Does niacin supplementation in a dose of 500 mg/day have any impact in elevating testosterone levels in men? thank you.

Not great data: Evidence suggests higher doses of Niacin 1-3gm may lead to a growth hormone surge, but not so much testosterone. Remember as the dose of niacin increases so do the adverse effects like flushing. I would be very cautious about higher doses of Niacin for supplement purposes, but if your doctor feels it would benefit you from a cholesterol perspective, that's another story.