Advances in Nutraceutical Approaches for Alzheimer’s Disease: Clinical Insights and Emerging Therapies

Historical Background

The story of Alzheimer’s disease (AD) begins over a century ago. In 1906, Alois Alzheimer, a German psychiatrist and neuropathologist, reported the peculiar case of Auguste D., a 51-year-old woman who had developed progressive memory loss, disorientation, and hallucinations. At autopsy, Alzheimer observed dramatic atrophy of the cerebral cortex alongside the abnormal presence of amyloid plaques and neurofibrillary tangles, two features that would later become diagnostic cornerstones [1]. Just a few years later, Emil Kraepelin included this case in the eighth edition of his textbook Psychiatrie and named the condition “Alzheimer’s disease,” thus placing it in medical history as a distinct entity [2]. These early accounts remain striking not only because they shaped our definition of dementia but also because they anticipated the molecular discoveries that unfolded many decades later.

Epidemiology and Global Burden

More than a century after its first description, AD has become the leading cause of dementia worldwide. The steady rise in life expectancy has expanded the at-risk population, particularly in societies with aging demographics. The World Alzheimer Report 2025 estimates that over 55 million people currently live with dementia, and AD accounts for the majority of these cases. The global cost of dementia care has now exceeded US $1.3 trillion and is predicted to nearly double by 2030 if no effective interventions are developed [3]. Beyond numbers, the disease exerts tremendous strain on families, communities, and healthcare systems. Care provision is especially challenging in low- and middle-income countries, where formal medical infrastructure is often lacking. In such settings, caregiving falls disproportionately on family members, amplifying both economic and psychosocial consequences [4]. This dual burden economic costs coupled with hidden caregiving labor makes AD not just a neurological disorder but a societal challenge with wide-reaching implications.

Clinical Subtypes of Alzheimer’s Disease

AD is not a uniform condition, and clinicians recognize distinct subtypes depending on the age at onset.

1. Early-Onset Alzheimer’s Disease (EOAD)

This manifests before the age of 65 and, while rare, is clinically important. These cases are often linked to inherited genetic mutations in the APP, PSEN1, and PSEN2 genes. Patients typically present with atypical symptoms visual disturbances, language problems, or executive dysfunction rather than isolated memory loss. Progression is usually rapid, and the impact on working-age individuals and their families is devastating [5].

2. Late-Onset Alzheimer’s Disease (LOAD)

The much more common form, LOAD, appears after age 65. Its incidence rises steeply with advancing age, doubling approximately every five years between ages 60 and 85 [6]. LOAD is driven by multifactorial influences aging itself, lifestyle choices, and genetic risk factors such as the APOE ε4 allele. Because of its high prevalence, LOAD accounts for most of the global dementia burden [3]. While less predictable than EOAD in presentation, LOAD dominates the epidemiological landscape and represents the primary target for therapeutic research.

Clinical Manifestations

The symptomatic course of AD reflects gradual but relentless decline.

1. Memory and cognition

The earliest and most recognizable deficit is episodic memory loss. Patients first struggle to recall recent conversations or events, but over time, impairments extend to reasoning, judgment, and problem-solving. Everyday activities such as managing finances or organizing tasks become difficult. Eventually, even long-term memories erode, leaving individuals profoundly disoriented [7].

2. Language and communication

Language difficulties follow, often manifesting as word-finding problems or incomplete sentences. Later, comprehension falters and speech becomes fragmented or incoherent. This linguistic decline severely restricts social interaction and creates barriers between patients and caregivers [8].

3. Neuropsychiatric symptoms

AD is not solely a cognitive disorder. A broad spectrum of behavioural and psychological symptoms (BPSD) complicates the clinical picture. Depression, apathy, aggression, agitation, and disordered sleep are all common [9]. These manifestations often appear early and worsen over time. Importantly, they accelerate cognitive decline, drive caregiver stress, and are a leading cause of institutionalization [10].

4. Functional Decline

Over the years, functional decline becomes inevitable. At first, patients require assistance with complex tasks such as managing medication or transportation. Later, even basic self-care eating, bathing, dressing requires supervision. By the advanced stage, complete dependence on caregivers is the rule, underscoring the devastating toll of the disease [11].

Diagnostic Approaches

Diagnosis has advanced considerably over the past two decades. A multimodal strategy combining clinical evaluation, biomarker assessment, and neuroimaging now provides far greater accuracy than was previously possible.

