COVID AND THE VACCINE - TRUTH, LIES, AND MISCONCEPTIONS REVEALED, page-3879

It is a co enzyme and is made in the body from precursors, all forms of vitamin B3: nicotinic acid, nicotinamide (aka niacinamide), and nicotinamide riboside (NR).

The book 'Lifespan" by David Sinclair goes into it in some detail.

This is the one I take - developed by some Biochemists from Sydney Uni
https://biogency.com.au/product/synext/

I contracted Chronic Fatigue in my 20s and really didnt have much energy/resilience. Much better these days after changing diet, fasting and using targeted supplementation. The added benefit is a better immune system. My bloods are proof of that