Observations and human trials
Insulin response and distance walked
Here the account gets a human scale. Muscle measurements and a walking outcome deserve room for their differences.
Muscle biopsies in sarcopenia
A study of muscle biopsies from 119 older men across three populations associated sarcopenia, the loss of muscle with ageing, with impaired mitochondrial energy metabolism, fewer mitochondria and low NAD+ through disrupted synthesis and salvage. This was an observational biopsy study.
The finding gives a depleted supply a recognisable human setting. It also leaves a question open: how much of the pattern would change if the supply changed? I’m willing to regard the observation as a strong reason for further investigation. The answer requires an intervention with outcomes of its own.
Muscle response after NMN
In prediabetic, postmenopausal women given oral NMN for 10 weeks, muscle insulin sensitivity improved and insulin signalling changed. Body composition and HbA1c, a measure of longer-term glucose exposure, were unchanged. The result concerns NMN, a precursor used to make NAD+.
Muscle insulin sensitivity describes how effectively the muscle responds to insulin. The specificity is satisfying: a metabolic response improved, while broader measures stayed put. Turning the whole trial into a claim about feeling energetic would spend evidence the experiment did not earn.
The women’s prediabetic and postmenopausal status matters to the account. It would be careless to let those particulars disappear when describing the result to a different population.
Walking distance in middle-aged adults
Another randomized, double-blind, multicentre NMN trial ran for 60 days in healthy middle-aged adults. Blood NAD+ increased, and walking distance and quality-of-life scores improved compared with placebo. Walking puts a physical task beside the talk of vitality.
Still, the duration remains 60 days, and the participants remain healthy middle-aged adults. Those features deserve as much space as the favourable result. The later review of human evidence describes inconsistent translation from rising blood NAD+ to clinical outcomes. I’d like a longer account of function across different starting states, especially alongside tissue measurements.
