In mice, a vitamin-like substance called nicotinamide and its cousin NR get sent into bile after being injected, travel to the gut, get changed into another form by gut bacteria, and then help the liver make an important energy molecule—cutting off the bile stops this process.

What we've found so far suggests that in mice, bile may play a role in recycling forms of vitamin B3, such as nicotinamide (NAM) and nicotinamide riboside (NR), through a gut-liver cycle [1]. Our analysis of the available research shows that when these compounds are introduced into the body, they appear in bile, move into the gut, and are modified by gut bacteria before being reused by the liver to help produce an important energy-carrying molecule [1]. The evidence we've reviewed leans toward the idea that this recycling process depends on bile flow—when bile is blocked, the cycle is disrupted [1]. This suggests bile could be a key pathway for shuttling NAM and NR between the liver and gut, where bacteria help convert them into usable forms [1]. So far, we’ve analyzed one assertion from the scientific literature, and it supports this process in mice [1]. No studies we’ve reviewed have refuted it. However, our current analysis is based on limited evidence—only one key observation has been reported, even if it’s strongly supported within that context. We don’t yet know how much this process contributes to overall vitamin B3 levels or energy metabolism in mice, nor whether it happens in humans. Also, we can’t say whether other pathways might compensate if bile is blocked. Since all the evidence comes from studies in mice, we must be cautious about drawing broader conclusions. The practical takeaway: In mice, bile seems to help move certain vitamin B3 precursors from the liver to the gut, where bacteria may help recycle them for reuse. This suggests the gut and liver might work together to manage B3-related compounds—but we’re still early in understanding how this fits into the bigger picture of nutrient recycling.