There is nothing about antioxidants in general that affect lipoprotein levels. Niacin undoubtedly does have significant action on blood lipids so undoubtedly is more than an antioxidant. I find that interesting. Why should that be? Many biological processes act through receptors. The niacin effect on lipids, and the niacin flush (ever tried this? It's fun fun fun, not!), are receptor mediated. Clever people have found at least a couple of receptors. The first was HM74, now joined by HM74A. These receptors were not sitting there waiting for either psychiatrists or cardiologists to prescribe multigram doses of nicain, useful though that may be.
No, they have a natural ligand, beta hydroxybutyrate. Beta hydroxybutyrate is a substance dear to my heart, and your heart too, see here. It's a ketone body, naturally manufactured by the liver in times of starvation or carbohydrate restriction. Plus times of coconut fat consumption too, as medium chain triglycerides (MCTs) will produce ketone bodies even in the presence of carbohydrate. By the way, this is not my preferred fat, and it worries me a little that humans break down MCTs as fast as the liver can do so, plus they are shunted down the hepatic vein rather than the thoracic duct, minimising their access to the general circulation. It just reminds me of our metabolism's approach to fructose a bit. Still, coconuts have an excellent track record as a human food in the tropics, so I'm probably just being a bit paranoid here.
Low carbohydrate diets naturally produce ketone bodies. They will certainly elevate HDL cholesterol levels too. To which you may ask, "so what?". Well, elevated HDL cholesterol appears to be a marker of a high fat, low carbohydrate diet and its associated beta hydroxybutyrate. So it is a marker of good things happening in the metabolism. As such I welcome it, but not if it is an effect of some drug. Of course if your primary protection against heart disease is normal blood sugars and low insulin levels the elevated HDL-C is not essential, as seen on Kitava. On western food supply a little exercise plus LC eating seems to be the easiest way to maintain normal blood sugars, and coincidentally elevated beta hydroxybutyrate and so HDL-C. Statins and niacin may elevate HDL cholesterol but my guess is that their benefits (however small from the statins) are unrelated to their effect on HDL-C. And of course, once you are on a drug to elevate HDL-C, there is no way of telling if your metabolism is doing well or badly in terms of insulin sensitivity. If you combine a statin plus niacin plus the dreaded AHA Coco Krispies based low fat diet, you may well be on the road to a cardiovascular disaster, despite having the appearence of a "good" "good" cholesterol level...