1. Neuropsychological tools

Cognitive screening remains the entry point. Widely used tools include the Mini-Mental State Examination and the Montreal Cognitive Assessment. These instruments measure orientation, attention, recall, and language, but they lack specificity for AD and cannot reliably differentiate it from other dementias [12].

2. Cerebrospinal fluid biomarkers

Lumbar puncture analysis of cerebrospinal fluid (CSF) has proven highly informative. A typical AD profile consists of decreased Aβ42 and elevated tau proteins, reflecting amyloid plaque accumulation and neurofibrillary tangle formation. These biomarkers allow clinicians to detect AD with far greater sensitivity, even before overt clinical symptoms develop [6,7].

3. Neuroimaging advances

Magnetic resonance imaging (MRI) often reveals hippocampal atrophy, while fluorodeoxyglucose positron emission tomography (FDG-PET) shows hypometabolism in temporoparietal regions. In recent years, amyloid and tau PET tracers have provided direct visualization of pathological deposits, bringing new clarity to diagnosis and staging [8].

4. Frameworks and staging

The 2018 NIA-AA research framework redefined AD using a biological approach. This “AT(N)” model Amyloid, Tau, and Neurodegeneration classifies patients on the basis of biomarker evidence rather than clinical symptoms alone [9]. In 2024, the Alzheimer’s Association revised its criteria to incorporate emerging blood-based biomarkers, which promise earlier, less invasive diagnosis [10]. Despite these advances, neuropathology remains the gold standard: postmortem examination consistently confirms amyloid plaques and neurofibrillary tangles as defining lesions [11].

Perspectives and Unmet Needs

Despite progress in diagnostics, therapeutic options remain limited. Approved medications can only modestly alleviate symptoms and do not halt neurodegeneration. Research over the past decade has broadened our understanding of genetic and molecular mechanisms, but effective disease-modifying therapies remain elusive. Biomarkers, neuroimaging, and advances in personalized medicine, however, offer cautious optimism. By integrating these approaches into clinical practice, earlier detection and targeted therapies may eventually transform AD care. Until then, the disease continues to impose an enormous emotional, financial, and societal burden that demands urgent scientific and policy attention.

CAUSES AND RISK FACTORS

Genetic factors

Apolipoprotein E ε4 (APOE ε4) remains the most powerful genetic risk factor for late-onset AD. Meta-analyses show that individuals with one ε4 allele have approximately 2–3 times increased risk, while homozygotes may reach up to 12–15 times risk compared to non-carriers [13,14]. However, genetic predisposition is not destiny: many carriers never develop AD, and disease prevalence varies across populations for example, despite high ε4 frequency, some Nigerian populations exhibit lower AD incidence, suggesting gene-environment modifiers at play [15].

Early-onset familial forms are rare but devastating. Mutations in APP, PSEN1, and PSEN2 genes cause pathological processing of amyloid precursor protein, increasing Aβ generation and accelerating neurodegeneration. Though these cases account for less than 5% of total AD, their study has illuminated core disease mechanisms [16,17].

Age-related mechanisms

Aging is more than a number it acts as a biological accelerator. Over the decades, neurons accumulate oxidative damage from reactive oxygen species, which compromise proteins, lipids, and DNA. In parallel, mitochondrial dysfunction undermines energy production essential for synaptic health. The result is a fragile neural network vulnerable to degeneration [18,19]. Recent studies also emphasize how mitochondrial fragmentation and disturbed proteostasis contribute to synaptic loss, while dysregulated microglia and neuroinflammation further amplify neuronal injury [20].

Lifestyle influences

Lifestyle choices carry considerable weight in Alzheimer’s risk. According to a 2024 Lancet Commission report, addressing 14 modifiable risk factors such as hypertension, smoking, obesity, hearing impairment, and high midlife LDL cholesterol could prevent or delay up to 45% of dementia cases globally [21]. Particularly notable is the role of high cholesterol, newly recognized as contributing to about 7% of dementia risk [21].

Nutritional patterns matter too. Diets rich in anti-inflammatory and antioxidant foods such as the Mediterranean or MIND dietary patterns are associated with significantly reduced AD risk, even in APOE ε4 carriers [22]. Physical inactivity, smoking, untreated hypertension, and diabetes impose additional risk through vascular and inflammatory pathways [21,23]. Moreover, emerging evidence shows that sensory deficits like hearing and vision impairment, as well as social isolation, amplify dementia risk, partly by reducing cognitive reserve the brain’s resilience to pathology [21,24].

