Commentary on “Relationship between dietary niacin intake and erectile dysfunction: a population-based study”

The real benefits of vitamins and dietary supplementation on health outcomes have always been mired in controversy, and to date, contradictory studies continue to be published to highlight their benefits when downplaying possible adverse effects.1 This recently published National Health and Nutrition Examination Survey (NHANES) database study population investigating the role of niacin on erectile function reported that higher niacin intake, specifically in the highest tertile, was associated with a decreased risk of erectile dysfunction (ED) compared to the lowest tertile, showing an odds ratio (OR) of 0.56 (95% confidence interval [CI]: 0.37–0.85) based on 863 participants with ED from a pool of 3184 adults.2 Further analysis of dose–response curves and interaction analyses found a negative correlation between dietary niacin intake and the risk of ED, suggesting that a higher dietary niacin intake is associated with a reduced risk of ED.

Outcomes from the national registry and population-based studies should always be interpreted with caution. For a start, this registry was never designed to provide a causal-effect relationship between dietary niacin intake and the development of ED despite this article being an epidemiological cross-sectional study. The lack of actual serum niacin level measurement and standardized protocol in the intake of niacin limits the extrapolation of actual clinical findings. Similarly, the absence of oxidative stress and inflammatory markers of niacin means that the actual clinical effects on lipid metabolism and vascular endothelial function related to niacin intake are unknown. Moreover, the diagnosis of ED is largely based on a questionnaire format rather than an objective penile duplex ultrasonography. The relatively short-term data of 3 years from 2001 to 2004 also restrict the generalization of this study’s findings to the current population.

Niacin, also known as nicotinic acid or vitamin B3, is a water-soluble B vitamin found naturally in some foods, added to foods, and sold as a supplement. It is believed that niacin has antioxidant and anti-atherosclerotic properties through lipid modulation and release of prostaglandin D2,3,4 which may have indirect potential positive effects on erectile function.5,6 It appears that niacin is likely more effective in patients with dyslipidemia and cardiovascular disease.6 However, the exact efficacy of niacin in men with ED as compared with contemporary phosphodiesterase type 5 inhibitor (PDE5i) drugs and the potential effect in combined usage with PDE5i are largely unknown. It is likely that niacin alone is less likely to be effective in patients with severe or medically refractory ED.6 Furthermore, the exact causal effect of niacin on erectile function restoration and the safe threshold of niacin intake for maximum therapeutic remain unknown.

In the evaluation of “antioxidant” supplement’s safety, one must acknowledge that the process of oxidative stress and endothelial remodeling can have wide-ranging effects ranging from physiological to pathological outcomes. While contemporary niacin preparations are likely safe with a good tolerability profile, better chemical engineering is required to capitalize on these advertised benefits more selectively. For many decades, the public has experimented with a variety of vitamin and mineral supplements for a multitude of reasons such as health protection, disease prevention, and longevity; while most supplements are generally labeled “safe”, many patients either are unaware of or fail to take into consideration the basic premise of toxicology whereby excessive dose makes the poison.7 As the health industry continues to promote these supplements for health benefits, there is a need to extrapolate the science through more rigorous clinical trials to provide evidence-based outcomes and better regulate this industry to protect consumer’s safety and ensure corporate governance.

COMPETING INTERESTS

The author declares no competing interests.