I take almost 3 grams a day and my fasting (at least 12 hours) glucose
lab results lately have been low 70s to low 80s.  I don't think I see a
down side to Niacin in the glucose arena.  On the other hand,
homocysteine gets knocked up 1-2 points.

Joe

I assume you had fasting blood glucose
levels below 100 mg/dL before the niacin.

If so, I have noticed the same problem as you:
I get an increase in fasting blood glucose when
I take high doses of niacin or its relations.
It appears to be a known side effect for some
of us, but not all.

I am dropping my niacin dose so as to get back
below 100 mg/dL  fasting blood glucose.  Another
possibility is going on a low carbohydrate diet to try and
lower your blood glucose despite the niacin.

But it may be a tossup as to whether the beneficial
change in cholesterol you get from the niacin is
worth the harmful change in blood glucose.
The tradeoff may depend on your genes:  if you have
a family history of heart disease vs. a family
history of diabetes.

You might want to buy a home glucose
test kit so that you can easily track it.
In the USA, the kits go on sale at pharmacies
for about $10 including some strips/lancets, and
you can buy extra strips inexpensively on eBay.

Dave