Creator: Help Dementia Editorial Team
Published: 2026-04-23T06:49:04

Reviewed by the Help Dementia Editorial Team — our editors review every article for accuracy against guidance from the National Institute on Aging, the Alzheimer’s Association, and peer-reviewed sources.

New research sits at the center of this dementia and brain health question.

Recent research has identified several supplements that show promise in protecting the brain against Alzheimer’s disease biomarkers—the cellular and protein signatures that indicate emerging neurodegeneration. A study published in April 2026 found that higher vitamin D levels in midlife are associated with lower tau protein accumulation in the brain years later. Meanwhile, separate research on NAD+ supplementation has demonstrated the ability to reverse disease markers like amyloid and tau buildup in mice, even restoring cognitive function in advanced disease models.

These findings are generating cautious optimism among researchers and caregivers searching for preventive approaches, though experts emphasize that most evidence remains in early laboratory stages rather than human trials. The appeal of supplement-based protection against Alzheimer’s is understandable. Unlike expensive disease-modifying drugs that work for only a fraction of patients, supplements are accessible, affordable, and often tolerable for long-term use. However, the research landscape remains fragmented, with different supplements showing different effects on different biomarkers, and significant gaps in understanding optimal dosing, safety profiles, and whether improvements in mice translate to meaningful protection in people.

What Do These Biomarkers Tell Us About Alzheimer’s Risk?
The NAD+ and Lithium Research: Reversing Disease in Animals
Arginine and the Anti-Inflammatory Approach
Vitamin D—The Longest-Studied Candidate with Mixed Results
The Critical Gap—No Human Evidence of Cognitive Protection
Interpreting the Research Responsibly
The Future of Supplement-Based Prevention
Conclusion

What Do These Biomarkers Tell Us About Alzheimer’s Risk?

alzheimer‘s disease develops through measurable changes in the brain long before memory loss appears. The two hallmark proteins are amyloid beta, which clumps into plaques, and tau, which forms tangles inside neurons. A newer biomarker, phosphorylated tau 217 (p-tau217), has emerged as a particularly useful indicator because it can be measured in blood tests, unlike brain imaging that requires expensive scans. When the April 2026 vitamin D study found lower tau levels in people with higher midlife vitamin D, it was measuring exactly this kind of early structural change—decades before symptoms might develop. The significance lies in catching pathology early. Someone with low tau and amyloid in their sixties might never develop dementia in their lifetime, while another person with high levels might begin showing cognitive decline in their seventies.

For this reason, any supplement that shifts these markers in the protective direction is worth investigating carefully. The NAD+ mouse studies were particularly striking because they showed not just slowing the disease but actually reversing established tau and amyloid accumulation—a much more ambitious claim than simply preventing buildup. However, a critical limitation emerges when examining these biomarkers across different supplements. The vitamin D research found no connection between vitamin D levels and amyloid beta, only tau. This specificity matters because Alzheimer’s typically involves both proteins, not just one. A supplement that addresses only one piece of the puzzle may offer incomplete protection or no protection at all in real people, despite promising biomarker changes in laboratory conditions.

What Do These Biomarkers Tell Us About Alzheimer's Risk?

The NAD+ and Lithium Research: Reversing Disease in Animals

NAD+ is a coenzyme present in every cell that declines with age and appears depleted in Alzheimer’s pathology. Recent research restored NAD+ levels in mouse models and observed a striking result: disease markers reversed. Treated mice showed normalized blood levels of p-tau217, the same clinical biomarker used in human Alzheimer’s drug trials. Cognitive function, measured through maze navigation and other behavioral tests, was fully restored even in mice with advanced disease features. These results suggest that age-related NAD+ decline might be a treatable cause of neurodegeneration rather than an inevitable consequence. Lithium has an even longer research history, with several studies showing it protects neurons and reverses damage in mouse models of Alzheimer’s disease.

