Nicotinamide Mononucleotide or NMN is an organic molecule known as a kind of “Fountain of Youth” supplement that shows potential when it comes to positively affecting lifespan. The reason is based on how it acts as a precursor to nicotinamide adenine dinucleotide or NAD.
NAD is responsible for boosting cellular energy production (ATP), promotes efficient metabolism, improves sleep and recovery, and hundreds of other enzymatic reactions crucial to everyday life. We also lose NAD as we age, and scientists hypothesise that increasing NAD levels could help delay ageing. 
Since we can’t exactly eat NAD, primarily because the human body wasn’t designed to absorb NAD through digestion, the next best thing is to get NMN from food sources. Some of these sources are edamame, broccoli, cucumbers, cabbage, avocado, and tomatoes.
While getting NMN from our diet is possible, it’s not as efficient since NMN can only be found in trace amounts. This is where supplementation comes in.
So, what does supplementing NMN do for you?
The biggest reason why NMN supplements are flying off shelves is how it was studied as an anti-ageing supplement. As mentioned, it works by boosting NAD levels, a compound that naturally declines with age. Therefore, boosting NAD levels can indirectly lead to a longer lifespan. 
It also seems to work on other factors that affect ageing such as telomere length – a tail of our DNA that shortens as we age – and sirtuin activity – a family of molecules that exhibit antioxidant properties, fight cellular ageing, lower DNA damage, and is involved in complex anti-ageing processes.
Some scientists believe taking NMN supplements can help with slowing ageing as well as improving our overall health, especially when it comes to lowering cholesterol and triglyceride levels. It’s also been highlighted to promote physical activity. Other studies note that it can possibly provide better eyesight for those who have trouble reading without glasses.
“These findings demonstrate that NAD+ biosynthesis is essential for vision, provide a foundation for future work to further clarify the mechanisms involved, and identify a unifying therapeutic target for diverse blinding diseases.” 
Some studies show NMN supplements help restore damaged heart tissue as well as reverse blood vessel damage caused by ageing. These resulted in better blood flow as well as a stronger heart overall.
“In the present study, 8 weeks of NMN supplementation restored a marker of arterial SIRT1 activity and ameliorated age‐associated endothelial dysfunction and large elastic artery stiffening in male C57Bl/6 mice.” 
While NMN supplementation seems promising, it has to be noted that all the studies used and all the positive results were derived from mostly using mice as subjects. Many studies regarding supplements used animal subjects and drew positive results in humans.
NMN is an important molecule known to promote chemical reactions and processes inside the body that help fight ageing. You can always supply the body with NMN from dietary sources, but the most efficient way is to take NMN supplements. Studies show NMN supplementation has great benefits with regards to slowing ageing as well as overall quality of life and heart health. While the majority of studies do revolve around mice subjects, test results are promising and shouldn’t discourage consumers.