Environmental and exogenous factors

Environmental exposures inflict long-term harm on brain health. Accumulating studies implicate heavy metals such as aluminium, lead, copper, and arsenic as agents that elevate oxidative stress, disrupt Aβ metabolism, and promote neuroinflammation [25]. Similarly, long-term exposure to air pollution has been associated with incremental dementia risk, though exact mechanisms remain under investigation [21].

Traumatic brain injury (TBI) continues to be a well-recognized factor that increases risk. Meta-analyses estimate that moderate-to-severe head injury raises AD risk significantly even years later likely via tauopathy acceleration,   blood–brain   barrier   disruption,   and   chronic   neuroinflammation   [26,27]. AD arises from an interplay of genetic, age-related, lifestyle, and environmental factors, each supported by varying levels of evidence, as summarized in Table 1.

TABLE 1. MAJOR CAUSES AND RISK FACTORS ASSOCIATED WITH ALZHEIMER’S DISEASE, WITH SUPPORTING EVIDENCE.

Neuropsychiatric complications

Neuropsychiatric symptoms (NPS) are highly prevalent in AD, affecting nearly all patients over the disease course [28]. Common NPS include depression, anxiety, psychosis, agitation, aggression, and apathy [29]. Depression manifests as persistent sadness, loss of interest, and low energy, accelerating cognitive decline and increasing mortality risk [30]. Psychosis and agitation, characterized by hallucinations, delusions, and restlessness, complicate caregiving and often require pharmacologic or behavioural interventions [31].

Physical complications

Physical health is frequently compromised in AD patients. Malnutrition affects a substantial proportion of individuals, with studies reporting prevalence rates ranging from 6.8% to 75% [32,33]. Nutritional deficits exacerbate neurodegeneration by reducing neurotransmitter synthesis and brain energy availability. Frailty, often intertwined with malnutrition, diminishes functional reserve and increases vulnerability to falls, hospitalization, and mortality [34,35]. Falls are particularly dangerous, leading to fractures, prolonged hospitalization, and accelerated cognitive decline [36].

Social complications

AD exerts a profound social impact, largely through caregiver burden and increased rates of institutionalization. Family members and informal caregivers often experience stress, anxiety, depression, and physical health decline due to the long-term demands of care [37,38]. Institutionalization becomes necessary as the disease progresses, driven by severe cognitive and behavioural symptoms or caregiver inability to provide adequate care at home [39]. These social complications often create a feedback loop, where caregiver stress and inadequate support further compromise patient outcomes.

Economic and public health perspective

AD places significant financial burdens on healthcare systems and society as a whole. Direct medical costs are substantial, with billions spent annually on treatments, hospitalizations, and long-term care [40]. Unpaid caregiver contributions also represent a significant societal cost, totalling hundreds of billions per year globally [41]. Projections indicate that by 2030, the global economic burden of dementia will surpass $2 trillion, highlighting the urgent need for public health interventions and policy planning [42]. Beyond financial costs, AD represents a major public health challenge, affecting workforce participation, social services, and healthcare infrastructure.

PATHOPHYSIOLOGY OF THE DISEASE

Amyloid cascade hypothesis (Aβ plaques).

AD begins years before symptoms, with abnormal amyloid-β (Aβ) production/clearance leading to extracellular plaques. Contemporary multimodal and proteomic studies support an “Aβ-first” sequence in which early Aβ dysmetabolism facilitates downstream tauopathy and neurodegeneration, even while debate about sufficiency of amyloid persists [43,44,45]. Recent human cohort studies indicate that early cortical amyloid-beta (Aβ) accumulation interacts synergistically with emerging tau pathology to disrupt neurophysiological function and serve as predictors of subsequent cognitive decline. These findings support a primary albeit not exclusive role for Aβ in the pathogenic cascade [44]. Additionally, plasma biomarkers indicative of insoluble tau, seeded by upstream Aβ accumulation, further connect the molecular cascade to accessible peripheral biological measures [46].

Tau pathology (neurofibrillary tangles).

Hyperphosphorylated tau aggregates into paired helical filaments and neurofibrillary tangles (NFTs) that track closely with symptom severity and anatomical spread. Recent work underscores that Aβ “permits” or accelerates trans-neocortical propagation of tau, while tau burden aligns more tightly than Aβ with synaptic failure and clinical stage [43,44,45]. Blood-based MTBR-tau243, reflecting insoluble tangle load, now mirrors PET/CSF measures and prognosticates progression, positioning tau as the proximate driver of neuronal dysfunction after Aβ priming [46].

Neuroinflammation and microglial activation.

