The NAD+ molecule cannot enter the cell membrane due to its enormous size. The membrane doesn’t allow particles to enter inside without using transporters. However, the NMN molecule is smaller than NAD+, and it is absorbed into the cell through the transporters embedded in the surface.

It was previously believed that NMN transforms its absorption. But recent studies show it uses an NMN-specific transporter to make its way into the cell.

Feeding NMN supplements to mice in a study revealed an increase of NAD+ in their livers after a total of only 15 minutes.  Besides using NMN supplements orally, injections also show an increase in NAD+ in various body regions, including the heart, pancreas, skeletal muscle, kidneys, fat tissues, blood vessels, etc.

NMN molecules are generally considered safe and nontoxic, despite high concentrations. Studies showed that a one-year oral administration of the drug did not cause any toxic effects in mice.  The results of these animal studies are encouraging enough that clinical trials on humans have already begun for NMN supplements. Having completed its first-ever clinical trial in humans, the results for NMN display evidence supporting the claim that its single doses are very much harmless.

The only exception is a study published in Japan in 2019. Men used as subjects had increased blood levels of bilirubin following NMN administration. However, these levels did not exceed normal limits. Further studies are currently being conducted to test the effectiveness and safety of its use over the long term. As of now, NMN has no known side effects.

To demonstrate its effectiveness against age-related ailments, NMN was given to mice at doses of up to 300 mg/kg. According to this, a man weighing 165 pounds would need to take 22,500 mg or 22.5 grams of the substance to work. At this dose, NMN would cost over $100 for each dose and more than $35,000 a year, based on its current price!

Nonetheless, humans do not need to consume such high doses for it to be effective. “Volume of distribution” states that rodents like mice, as compared to human beings, require higher doses by a factor of 12.3. As a result, a 300 mg/kg dose in mice would equal 24.39 mg/kg in humans, with a 165-pound person needing only around 1.829 grams to achieve the same effect.

It’s important to remember that a 300 mg/kg dose in mice is relatively large and provides more NMN than is needed for treatment. Which brings us to ask how much NMN do you need to have a noticeable effect?

A study done on rodents concluded that 100 mg/kg of NMN per day resolves most physiological issues related to aging. To find out the dosage for humans, divide this amount by 12.3. Hence, calculating the optimum amount of the substance for a 137-pound adult would be 500 mg of NMN a day

A Japanese team of scientists conducted a study that showed 500 mg of NMN is entirely safe to ingest. With the help of human clinical trials, the team tested oral administrations of NMN supplements up to a dose of 500 mg. The results showed no changes in blood pressure or any other physiological effects.

Another study performed by St. Louis’s Washington University School of Medicine noticed the effects of an oral 250 mg dose of NMN on women for 10 weeks. Findings from this study indicated that doses of 250 mg per day could safely improve insulin sensitivity in muscle, especially in women.

This study by the University of Tokyo proved that men over 65 years of age could benefit from oral doses of 250 mg of NMN per day for 12 weeks. Supplementing the aged men with NMN improved their ability to have better grip, walk faster, and rise from chairs.

So far, NMN has shown potential in improving cardiovascular function, glucose metabolism, and metabolic processes. In addition, testing is being carried out on middle-aged and older adults who suffer from various old age-related diseases like hypertension, obesity, diabetes, and malnutrition. Also, NMN’s safety is currently being studied in clinical trials with long-term administration of 200 to 300 mg/day for up to 24 weeks.

David Sinclair, a professor at Harvard, has studied aging and discusses taking NMN supplements to maintain good health and reduce aging. He advises taking 1 gram of NMN every day, together with metformin, aspirin, and resveratrol.

Based on the studies conducted using humans and animals as subjects, it is concluded that the optimum NMN dose is about 500 milligrams per day. This is the recommended dose for both men and women from ages 30 to 60 years old. To maximize NMN’s benefits, people over 65 can be administered with 750 mg – 1000 mg of NMN supplement a day.