Breastfeeding has well-established immunity and developmental benefits for newborns, yet mothers of preterm infants often struggle to provide sufficient breast milk. The investigators hypothesize that supplementing mothers of preterm infants with nicotinamide riboside (NR) during early postpartum will result in increased milk production. NR is a unique precursor to NAD+, which functions in whole-body metabolism, including that which supports the elevated energy demands of lactation. In lactating rats, NR supplementation improved milk quantity and quality, with metabolic benefits for the mother and lasting protective advantages for the offspring. No studies have been conducted to date that explore the short- or long-term use of NR for increasing milk supply in lactating women. This study will follow a small cohort of women and very preterm infants in the NICU throughout two intervention phases-- one in which each mother will randomly receive either NR or a placebo, then the opposite treatment-- to determine the effect of maternal NR supplementation on expressed milk volume and other markers of metabolism.