Children at risk of Type-I diabetes are injected with its derivative to protect beta cells from decay, while its non-derived form has been used to reduce LDL levels.  
Deficiency of this substance can sometimes result from Hartnup's Disease and Carcinoid syndrome, the latter of which occurs because tumors cause tryptophan to be used to create serotonin rather than this vitamin.  Children at risk of Type-I diabetes are injected with its derivative to protect beta cells from decay, while its non-derived form has been used to reduce LDL levels.  A more typical deficiency of this vitamin comes from diets reliant primarily on maize, an affliction known as pellagra, and its derivative is primarily used in the body to form coenzymes NADP and NAD.  For 10 points, name this substance also known as Vitamin B3.
Deficiency of this substance can sometimes result from Hartnup's Disease and Carcinoid syndrome, the latter of which occurs because tumors cause tryptophan to be used to create serotonin rather than this vitamin.  
Niacin [or Nicotinic Acid; accept Vitamin B3 before mentioned]