I'm sure your doc know what he/she's doing, but just to throw it out there - too much niacin (through supplementation, nearly impossible to do this on food alone) have adverse side effects, particularly with the nicotinic acid (the "flushing" variety.)
According to a report by the Oregon State University - 500mg/day of nicotinic acid for two months have led to hepatitis, and that substance at high doses has been linked to liver damage, impaired glucose tolerance & blurred vision.
Nicotinamide (the "non-flushing" kind) is generally better tolerated by the system, though at very high doses (2-3g/day) it causes similar adverse effects.
Link:
http://lpi.oregonstate.edu/infocenter/vitamins/niacin/