In one line of research, replenishing brain lithium stores reversed memory loss in mice and protected against tau tangles. The mechanism appears to involve lithium’s ability to inhibit glycogen synthase kinase-3 beta, an enzyme that promotes tau phosphorylation. Unlike NAD+, which is a natural metabolite, lithium is a pharmaceutical-grade mineral that must be dosed carefully to avoid toxicity. The major limitation with both NAD+ and lithium research is the translation gap. Mouse brains, while structurally similar to human brains, process drugs and supplements differently, have shorter lifespans measured in months rather than decades, and don’t replicate the complex comorbidities that exist in older humans with early Alzheimer’s. A supplement that reverses pathology in a 12-month mouse study may have modest or negligible effects in humans taking it for years. Additionally, neither NAD+ nor lithium supplementation has been tested in large, randomized human trials specifically designed to measure cognitive outcomes over years of treatment.

Arginine and the Anti-Inflammatory Approach

Arginine is an amino acid that plays multiple roles in vascular health and neuroinflammation. Research published in November 2025 showed that oral arginine supplementation lowered plaque levels and reduced inflammatory markers in animal models of Alzheimer’s disease. Behavioral improvements were observed in both fruit flies and mice, suggesting the effect might reflect a fundamental biological mechanism rather than species-specific noise. The anti-inflammatory pathway is attractive because chronic neuroinflammation is increasingly recognized as a driver of neurodegeneration, potentially even more central than amyloid and tau accumulation alone. What distinguishes the arginine research from the others is its focus on inflammation as the primary therapeutic target. While NAD+ and lithium work through direct effects on protein misfolding, arginine appears to work by reducing the immune response—the brain’s prolonged inflammatory state that damages healthy neurons over decades.

This mechanism-level difference could be clinically important. Some Alzheimer’s cases may be primarily driven by excessive inflammation, while others are driven by protein accumulation. An arginine supplement might prevent or slow disease in the inflammation-predominant subset while having little effect on the amyloid-primary cases. The limitation here is specificity of measurement. The animal studies showed reduced plaques and inflammation markers, but didn’t clearly distinguish whether the cognitive improvements came from reduced inflammation, reduced plaques, or both. Arginine also affects vascular function and has been studied for cardiovascular benefits, which makes it difficult to isolate whether brain protection comes from direct neurological effects or indirect benefits from improved blood flow to the brain.

Arginine and the Anti-Inflammatory Approach

Vitamin D—The Longest-Studied Candidate with Mixed Results

Vitamin D is perhaps the most extensively studied supplement for brain health, with decades of epidemiological data linking low vitamin D levels to higher dementia risk. The April 2026 study published in a major journal added new evidence by following people over time and measuring both vitamin D status and actual tau levels in the brain. Those with higher vitamin D in midlife showed significantly lower tau accumulation in later brain imaging, an important finding because tau begins accumulating decades before memory loss appears. However, the same study found no connection between vitamin D levels and amyloid beta, the other key Alzheimer’s protein. This suggests vitamin D might protect against one pathway of Alzheimer’s disease—the tau-based pathway—while being irrelevant to the amyloid-based pathway. In practical terms, someone with naturally high vitamin D might successfully prevent tau tangles but still develop amyloid plaques through a separate mechanism.

The protective effect, if real, appears incomplete. The vitamin D finding also comes with a tradeoff. The study measured observational associations, not causation. People with high vitamin D might differ in countless other ways—diet, exercise, sun exposure, socioeconomic status, cognitive reserve—that independently protect their brains. Only randomized controlled trials giving some people vitamin D supplements and others placebo, then following their brain imaging and cognition over decades, could answer whether vitamin D itself causes protection or merely correlates with other protective factors. Such trials are underway but results remain years away.

The Critical Gap—No Human Evidence of Cognitive Protection

Across all four supplement pathways—vitamin D, NAD+, lithium, and arginine—the research landscape shares a fundamental limitation: we have no evidence that any of them actually prevent dementia in humans. The vitamin D study showed tau reduction. The NAD+ study reversed disease markers in mice. The lithium research showed cognitive recovery in animals. The arginine work demonstrated plaque reduction in models. None of these studies measured whether people taking these supplements actually avoided cognitive decline or dementia diagnosis. This gap matters enormously for decision-making. A biomarker change might be necessary but not sufficient for clinical benefit.

