Nicotinamide riboside is a nucleoside, which incorporates nicotinamide and ribose into a single chemical . Nicotinamide riboside is newly identified nicotinamide adenine dinucleotide (NAD+) precursor and data also suggests that it is the only vitamin precursor that supports neuronal NAD+ synthesis .
Sources of Nicotinamide Riboside
NR (sometimes referred to as the “hidden vitamin”) is found naturally in trace amounts in milk and other foods. Cow milk typically contains ~12 µmol NAD+ precursor vitamins/L, of which 60% is present as nicotinamide and 40% is present as NR .
Effects on Muscle Tissue
According to a 2016 study published in the journal Science , nicotinamide riboside has the capacity to stimulate the regeneration of lost muscle tissue in elderly mice, while also increasing their lifespan.
The development of stem cells (SCs) into specialized cells relies on energy produced by mitochondria. This study also showed that mitochondrial oxidative respiration is important for the functional maintenance of multiple types of adult SCs during aging. When stem cells develop, they use up cellular supplies of a compound called nicotinamide adenine dinucleotide (NAD+), which happens to play a vital role in ensuring the healthy functioning of mitochondria . The loss of cellular NAD+ leads to loss of mitochondrial homeostasis which hampers self-renewal capacity of muscle SCs .
Increasing Life Span
Strategies that conserve cellular NAD+ may reprogram dysfunctional SCs and improve lifespan in mammals . Scientists explain that by administration of NAD+ precursors (such as NR) they were able to restore communication inside cells between the nucleus and mitochondria in older mice [6,7,8]. As this communication is broken down, aging accelerates. Subsequent tissue samples revealed that key biological hallmarks were comparable to those of much younger animals .
Why mitochondrial homeostasis is disrupted with age and whether this process can be slowed or even reversed is still a matter of debate.
Effects of NR in Humans
So far, the only human trial was performed by ChromaDex  which acquired intellectual property on uses and synthesis of NR. Data presented in the study indicates that single doses of Niagen® NR can elevate the co-enzyme NAD+ in the blood by as much as 2.7-fold .
The second human clinical trial is under way and will be a randomized, double-blind, placebo controlled parallel study in 140 healthy adults ranging in age from 40-60, which will examine the benefits of Niagen® if taken daily for eight consecutive weeks .
Scientists are still exploring whether the compound can be used to safely treat rare mitochondrial diseases or more common diseases such as Type 1 and Type 2 diabetes .
Hongbo et al.  observed no side effects from NR administration even at very large doses. Same was reported by first human clinical trial .
It should be noted that majority of these studies are at least partially conducted by patent holders. More large-scale, independent and unbiased studies are warranted before you get to excited. Article to be updated regularly as new evidences emerge.
Bogan, Katrina L., and Charles Brenner. “Nicotinic acid, nicotinamide, and nicotinamide riboside: a molecular evaluation of NAD+ precursor vitamins in human nutrition.” Annu. Rev. Nutr. 28 (2008): 115-130.
Trammell, Samuel AJ, et al. “Nicotinamide Riboside Is a Major NAD+ Precursor Vitamin in Cow Milk.” The Journal of Nutrition 146.5 (2016): 957-963.
Zhang, Hongbo, et al. “NAD+ repletion improves mitochondrial and stem cell function and enhances life span in mice.” Science (2016): aaf2693.
- Cameron, David (19 December 2013). “A New—and Reversible—Cause of Aging”. Harvard Medical School. Retrieved 10.5.2016.
- Bellman, Gary. “New Elixir of Youth? Researchers Develop a Drug That Can Reverse Aging in Animal Models”. Male Anti-Aging Institute. Retrieved 10.5.2016.
Gomes, Ana P., et al. “Declining NAD+ induces a pseudohypoxic state disrupting nuclear-mitochondrial communication during aging.” Cell 155.7 (2013): 1624-1638.
Inc., ChromaDex,. “Results from First Human Clinical Study Demonstrate ChromaDex’s Niagen(R) Nicotinamide Riboside Effectively Increases the Co-enzyme NAD+ and is Safe”. GlobeNewswire News Room. Retrieved 10.5.2016.
Inc., ChromaDex,. “ChromaDex Initiates Second Human Clinical Study on NIAGEN® -The World’s First and Only Commercially Available Form of Nicotinamide Riboside (NR)”. GlobeNewswire News Room. Retrieved 10.5.2016.