Niacin sends homocysteine levels high, too, which the liver has to detox. It uses methyl-donors to do that, b6,b9, and b12 help recycle the cysteine molecules. Homocysteine is considered a toxic molecule, though it's pretty much just blood shunting a toxin out to the liver.
Skin flushing is a perfect time to apply olive oil to the reddened skin, it helps! Niacin is one of the nutrients that triggers fat metabolisim.