NAD+, NMN and NR: Promising Biology, Thin Human Evidence

NAD+ is a coenzyme every cell uses to run energy metabolism, and it is also consumed by the enzymes that repair DNA and by the sirtuins involved in regulating ageing. It falls substantially with age. All of that is well established.

The supplement industry built on that fact has run considerably ahead of the human data.

What the trials actually show

• NR and NMN reliably raise blood NAD+ levels in humans. This is the strongest and most consistently replicated finding
• What raising it accomplishes is far less clear. Trials measuring insulin sensitivity, muscle function, cardiovascular markers and physical performance have produced mixed and mostly modest results
• The dramatic mouse results — restored muscle function, improved metabolic health — have not translated cleanly. Mice are short-lived and their NAD+ metabolism differs
• No human trial has run long enough to say anything about lifespan or healthspan, and none realistically can in the near term

Raising a biomarker is not the same as producing a benefit. The gap between those two statements is where most of this category's marketing lives.

The things that lower NAD+ in the first place

The enzyme CD38 rises with age and inflammation and consumes NAD+. PARP enzymes consume it repairing DNA damage. Both are downstream of the same inputs: chronic inflammation, metabolic dysfunction, alcohol, and constant oxidative load.

• Exercise raises NAD+ through the salvage pathway, at no cost
• Fasting and caloric restriction do the same and activate the sirtuins directly
• Reducing alcohol matters, because ethanol metabolism consumes NAD+ heavily
• Plain niacin and nicotinamide from food feed the same pathway for a fraction of the price

If you are going to try it

NR has the longer safety record and more published human work; NMN has more enthusiasm and a murkier regulatory position in some countries. Typical doses are 250–500 mg daily. Both appear safe at those levels over the periods studied.

The honest position is that this is a reasonable bet on interesting biology, not an established intervention. If the budget is finite, the fasting and the training come first — they act on the same pathway, and their evidence is not in question.