What are the key points in brief?
- If brain fog occurs together with persistent fatigue, the common causes of fatigue can be a starting point1.
- These include sleep disorders, breathing disorders during sleep, depression and severe psychosocial strain1.
- For NAD+ precursors, functional effects in humans were inconsistent and often showed no difference, according to a review2.
What does “brain fog” mean on this page?
On this page, “brain fog” stands for concentration problems, everyday forgetfulness and a feeling of not being mentally clear. It describes symptoms. The term names no cause.
Which causes can be discussed with a doctor?
If you experience brain fog together with persistent fatigue, you can use the work-up of fatigue as a starting point. According to a review in Deutsches Ärzteblatt, the most common causes of persistent fatigue are sleep disorders, breathing disorders during sleep, depression and severe psychosocial strain1.
A conversation, a physical examination and simple lab tests come first. Further tests follow if there are additional symptoms or findings1. More on this is on the page What can lie behind fatigue before considering NAD+ infusions?.
What is shown about NAD+ and mental performance?
A systematic review from 2026 found inconsistent and often absent effects of oral NAD+ precursors on function and other health markers in humans. Clinical efficacy for anti-aging and wellness is regarded there as not established2. A critical review on NR sees few clinically relevant effects3.
How do you describe brain fog in a doctor's appointment?
Concrete observations can help the practice. You can answer these questions for yourself beforehand:
- Since when have you noticed it, and has it changed?
- At what time of day is it most noticeable?
- What is difficult: reading, following conversations, planning, remembering things?
- How do you sleep, and do you feel rested in the morning?
- Which medicines, dietary supplements or other substances do you take?
The five-step preparation turns your answers into notes for the doctor's appointment.
Which sources does this page rely on?
- Maisel P, Baum E, Donner-Banzhoff N (2021). Fatigue as the Chief Complaint. Deutsches Ärzteblatt International. DOI: 10.3238/arztebl.m2021.0192
The paper summarises how family doctors may assess persistent fatigue. It is a review based on a literature search. Its authors suggest that history, physical examination and simple laboratory tests may usually be enough, with further tests mainly when other findings point that way.
- Gallagher C, Emmanuel OO (2026). NAD⁺ supplementation for anti-aging and wellness: A PRISMA-guided systematic review of preclinical and clinical evidence. Ageing Research Reviews. DOI: 10.1016/j.arr.2026.103057
The review asks what studies on NAD+ products show for ageing and well-being. It systematically assesses 113 studies, 33 of them in humans. NR and NMN may raise NAD levels and appear well tolerated, while a clinical benefit remains open, and suitable trials of NAD+ infusions were lacking.
- Damgaard MV, Treebak JT (2023). What is really known about the effects of nicotinamide riboside supplementation in humans. Science Advances. DOI: 10.1126/sciadv.adi4862
The review checks what is actually established about nicotinamide riboside in humans. It critically assesses 25 published human studies. Clinically relevant effects were rare, and reported effects may often be overstated in the literature.