The study on the kynurenine pathway is very interesting in context. Whether niacin is a key vitamin and plays a role here is plausible. As with anything involving the metabolism, it's also plausible that the overall effect is a result of a recipe comprising multiple key ingredients depending on one another. Good stuff!

This is also consistent with recent finding of how changes at the cellular level can turn on and off genetic influence. Epigenetics is starting to uncover how our environment can directly influence our health and overcome genetic predisposition, or not, depending on what's in our environment. Dietary consumption and the microbiome is a part of our environment.