Copied from Earth Clinic:
06/19/2006: Ted from Bangkok, Thailand writes: "It has been known in academic circles for sometime that vitamin B3 in the form of niacinamide (non-flushing) is relatively toxic to yeast. A scientist found several years ago and concluded (wrongly) that taking vitamin B3 niacinamide will shorten your life span or longevity, through suppressing the SIR2 silencing gene, which is responsible for longevity.
As a result of this little misinformation, people stopped taking niacinamide and candida and yeast infections skyrocketed. Now the reason for the mistake was relatively simple, the scientist was apparently doing a study on longevity on yeast cells. Apparently in higher animals, fruit flies included, the effect of adding niacinamide resulted in longer life of 15%, as well as human embryo cells.
Therefore, if you have candida, yeast infection, or possibly even a UTI (urinary tract infection), taking niacinamide between 100-500 mg/day could solve this mystery that doctors have a hard time suppressing. In fact, you can expand this idea into applying the use of niacinamide NOT NIACIN, as a means of controlling fungus, since fungus is a relatively close cousin of the yeast also.
This is interesting, since in medicine the two most hardest organism to kill is actually fungus and yeast. It is almost a death sentence if you have this and getting rid of it may mean endless nightmare. Who knows, perhaps dissolving niacinamide with vinegar will be helpful in relieving your toe nail fungus infections.
Therefore a possibility exists from the point of view of biological terrain, candida, yeast and fungus infection is a form of niacinamide deficiency."
Seems this "Ted from Bangkok" is a pretty well informed guy. Note that he wrote this back in 2006, long before this recent research has confirmed his claims.