarre juxtaposition if... interesting as it illustrates why correlation does not imply causation.