It’s theoretically possible that reducing tau or amyloid by 20 or 30 percent in a mouse’s brain has meaningful functional impact, while reducing it by the same percentage in a human with multiple comorbidities, medication interactions, and decades of accumulated damage provides no measurable cognitive protection. Researchers have observed this pattern repeatedly in Alzheimer’s drug development—compounds that clear plaques effectively in trials still fail to slow cognitive decline meaningfully. Additionally, dosage and safety data remain sparse for most of these supplements in humans. NAD+ precursors have been tested in small trials, but not at doses or durations needed for brain protection. Lithium has known safety concerns including thyroid effects and kidney stress, requiring careful monitoring. Arginine can interact with blood pressure medications and might affect cardiovascular function unpredictably in older adults. Vitamin D supplementation above certain levels has been linked to hypercalcemia and increased fracture risk in some populations. Moving from “promising in rodents” to “safe and effective in older humans” requires careful dose-finding and safety studies that are still ongoing.

The Critical Gap—No Human Evidence of Cognitive Protection

Interpreting the Research Responsibly

The consistent message from researchers studying these supplements is not that they don’t work, but rather that we genuinely don’t know yet whether they work in humans for cognitive protection. A May 2025 comprehensive review examining multiple supplement pathways for Alzheimer’s concluded that inconsistent findings and major gaps in human safety and dosage data highlight the need for rigorous, large-scale trials. This wasn’t dismissal—the researchers acknowledged plausible mechanisms and early-stage promise—but rather honest assessment of what the evidence actually shows.

For someone with a family history of dementia or early biomarker changes, the situation is genuinely uncertain. Waiting for perfect evidence might mean missing a protective window during midlife when biomarker changes could still be reversed. But starting a long-term supplement regimen based on mouse studies and biomarker associations carries the risk of time, cost, and potential side effects with unproven benefit. Reasonable approaches include discussing supplement use with a neurologist or memory specialist who can weigh individual risk factors, ensuring any supplements don’t interact with current medications, and prioritizing the interventions with strongest human evidence—Mediterranean diet patterns, cognitive engagement, sleep quality, and cardiovascular health.

The Future of Supplement-Based Prevention

The supplement research landscape is likely to shift substantially over the next five to ten years. Multiple human trials are now underway testing NAD+ precursors, lithium microdosing, and vitamin D supplementation at various doses and durations in older adults. These studies will measure not just biomarker changes but actual cognitive outcomes over years of treatment, which is what ultimately matters for prevention. If any supplement shows meaningful slowing of cognitive decline in a well-designed human trial, it could transform preventive Alzheimer’s care and make these approaches standard recommendations.

The reality is that Alzheimer’s prevention will likely require multiple approaches rather than a single supplement solution. The disease arises from the intersection of genetics, aging, vascular function, inflammatory status, protein metabolism, and environmental exposures. A supplement that addresses one mechanism—such as NAD+ restoration or tau stabilization—might provide incomplete protection when used alone but meaningful protection when combined with other lifestyle and pharmaceutical interventions. The most promising research direction may ultimately involve personalized combinations based on individual biomarker profiles rather than one-size-fits-all supplementation.

Conclusion

Recent research on vitamin D, NAD+, lithium, and arginine has revealed multiple pathways through which supplements might protect against Alzheimer’s disease biomarkers. Studies show vitamin D associated with lower tau accumulation, NAD+ reversing disease markers in mice, lithium protecting neurons, and arginine reducing inflammation and plaques. These findings have generated legitimate scientific interest and suggest that targeting fundamental aging processes in the brain might be viable prevention strategies. However, the critical caveat is that biomarker changes in animals have not yet translated to demonstrated cognitive protection in human trials.

The responsible approach involves acknowledging both the promise and the uncertainty. If you’re concerned about dementia risk, discussing supplement options with a neurologist or memory specialist can help you weigh the plausibility of these approaches against your individual risk factors and health status. Meanwhile, continuing to pursue interventions with stronger human evidence—cardiovascular health, cognitive engagement, sleep optimization, Mediterranean dietary patterns—remains the most evidence-based foundation for cognitive aging. The supplement research is moving in an encouraging direction, but we’re still in the phase of careful investigation rather than confident recommendation.