The extent of a focal tendon abnormality was intrasubstance in none (0%) of 16 patients with full-thickness tears, one (20%) of five patients with bursal surface partial-thickness tears, two (20%) of 10 patients with articular surface partial-thickness tears, and two (15%) of 13 patients with tendons without tear.
1 Adequate Intake (AI), where no RDA has been established, but the amount established is somewhat less firmly believed to be adequate for everyone in the demographic group.  Tolerable upper intake levels (UL), to caution against excessive intake of nutrients (like vitamin A) that can be harmful in large amounts.
Everyone needs a certain amount of niacin -- from food or supplements -- for the body to function normally. This amount is called the dietary reference intake (DRI), a term that is replacing the older and more familiar RDA (recommended daily allowance). For niacin, the DRIs vary with age and other factors.