Why is Niacin (Vitamin B3) so important for skin health?

Niacin plays an essential metabolic role throughout the animal kingdom. It is the precursor of important cellular coenzymes such as NAD e NADP, essential for energetic metabolism of skin cells and skin barrier integrity; it is needed for red blood cell formation, increased transport of oxygen and nutrients, removal of toxins & cellular waste products through skin microcirculation; it reduces triglycerides and cholesterol levels, prevents cardiovascular diseases, helps maintain healthy nervous system functioning and brain activity (its deficiency may cause serious mental illnesses); it plays a key role in synthesis of sex hormones estrogen, progesterone, and testosterone, etc.