Oh boy … there’s a lot of literature haha … let me link you a few key studies for now and I can go over them later today…

“niacin improves AD cognitive ability through: reducing Aβ formation, improving mitochondrial metabolism, regulating autophagy, & reducing inflammation”

Nicotinic acid supplementation contributes to the amelioration of Alzheimer’s disease
https://atm.amegroups.com/article/view/101529/html

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“Dementia is CAUSED by severe niacin insufficiency”

Conclusion:
“niacin protects against AD and age related cognitive decline”

Dietary niacin and the risk of incident Alzheimer’s disease and of cognitive decline
https://jnnp.bmj.com/content/75/8/1093

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“After the Alzheimer’s disease animal models received niacin, they ended up with fewer plaques and they have improved cognition,” Landreth said, “and we directly showed that these actions were due to the HCAR2 receptor.”

Past epidemiology studies of niacin and Alzheimer’s disease showed that people who had higher levels of niacin in their diet had diminished risk of the disease, Landreth said. Niacin is also currently being used in clinical trials in Parkinson’s disease and glioblastoma.

To further their research into niacin and the brain, Landreth and Moutinho are collaborating with Jared Brosch, MD, associate professor of clinical neurology, who is applying for a clinical pilot trial to study the affects of niacin and the human brain.
https://medicine.iu.edu/news/2022/03/niacin-alzheimers-research

^
Please don’t use the sustained-release Niaspan Merck/Pfizer make, note:

The niacin receptor HCAR2 modulates microglial response and limits disease progression in a mouse model of Alzheimer’s disease
https://www.science.org/doi/10.1126/scitranslmed.abl7634

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This is just a sample for dementia. In terms of more broadly, neurodegeneration, here is a beautiful (also) recently-conducted and published double-blinded randomized placebo-controlled clinical trial proving how even low-dose flush niacin (immediate release nicotinic acid) evidently is seeming to be curing full-blown Parkinson’s disease in (already likely incoming, very disabled) Veterans at the VA. In fact, for ethical reasons of course, they had to stop the randomization across intervention vs. control after 6 months to inform all participants that niacin was pretty much curing the participants who were randomized to it and then open-label administer the flush niacin to everyone thereafter. Imagine how excited the participants who were randomized to the control placebo were! …

Low-Dose Niacin Supplementation Improves Motor Function in US Veterans with Parkinson’s Disease: A Single-Center, Randomized, Placebo-Controlled Trial
https://www.mdpi.com/2227-9059/9/12/1881

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With just a sample of the literature from above for now and per my personal observations of older adults ranging from cognitive function starting to decline all the way to full-blown dementia on their deathbed, all stages are able to be reversed and of course more readily with less actual neurodegeneration having had developed/proceeded. This means, in the case of your husband, he will likely become just as even more sharp (and maybe handsome as time goes forward and he reverse-ages) like the man you met before you married him with continued dosing. What is imminent, per the clinical + research literature and all my observations, is that he will be objectively and subjectively feeling better likely within a few weeks (if) than he has been & felt in perhaps decades with sufficient dosing of flush niacin (immediate release nicotinic acid) + glutamine (again, per https://www.hom3ostasis.com/protocol – please try to get the PureBulk only). The glutamine added in now will even further harness niacin’s power to turn into bigger molecules (NAD+ / NAADP), i.e., protons (H+) / proton motive force = potential energy (just as is it is released from stored bonds in our body (but with niacin, not just in adipose tissues but ubiquitously through all cells) when we kinetically place our body into motion through physical activity/exercise: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7093185/ but without investing any actual “work” / labor as in exercising to do it and EXPONENTIALLY more efficiently) to clear aggregated inflammation, debris, and ultimately the disposition of the brain (and whole body up to that point) as a result of not having perhaps even 1/100th enough flush niacin in diet each day over X # of decades (with the latter decades really catching up as the body breaks down). Meanwhile, the NAD+ (and NADP, NADPH, and NADH) made as a result of supplying enough niacin + glutamine exogenously per this protocol will in turn thereafter also fuel the extra glutamate (converted from the reaction of glutamine catalzying niacin to NAD+ / NAADP) to provide more goodies through the citric acid cycle and ultimately ATP to continue to fuel this entire therapy from that first step each time to feel better, heal faster compoundingly forward.

Please let me know if this makes sense. And yes, these “doctors” are a disgrace.