What are the effects if you take NAD every day?
Taking 600-900 mg of a NAD supplement per day raises your NAD levels and provides some benefit for endurance, but long-term safety has not yet been properly studied.
NAD supplements (such as NMN) raise your NAD levels in the blood -- that has been fairly well established. In a randomised, double-blind study of 80 healthy, middle-aged adults, NAD levels rose significantly at all doses from 300 to 900 mg per day after 60 days. Levels were highest at 600 and 900 mg1,2.
In terms of physical effects, participants in all NMN groups performed significantly better on a six-minute walk test than the placebo group, already after 30 days. Those taking 600 or 900 mg also reported a measurably improved sense of health. On blood sugar regulation, the supplement had no demonstrable effect in this study.
A small study of 11 Japanese men taking 250 mg per day confirmed the rise in NAD. In three participants who had excessively high insulin release after meals, that response appeared to decrease slightly, but a group of 11 is too small to draw much from3. For people with chronic fatigue syndrome (ME/CFS), there is moderate support: a combination of CoQ10 (200 mg) and NADH (20 mg) over 12 weeks significantly reduced cognitive fatigue and improved quality of life. This applies specifically to ME/CFS patients only4.
On safety, there are two points. Up to 900 mg per day, NMN was well tolerated in the 60-day study: no side effects or abnormal laboratory values. Laboratory research does reveal a theoretical risk: if the supplement accumulates in tissues and is not converted quickly enough, an enzyme can be activated that breaks down nerve fibres. Whether this occurs in humans during normal use is unknown5. In addition, smokers taking a different NAD precursor showed a dose-dependent increase in a marker for possible DNA instability, without any reduction in smoking-related DNA damage6.
People respond very differently to the same dose: the increase in NAD varied by a factor of three to more than ten within the same dosage group. A single standard dose therefore does not work equally well for everyone. And because all studies lasted a maximum of 60 to 90 days in relatively small groups, we simply do not yet know what daily long-term use does.
All claims are based on two publications from the same study (PMID 36482258 and PMID 38430946, 80 participants), one small open-label study (PMID 38191197, 11 participants), one study in ME/CFS patients (PMID 34444817), one laboratory study on the nerve fibre risk (PMID 36657725), and one older study in smokers using a different NAD precursor (PMID 10030610). The large study is the strongest source, but has a short duration of 60 days and a limited number of participants.