The potential benefits of niacin (vitamin B3) in glaucoma have been under investigation in recent years. Oral niacin is protective against glaucoma in animal models,1 and an IOP-independent association between niacin intake and decreased risk of open-angle glaucoma has been observed by Jung et al. in a Korean population.2
Yee et al. build on this work in a cross-sectional study examining the association between dietary niacin intake and glaucoma risk in the 2005-2008 US National Health and Nutrition Examination Survey (NHANES) population. Dietary niacin was measured using two 24-hour recall surveys with post-survey dietary interviews, while glaucoma was ascertained using regraded disc images using the Wilmer criteria. The study also measured and adjusted for a variety of confounding factors.
Each one-mg increase in daily niacin intake was associated with a 6% lower glaucoma odds (OR 0.94, 95% CI: 0.90, 0.98) in the maximally adjusted model. However, a significant association was not observed in the model adjusted only for age, sex, and ethnicity. Moreover, there was not even a trend towards an association when examining niacin in quartiles. This lack of robustness of the association to different analytical approaches raises the possibility of a chance finding. It is possible the analysis examining niacin intake as a continuous variable was susceptible to leverage by outliers. While there was a suggestion that the association was only apparent in women, there was no significant interaction with sex, suggesting this may also be due to chance.
Limitations of the study include recall bias and the assumption that niacin intake during the observed period accurately represented long-term intake. Nutritional supplements and dietary tryptophan (which is endogenously converted to an active form of niacin) were not accounted for. Glaucoma diagnosis was limited to disc images. It is notable that the authors only examined 'definite' glaucoma, which had a low prevalence and could therefore result in unstable statistical results. If this association was also apparent for 'probable' glaucoma, it may increase our confidence that this is not a chance finding.
Despite the limitations, this study adds to the growing body of evidence supporting a protective effect of dietary niacin on glaucoma risk
Despite the limitations, this study adds to the growing body of evidence supporting a protective effect of dietary niacin on glaucoma risk. We eagerly await the results of the multiple randomized-control trials examining niacin in glaucoma patients currently in progress. A well-tolerated oral therapy that is complementary to currently available glaucoma therapies would be strongly welcomed.