good news re liver tests even if they're not the most reliable indicators in the world. still it's known that niacin can be hepatotoxic so best to monitor using what's available.
as for zinc, sounds like the range is off at your lab. it's a pretty common issue. to clarify, the WHO 'normal' range (which includes both sick and healthy people) is 11.5-18.5 umol/L (75-121 ug/dL). meanwhile at an infectious disease clinic I've dealt with, where you'd expect all the data points to be from pretty unhealthy individuals, the 'normal' range for serum zinc is 9-14 umol/L (59-92 ug/dL).
your zinc test came back 80, so according to the infectious disease clinic's range, you're smack in the middle of 'normal'. but as far as the WHO is concerned, you're at the bottom of the barrel. to match healthy controls you'd need to match more like 120.
optimizing zinc has good potential to help with the lipid profile, but adding the exercise is definitely a win!
while the flush may be a side effect of your cholesterol treatment, it is nonetheless an indicator. if you're not getting a flush reaction at 500mg intakes, i'd take that as a sign that there's something that needs work in the biochem department.
I already posted the zinc link, here's something on the fatty acid aspect:
Membrane fatty acids, niacin flushing and clinical parametershttp://www.sciencedirect.com/science/ar ... 7896901398
The results of this study of niacin flushing confirm that the absence of flushing is significantly associated with low levels of arachidonic acid and DHA.