Microglia initially buffer pathology by clearing Aβ; chronic activation transitions to a pro-inflammatory, complement-tagging state that promotes synapse loss and fuels tau spread. High-impact syntheses delineate cytokine, inflammasome, and complement signalling that connect innate immunity to both plaques and tangles [47]. Mechanistic studies identify perivascular SPP1 cause microglia into phagocytic, synapse-engulfing phenotypes near amyloid deposits further offering a tractable axis for intervention [48]. TREM2-pathway augmentation enhances microglial metabolism and plaque compaction in vivo, illustrating disease-modifying potential of immune reprogramming [49].

Cholinergic deficit and synaptic dysfunction.

Degeneration of basal forebrain cholinergic neurons especially the nucleus basalis of Meynert emerges early and predicts downstream entorhinal and cortical atrophy, linking neurotransmitter loss to network vulnerability [50,51]. Contemporary reviews argue the cholinergic system intersects with amyloid-tau models through selective vulnerability, attentional network disruption, and trans-synaptic spread [50]. Synapse-centric evidence indicates that presynaptic and postsynaptic injury correlates strongly with cognitive decline than global atrophy, highlighting synaptic integrity as a critical therapeutic target [52]. Large-scale human datasets now connect glial reactivity to CSF synaptic biomarkers and map network-constrained synaptic loss modulated by phosphorylated tau [53,54].

Oxidative stress and mitochondrial impairment.

Redox imbalance, impaired mitophagy, and bioenergetic failure amplify both amyloidogenesis and tau phosphorylation, creating a self-reinforcing loop with inflammation and synaptic injury. Recent reviews integrate mitochondrial dynamics, defective quality control, and genome instability as upstream amplifiers of AD pathology, with convergent effects on neuronal resilience and cognitive decline [55,56]. Vascular-metabolic coupling failures (early cerebral blood-flow changes, calcium dysregulation) likely interact with mitochondrial stress before overt neuron loss, aligning with preclinical stages of the disease [57].

Collectively, AD pathogenesis reflects an interconnected network Aβ initiation, tau propagation, innate- immune dysregulation, neurotransmitter and synaptic failure, and oxidative-mitochondrial stress offering multiple, complementary targets for nutraceutical modulation as illustrated schematically in Figure1.

FIGURE 1. PATHOPHYSIOLOGICAL MECHANISMS OF ALZHEIMER’S DISEASE

ALLOPATHIC REMEDIES

Current pharmacological management of AD focuses on symptomatic relief and, more recently, attempts at disease modification. The principal classes of agents are outlined below.

Acetylcholinesterase (AChE) inhibitors

These represent the first-line approach. These drugs (donepezil, rivastigmine, galantamine) block acetylcholine degradation, partially compensating for cholinergic neuronal loss and improving cognition and daily functioning [58,59]. Beyond symptomatic relief, AChE may interact with amyloid-β (Aβ), suggesting a pathogenic role, though this remains under investigation [60].

N-methyl-D-aspartate (NMDA) receptor antagonists

Most notably memantine, act by dampening excitotoxic glutamatergic signalling, which contributes to neuronal death in AD. Memantine, a non-competitive NMDA blocker, is FDA-approved and provides modest benefits in moderate-to-severe AD, often used alone or in combination with AChE inhibitors [61,62,63]. Recent trials are exploring dual-acting compounds with both cholinergic and glutamatergic effects.

Anti-amyloid monoclonal antibodies

These mark a shift toward disease-modifying strategies. Aducanumab, Lecanemab, and Donanemab target aggregated Aβ, promoting clearance. Lecanemab received FDA approval in 2023 after demonstrating slowed cognitive decline in phase 3 trials, while Donanemab reported positive outcomes in 2023–2024 clinical studies [64,65,66]. Despite regulatory approvals, their high cost, modest efficacy, and risks such as amyloid-related imaging abnormalities (ARIA) have generated debate [67].

Anti-tau therapies

Tau aggregation inhibitors and antisense oligonucleotides are under early-phase evaluation, aiming to reduce neurofibrillary tangles and slow disease progression [68].

Symptomatic agents

Agents such as antidepressants and antipsychotics are often prescribed for behavioural and psychological symptoms of dementia, though they do not alter disease trajectory and must be used cautiously due to safety concerns [69].

Collectively, while symptomatic therapies remain standard, recent advances in monoclonal antibodies and tau- targeted strategies represent the first steps toward modifying the underlying disease process.

A schematic overview of the major allopathic drug classes used in AD is presented in Figure 2, which summarizes both approved and emerging therapeutic categories [70].

