SHR # 2364 :: What Is The Reason For The Decline in NAD plus As We Age? : Joel Greene - If you believe the science that declining levels of Nicotinamide Riboside is the reason for advanced aging, then is't the logical question "why dose it decline?" No one in the NAD plus space seems to ever explain that. CD38 would be the answer. So, if CD38 is causing the decline in NAD+ why aren't we focusing on that?