NAD+ and a busy cell

Energy use and DNA repair

NAD+ is nicotinamide adenine dinucleotide, a coenzyme involved in releasing energy from food. It carries electrons between reactions. It is also consumed by enzymes involved in DNA repair, gene regulation and inflammation. The review of NAD+ metabolism during ageing describes how those competing uses can affect the available supply.

This feels busier than the usual picture of a depleted battery. My objection to that picture is the missing demand side. NAD+ has several jobs, and restoring a blood measurement leaves questions about what is happening inside a particular tissue. NAD+ has a different chemical structure from a peptide, despite appearing beside peptides in so many health claims.

Muscle insulin sensitivity

I’d linger over the NMN muscle experiment: a 10-week NMN study in postmenopausal women with prediabetes. NMN supplies material for cells to make NAD+. Muscle insulin sensitivity improved: under controlled insulin and glucose conditions, muscle handled glucose more effectively in response to insulin.

Body composition and HbA1c, the longer-term blood-sugar reading, remained unchanged. The mix of improved and unchanged measurements is useful. It narrows the finding to a particular response in a particular group, rather than giving every metabolic claim a favourable answer.

I’m inclined to take that muscle response seriously. Extending it to weight loss, disease prevention or renewed energy in everyone would outrun the trial.

Blood NAD+ measurements

A 60-day NMN trial in healthy middle-aged adults reported higher blood NAD+, improved walking distance and better quality-of-life scores compared with placebo. Blood NAD+ rose at days 30 and 60, with no reported safety issues at the amounts tested. A separate 8-week NR trial in healthy overweight adults also raised blood NAD+, with no significant difference in adverse events from placebo.

NR and NMN are precursors used to make NAD+; the trials administered those substances rather than NAD+ itself. Across the field, a 2025 review found limited human efficacy and sparse tissue-specific data despite consistent blood increases. I give that wider assessment more weight than an isolated attractive endpoint. The field still needs clearer links between added supply and sustained health changes.

Does NAD cause weight gain?

The NMN study in women with prediabetes found no change in body composition. That result provides no evidence of weight gain from the intervention in that trial, and no general weight-loss result either. The exact substance, population and outcome matter when the question expands to all products described as NAD+.

Infusions and long-term safety

The short oral trials offer reassuring observations within their own durations and populations. Long-term safety remains less clear. Intravenous NAD+ has much less controlled evidence, and compounded injectable material raises separate questions about contamination and actual contents. Oral precursor findings cannot resolve those questions.

There is also a theoretical concern that extra NAD+ could support an existing cancer’s metabolism. The trials discussed here did not demonstrate that harm. I’d treat cancer metabolism as a question about biological context; the concern leaves the risk of an individual increase unsettled. NAD+ and its precursors have no approved drug indication for reversing ageing; compounded injectable NAD+ is not FDA-approved. The human-evidence review leaves plenty of work before a broad rejuvenation claim becomes convincing.