Sirtuins took their name from Sir2 (silent information regulator 2), NAD+ dependent histone deacetylase which has been shown to slow down replicative aging in yeast. Sirtuins may counteract at least six hallmarks of organismal aging: neurodegeneration, chronic but ineffective inflammatory response, metabolic syndrome, DNA damage, genome instability, and cancer incidence.
Caloric restriction boosts sirtuin activity, which raise NAD+ levels by stimulating NAD+ biosynthesis that leads to slow down of aging. That is why caloric restriction is sometimes practiced by some people for longevity purposes.
However, instead of caloric restriction, which is difficult to achieve by some people, consuming precursors of NAD+ like NMN has been shown to increase NAD+ levels in the blood as well.