At what age does taking NAD+ supplements make sense?

Human studies on NAD+ supplementation have been conducted almost exclusively in middle-aged and older adults, and in people with cardiometabolic risk factors such as overweight or elevated blood sugar. No study exists that establishes a concrete threshold age at which supplementation would become worthwhile. The reason researchers focus on older adults is the assumption that NAD+ levels decline with age, but that decline has been less well demonstrated in humans themselves than in animal and laboratory studies.

The only thing human studies have consistently shown so far is that NAD+ levels in blood and tissues do genuinely rise when you take nicotinamide riboside (NR) or nicotinamide mononucleotide (NMN). That is the most robust finding. Both compounds are well tolerated; serious side effects have not been reported in the studies conducted.

The crucial question is whether higher NAD+ levels also lead to something you notice or can measure: better muscle strength, sharper memory, or a healthier heart. Clear evidence for this in humans does not yet exist. The available studies are small, use varying doses, and were too short in duration to draw firm conclusions. The results are mixed and insufficient to say that supplementation improves those functional outcomes.

In mouse studies the results are more promising. In mice with Alzheimer's pathology, NR reduced inflammatory responses, DNA damage, and senescent cells, and also improved cognitive function. In other animal models, NAD+ replenishment improved heart failure and arterial calcification. But these are animal models, and the translation to humans has not yet been demonstrated.

Practically speaking: if you are over 40 and want to experiment, the available studies do not exclude you, but they offer no guarantee of a measurable result either. There is no reason to assume that younger, healthy adults benefit, simply because they have barely been studied and their NAD+ levels have presumably not yet declined significantly. The safety of NR and NMN is reasonably well documented for short-term use; virtually nothing is known about long-term use in younger people.