FIGURE 2. CLASSIFICATION OF ALLOPATHIC DRUGS USED IN ALZHEIMER’S DISEASE

NUTRACEUTICAL MANAGEMENT AND ADVANCES

Multinutrient formulations

1. Clinical evidence from Souvenaid (Fortasyn Connect)

Fortasyn Connect, a proprietary multinutrient blend of omega-3 fatty acids, uridine monophosphate, phospholipids, choline, B vitamins, antioxidants, and selenium, has been tested extensively under the trade name Souvenaid. The LipiDiDiet trial first demonstrated its potential in patients with prodromal AD, showing slower decline on memory composite scores over two years compared with placebo [71]. Later follow-ups extended to 36 months indicated that Souvenaid reduced hippocampal atrophy and delayed clinical progression toward dementia [72]. Importantly, benefits were most consistent in patients at the very earliest symptomatic stages, suggesting a window of therapeutic responsiveness.

Other randomized studies, such as the S-Connect trial in mild-to-moderate AD, did not demonstrate robust cognitive improvement, highlighting the variability of effects depending on disease stage [73]. More recently, pooled analyses across trials have shown significant but modest effects on Clinical Dementia Rating–Sum of Boxes (CDR-SB) outcomes [74]. These data support the idea that Fortasyn Connect may function best as a preventive or prodromal intervention rather than as a therapy for advanced AD.

2. Cognitive, functional, and biomarker outcomes

Along with cognitive function, Souvenaid has been linked to measurable alterations in neurobiological biomarkers, indicating potential underlying effects on neural integrity and synaptic health. In the LipiDiDiet study, participants receiving the formulation displayed reduced hippocampal volume loss on MRI and attenuated ventricular enlargement compared with placebo [72]. Plasma biomarkers also suggested improved homocysteine regulation, likely linked to its B-vitamin components [75]. Functional benefits, though more variable, included slower decline in daily living activities in long-term follow-up analyses [74].

Mechanistically, the formulation enhances neuronal membrane phospholipid synthesis and synaptic density, as evidenced by magnetic resonance spectroscopy studies [76]. This synaptic support is consistent with preclinical data showing increased dendritic spine density in animal models exposed to similar nutrient combinations. While not curative, these findings point to a disease-modifying potential through preservation of structural and synaptic integrity.

3. Safety and tolerability

Across trials, Souvenaid has demonstrated a favourable safety profile. Adverse events such as mild gastrointestinal discomfort were comparable to placebo, with no significant laboratory abnormalities or cardiovascular risks reported [71,73,74]. This contrasts with many pharmacological AD treatments, where systemic side effects limit long-term adherence. Importantly, adherence in Souvenaid studies has generally been high, reflecting its acceptability as a daily nutritional drink.

Still, questions remain. Critics argue that the magnitude of benefit is modest and may not justify routine use outside clinical trials. Moreover, Souvenaid’s classification as a medical food, rather than a drug, complicates regulatory oversight and standardization. Despite these limitations, its excellent tolerability and consistent signals of benefit in early disease provide a strong rationale for further research, particularly in combination with lifestyle or pharmacological interventions.

Probiotics and Synbiotics

1. Gut–brain axis and mechanistic insights

The gut–brain axis has emerged as a critical modulator of neurodegenerative disorders, including AD. Dysbiosis alters microbial metabolites, increases intestinal permeability, and promotes systemic inflammation, all of which accelerate amyloid deposition and tau phosphorylation [77]. Preclinical models show that probiotic supplementation can restore microbiota composition, reduce neuroinflammation, and enhance synaptic plasticity [78]. These effects are mediated partly through modulation of vagal signaling and immune pathways, suggesting that probiotics act beyond the gut to influence central nervous system homeostasis.

2. Clinical trial evidences

Several clinical trials have evaluated the impact of probiotics on cognition in AD. In a significant randomized controlled trial, Akbari et al. (2016) demonstrated that a 12-week probiotic milk intervention improved Mini- Mental State Examination scores in patients with severe AD compared to placebo [79]. More recently, Tamtaji et al. (2019) reported that multi-strain probiotics combined with selenium supplementation improved both cognitive performance and metabolic status in AD patients [80].

Meta-analyses have reinforced these findings, showing modest but consistent cognitive benefits with probiotics and synbiotics, particularly on Mini-Mental State Examination and AD Assessment Scale–Cognitive Subscale (ADAS-Cog) [81]. However, outcomes appear strain-specific, with Lactobacillus and Bifidobacterium genera being most consistently effective [82]. These data indicate that while probiotics are not yet disease-modifying, they may offer clinically relevant symptomatic benefits.

