NAD+ for Brain Fog and Cognition: The Evidence After 45

In aged mice and in mouse models of Alzheimer's disease, raising NAD+ — usually with the precursors NR or NMN, occasionally with NAD+ directly — improves performance on memory and learning tasks, reduces markers of brain inflammation, improves blood flow in the brain, and in some models slows the accumulation of the proteins associated with dementia. These are consistent findings from multiple laboratories, and they are the origin of nearly every claim made for NAD+ and the brain.

The caveats are the usual ones and they are large. Mice are not people; mouse cognition is a maze; the amounts used, scaled to a human, are often far beyond anything given clinically; and the history of neuroscience is a history of treatments that cured Alzheimer's in mice.

Small. That is the first word. The human trials of NAD+ precursors that measured cognition have enrolled dozens of people, not thousands, and have run for weeks to a few months.

Their findings, taken together: NAD+ precursors reliably raise blood NAD+ levels in older adults, and are well tolerated. On cognition, most trials in healthy older adults found no significant difference from placebo on standard tests. A few found improvements on specific measures — processing speed in one, a memory subscore in another — that did not replicate across studies and that are consistent with chance when many measures are tested. Small trials in people with mild cognitive impairment or early Parkinson's disease have shown changes in brain metabolism on imaging, which is interesting, and modest or no change in symptoms, which is the part that matters.

There are no published trials of NAD+ injection for cognition in healthy adults. Every human study used oral precursors or IV NAD+ in a research setting, and the main page is candid that the subcutaneous route itself is untested.

The honest summary: the hypothesis is sound, the animal data are strong, the human data are small and mostly negative for cognition in healthy people, and the subcutaneous injection has not been tested for it at all.

The reason this matters is that "brain fog" after forty-five is very often a symptom of something with a better-evidenced treatment than NAD+. Poor sleep and undiagnosed sleep apnea are the commonest. Then the hormonal transitions — perimenopause in women, low testosterone in men — which the perimenopause brain fog and low testosterone pages cover. Then thyroid, iron and B12 deficiency, depression, medication side effects (antihistamines, sleep aids, some blood-pressure drugs), regular alcohol, and uncontrolled blood sugar.

Every one of those is on the brain fog workup, every one is checked with a history and a panel, and every one has a treatment with more evidence behind it than NAD+. A person who starts NAD+ for brain fog without that workup is, in effect, treating the mouse's problem and not their own.

After the workup. For the person whose sleep is addressed, whose hormones and thyroid and iron are in range, who is not depressed or drinking more than they should, and who still feels that their thinking has lost an edge, NAD+ is a reasonable thing to try with expectations set by the evidence above: well tolerated, plausible, unproven for this purpose, and to be judged by how they feel over a defined period rather than continued on faith. We say that at the consultation, and we say it again at review.