What is the difference between NAD and NAD+?

NAD is often used as shorthand for NAD+. NADH is easier to manufacture, and was tested for various conditions 10 years ago, and is still available on Amazon. But recent research has shown it is the ratio of NAD+ to NADH in the cells that is important for health and longevity. Less NAD+ or more NADH is detrimental, so we sell NAD+. NR and NMN convert to NAD+ in the body.