3. Role of short-chain fatty acids and neuroinflammation

One mechanistic pathway linking gut microbes to AD involves short-chain fatty acids (SCFAs) such as butyrate, acetate, and propionate. SCFAs regulate blood–brain barrier integrity, microglial activation, and histone acetylation, thereby influencing neuroinflammatory tone [83]. In AD models, butyrate supplementation reduced amyloid pathology and improved memory, underscoring the therapeutic potential of targeting microbial metabolites [78]. Clinical data remain preliminary, but stool metabolomic analyses in AD patients reveal reduced SCFA levels, consistent with gut dysbiosis [84].

Thus, probiotics and synbiotics may exert cognitive benefits partly by restoring SCFA balance, reducing neuroinflammation, and maintaining neuronal resilience. Future precision trials that stratify participants by baseline microbiome composition may clarify which patients are most likely to benefit.

Saffron

1. Comparative trials with donepezil and memantine

Clinical interest in Crocus sativus (saffron) for AD arose from small but well-controlled randomized trials conducted in Iran. A 22-week, double-blind RCT compared 30 mg/day saffron extract with 10 mg/day donepezil in patients with mild-to-moderate AD and found comparable improvements on cognitive measures and similar overall adverse-event rates, though vomiting was more frequent with donepezil [85]. In a separate 12-month randomized trial of patients with moderate-to-severe AD, 30 mg/day saffron capsules produced cognitive outcomes comparable to memantine (20 mg/day) on standardized scales, suggesting non-inferiority in that cohort [86]. These head-to-head studies are small and were performed in single geographic regions, so while intriguing they require larger, multicenter confirmation.

2. Effects on cognition and behaviour

Meta-analytic syntheses and narrative reviews conclude that saffron produces modest but consistent cognitive improvements versus placebo and similar efficacy compared with standard AD drugs in the limited trials available [87,88]. Improvements have been detected on common scales such as ADAS-Cog and MMSE, and some studies report parallel gains in clinician-rated global function. Mechanistic preclinical work supports biological plausibility: saffron constituents (crocin, crocetin, safranal) reduce oxidative stress, inhibit Aβ aggregation, and modulate glutamatergic signaling mechanisms that align with observed clinical effects [89]. Still, effect sizes across trials are moderate and likely dependent on disease stage, dose, and formulation.

3. Safety and tolerability profile

Across randomized trials and pooled reviews, saffron has a favourable safety profile. Adverse events are generally mild and transient (e.g., gastrointestinal upset), and serious adverse events have not been consistently observed at clinical doses (20–30 mg/day) used in trials [85,86,87]. Notably, saffron was associated with fewer cholinergic side effects (nausea, vomiting) than donepezil in the comparative trial, which may enhance tolerability in some patients [85]. However, long-term safety data remain limited, and heterogeneity in extract standardization and dosing underscores the need for regulatory standardization and larger surveillance studies [90].

Medium-chain triglycerides (MCTs) and ketogenic interventions

1. Rationale for MCTs and Ketogenic Strategies in AD

The rationale for medium-chain triglycerides (MCTs) and ketogenic interventions in AD rests on the observation that declining cerebral glucose utilization can be partly offset by ketone bodies β-hydroxybutyrate and acetoacetate as alternative energy substrates. MCTs, particularly caprylic and capric triglycerides, are rapidly metabolized in the liver to generate circulating ketones without requiring full dietary carbohydrate restriction. This principle has been applied in investigational medical foods such as Axona® (AC-1202, caprylic triglyceride) and in ketogenic MCT drinks providing around 30 g/day, both of which aim to enhance neuronal energy supply under conditions of impaired glucose metabolism [91,92].

2. Evidence and Genotype-Dependent Effects

Randomized trials show mixed but instructive results. In a 90-day, multicenter RCT of AC-1202 (n=152), the active group improved on ADAS-Cog by ~1.9 points vs placebo at day 45 in the intention-to-treat cohort (p=0.0235) and larger differences in per-protocol analyses; importantly, APOE ε4-negative participants gained much larger improvements (e.g., 4.77-point ADAS-Cog benefit at day 45, p=0.0005), indicating a strong genotype-dependent effect [93]. An earlier crossover study using a single oral MCT dose showed acute increases in plasma β-hydroxybutyrate and improved ADAS-Cog performance in APOE4(−) but not APOE4(+) subjects (P≈0.04) [94].

