What it do before covid?
I'm not sure what you're asking here, but I'll try to answer. In the 1950s, niacin was found to be excellent for cholesterol management. In the 1960s, niacin was found to be a cure for some forms of schizophrenia. In the 1970s, niacin was found to be helpful in alcoholism. In the 1980s, a doctor wrote a book saying that if everyone got enough niacin, there would be no heart attacks. By the 1990s, statins -- with patent protection -- became the favored method of cholesterol control, and niacin was buried.
Research in the past decade has shown that though statins control cholesterol, they provide no benefit to longevity, and their side effects (muscle weakness, neuropathy) reduce quality of life.
Other recent research is showing that flush niacin is good for a variety of neurological problems, including Alzheimers and Parkinsons. Many neurological problems can be trace to the gut -- especially to the gut bacteria -- and niacin has the effect of normalizing gut bacteria, better than probiotics.