Highlights

  • NMN improves walking speed, according to an analysis of 8 trials. 
  • NMN improves insulin sensitivity, but only at low doses, according to an analysis of 4 trials. 
  • NMN reduces a marker for liver injury, ALT, according to an analysis of 6 trials. 

NMN is a precursor to NAD+ (nicotinamide adenine dinucleotide) and, when consumed, is capable of elevating NAD+ levels. By boosting NAD+, NMN has been shown to counteract key aspects of aging in a slew of animal studies. This potentially makes NMN the perfect supplement for NAD+ deficiency, which is prevalent in middle-aged and elderly individuals. However, there exist few studies testing NMN’s effects on these populations. 

To better understand the effects of NMN on human aging, scientists in China gathered the studies pertinent to NMN’s effects on muscle and liver function. They focused on randomized clinical trials (RCTs), which are the gold standard of scientific research in humans. As published in their recent meta-analysis, the researchers conclude that “NMN is an encouraging and considerable drug for anti-aging treatment.”

NMN Counteracts Muscle and Liver Aging

The China-based researchers found a total of 13 RCTs from 9 studies published between 2021 and 2023. All the studies were conducted in either Japan or China, except for one study conducted in the United States. The duration of the RCTs ranged from 4 to 24 weeks, and the dose of NMN administered ranged from 250 to 1250 mg/day. Notably, these studies were not large, totaling only 412 participants. 

Muscle Function 

Gait speed was assessed in 8 trials, with the analysis showing that NMN increases gait speed by about 1 ft/s. However, this improvement was highly variable between participants. Moreover, the increase in gait speed was doubled in participants under the age of 60. In contrast, grip strength, which was assessed in 7 trials, did not improve, except for participants over the age of 60. 

(Wang et al., 2025) NMN Improves Gait Speed. Based on 8 trials, the overall gait speed (dotted red line) was significantly greater than zero.

In 5 trials, the sit-to-stand test was conducted. This test calls for the participants to sit down and stand up from a chair 5 times. The analysis showed that NMN did not significantly improve the time it took to complete the sit-to-stand test. Overall, these proxy measures of muscle function suggest that NMN improves gait speed, especially in people below the age of 60. Additionally, NMN appears to improve grip strength in people over the age of 60. 

Insulin Resistance 

Insulin resistance occurs when our cells become resistant to the effects of insulin, which is a hormone that signals our cells to take in glucose for energy. As can be surmised, insulin resistance is not good for health and longevity, as it can lead to chronic diseases such as diabetes, heart disease, and Alzheimer’s dementia. Based on a 4-trial analysis, NMN does not improve insulin resistance. However, a sub-analysis showed that 300 mg or less of NMN does counteract insulin resistance. 

Liver Function

To assess liver function, the researchers analyzed the common clinical markers AST (aspartate aminotransferase) and ALT (alanine aminotransferase), which were measured in 6 trials. While NMN did not significantly change AST levels, the analysis showed that NMN significantly lowered ALT levels. Moreover, the improvements in ALT were more pronounced when NMN was taken for less than 10 weeks or in participants under the age of 60. 

(Wang et al., 2025) NMN ALT Levels. Based on 6 trials, the overall concentration of ALT (dotted red line) was significantly lower than zero.

A More Complete Story 

“In conclusion, NMN, a drug with proven safety and without serious adverse drug reactions, could serve as a safe alternative treatment for alleviating aging in middle-aged and elderly individuals. Considering the scarcity of available data and the suboptimal quality of completed trials, it is necessary to conduct further well-designed, multi-center randomized controlled trials (RCTs) to specifically investigate the influence of NMN treatment,” said the authors of the study.

As it pertains to further RCTs, more of them have been published since 2023. For example, a Japanese study showed that NMN counteracts age-related gait speed decline. That is, while NMN did not improve gait speed, it prevented the decline in gait speed observed in the placebo group. However, it should be pointed out that the participants in this study did not exercise regularly. What’s more, other RCTs have shown no effect on gait speed in exercised participants, suggesting that NMN may only improve gait speed in older adults who do not exercise. 

In a Harvard conducted RCT, NMN had no effect on liver enzymes (AST and ALT) in middle-aged and elderly adults who were overweight or obese. NMN (2 grams) also had no effect on insulin resistance, supporting the idea that only low doses of NMN counteract insulin resistance. Additionally, NMN did not improve muscle strength, muscle fatigability, or stair-climbing ability, suggesting it did not improve muscle function. 

Still, these recent RCTs do not change the final conclusion of the authors:

“Although the current meta-analysis showed a statistical benefit, we would like to pay attention to potential drawbacks associated with the quality, heterogeneity, and small sample size of the studies included. Therefore, further long-range clinical trials are required to evaluate the influence of NMN on muscle and liver functions in middle-aged and elderly populations.”