3. Cognitive Benefits in MCI and Imaging Correlates

Larger and longer interventions with ketogenic MCT drinks have extended these findings into mild cognitive impairment (MCI). A 6-month RCT of 30 g/day kMCT (a ketogenic supplement) in MCI (n=52) increased brain ketone uptake by ~230% (p<0.001) and produced improvements in episodic memory, language, and processing speed versus baseline; cognitive gains correlated with ketone uptake on PET [95]. Follow-up trials and imaging studies also report improved white-matter energy supply and processing speed with kMCT supplementation [96].

4. Safety, Tolerability, and Future Research Needs

Systematic reviews and meta-analyses (2020–2024) conclude that MCT/ketone interventions can improve some cognitive outcomes, but effects are moderate, heterogeneous, and more consistent in APOE ε4-negative individuals; several recent pooled analyses report larger standardized mean differences in APOE4(−) subgroups and call for better-powered, genotype-stratified RCTs [97,98]. Adverse events are generally gastrointestinal (diarrhea, bloating) and dose-dependent; tolerability improves with gradual dose titration.

In sum, MCTs and ketogenic supplements provide a biologically plausible, low-risk means to bypass brain glucose deficits and can enhance cognition in selected patients (notably APOE4 negatives and those with MCI). The field now needs larger, longer, genotype-stratified trials and head-to-head comparisons of dietary MCT, kMCT supplements, and full ketogenic diets to define optimal candidates, doses, and durability of benefit.

Curcumin and polyphenols

1. Neuroprotective Potential

Turmeric, a spice central to Indian cooking, contains curcumin a polyphenol that has long intrigued Alzheimer’s researchers. Beyond its culinary role, curcumin interacts with amyloid and tau pathology, dampens oxidative stress, and calms neuroinflammation. These multi-level effects mirror what has been observed in cell and animal models, where turmeric extracts reduced plaque deposition and preserved neuronal function [99,100]. Similar neuroprotective hints come from other dietary polyphenols, including resveratrol from red wine and grapes, as well as green tea catechins like epigallocatechin gallate (EGCG), each of which engages multiple disease pathways [101].

2. Challenges in Bioavailability and Delivery Systems

One immediate obstacle was apparent: the amount of curcumin that reaches the brain from eating turmeric in curry is very limited. Its poor solubility and rapid metabolism mean that, despite millennia of culinary use, therapeutic benefits in AD are unlikely without improved delivery systems. In response, scientists have designed more bioavailable forms such as curcumin-phospholipid complexes and nanoparticle dispersions. A drinkable formulation based on nanoparticles called Theracurmin® increases systemic exposure by more than twenty times as compared to turmeric powder used in the kitchen [102].

3. Trial Outcomes and Biological Effects

Clinical trials offer cautious optimism. In healthy older adults followed for 18 months, daily Theracurmin® led to nearly 30% improvement in verbal memory scores, while attention also improved significantly over placebo [103]. But translation to patients with AD has been less robust. In one randomized study, individuals receiving curcumin capsules showed no meaningful cognitive advantage on MMSE or ADAS-Cog, though blood amyloid levels dropped, suggesting a biological effect without clear clinical expression [104].

4. Meta-Analyses and Future Perspectives

Across meta-analyses, the pattern repeats: these compounds are safe, often well tolerated even at gram doses, and biologically active but the impact on cognition remains inconsistent [105]. Whether turmeric in diet, resveratrol in moderate wine intake, or green tea catechins can serve as preventive measures is still debated, but the evolving picture suggests that delivery technology and patient selection (e.g., early vs late disease) may determine whether these natural molecules move from kitchen staples to genuine disease-modifying agents.

NAD+ precursors (e.g., nicotinamide riboside, NMN)

1. Role in Brain Health

NAD? is an essential coenzyme, critical for mitochondrial energy production, DNA repair, and redox balance. Its decline with age is well documented and appears to be accelerated in AD, where metabolic failure and synaptic stress dominate the pathology [106,107]. Boosting NAD? levels through precursors like nicotinamide riboside (NR) or nicotinamide mononucleotide (NMN) is therefore emerging as a nutraceutical strategy aimed at restoring neuronal resilience.

2. Dietary Sources and Early Human Research

Food-derived niacin sources such as tuna, salmon, mushrooms, peanuts, and green vegetables naturally contribute to NAD? biosynthesis, though in far lower doses than the concentrated supplements tested clinically. This dietary baseline may partially explain why populations consuming niacin-rich diets tend to show slower rates of age-related cognitive decline in observational studies [108].

Human supplementation studies are still early stage. Martens et al. (2018) reported that NR raised circulating NAD? metabolites and reduced inflammatory cytokines in older adults, although cognitive outcomes were not directly assessed [109]. In metabolic cohorts, Dollerup et al. (2018) found improved muscle mitochondrial respiration with NR, highlighting systemic benefits that could indirectly support brain function [110]. Meanwhile, phosphorus magnetic resonance spectroscopy (31P-MRS) imaging showed subtle increases in cerebral NAD? after NR intake in healthy adults, suggesting central nervous system penetration [111].

3. Clinical Developments and Future Outlook

Clinical momentum is building. Yoshino et al. (2021) demonstrated that NMN improved insulin sensitivity and muscle mitochondrial metabolism in prediabetic adults [112], while Hou et al. (2021) noted favourable biomarker shifts pointing toward reduced vascular inflammation [113]. Trials now underway are testing whether NAD? augmentation can slow conversion from mild cognitive impairment to dementia, with APOE ε4 carriers receiving particular focus.

For now, the attraction lies in strong mechanistic rationale, safe supplementation profile, and potential synergy with diet. Whether niacin-rich foods alone or high-dose precursors in capsule form, maintaining NAD? pools could represent a metabolic “insurance policy” against cognitive decline. Definitive evidence, however, will depend on biomarker-driven, long-term trials that directly track amyloid, tau, and cognitive trajectories.

VITAMINS AND DIETARY COFACTORS

1. B-complex Vitamins and Homocysteine-lowering Trials

Homocysteine has long been tied to brain shrinkage and memory decline, which prompted researchers to ask whether giving high-dose B vitamins could help. In the VITACOG study, Smith et al. (2010) tested folate (0.8 mg), B12 (0.5 mg), and B6 (20 mg) in older adults with mild cognitive impairment. The results were striking on MRI: average brain shrinkage slowed by about 30%, and in those with high baseline homocysteine the effect was even greater, nearly halving atrophy rates [114]. Later work by Douaud et al. (2013) showed these changes were concentrated in regions vulnerable to Alzheimer’s, while Oulhaj et al. (2016) noted that people with good omega-3 status benefited most [115,116]. That said, Clarke et al. (2014) pooled data from ~22,000 people and saw almost no effect on memory tests across the general population [117]. In other words, B vitamins clearly shift biology, but the cognitive impact may depend heavily on who you treat.

2. Vitamin E and Antioxidant Mechanisms

Vitamin E has perhaps the most mixed track record. In the TEAM-AD study, Dysken et al. (2014) reported that 2,000 IU/day α-tocopherol slowed decline in patients with mild–moderate AD by nearly 20% per year, translating into about a six-month delay in clinical worsening [118]. Families also reported reduced caregiving time. But safety worries cloud the picture: Miller et al. (2005) suggested that long-term high-dose use (≥400 IU/day) might slightly increase mortality risk [119]. For that reason, vitamin E is best viewed as a potential adjunct in carefully selected patients rather than a general preventive strategy.

3. Vitamin D and Neurocognition

Observational studies consistently link low vitamin D levels with higher dementia risk. For example, Ghahremani et al. (2023) reported about a 40% lower incidence of dementia in supplement users, while Llewellyn et al. (2010) showed that severe deficiency was associated with nearly double the risk [121,122]. In contrast, randomized evidence has been less convincing: Manson et al. (2019), testing 2,000 IU/day in the large VITAL trial, found no measurable short-term cognitive improvement [120]. Mechanistically, vitamin D receptors are expressed in neurons and glia, and the compound exerts anti-inflammatory and neurotrophic effects, but for now the practical approach is to correct deficiency without expecting robust memory gains from routine supplementation.

Collectively, nutraceuticals demonstrate multi-target actions in AD, spanning amyloid and tau modulation, neuroinflammation, synaptic support, oxidative stress, mitochondrial resilience, and metabolic compensation. These relationships are summarized schematically in Figure 3.

FIGURE 3. NUTRACEUTICAL STRATEGIES IN ALZHEIMER’S DISEASE

As depicted in Figure 3, nutraceutical strategies in AD act through multiple converging pathways, including amyloid and tau modulation, neuroinflammation, synaptic preservation, and mitochondrial support. Building on these mechanistic insights, the strength of evidence from clinical trials varies considerably across different interventions. A consolidated overview of trial outcomes covering cognition, function, and biomarker endpoints is presented in Table 2.

TABLE 2. SUMMARY OF CLINICAL TRIAL EVIDENCE FOR NUTRACEUTICALS IN ALZHEIMER’S DISEASE.

While key trials provide evidence of modest clinical benefits with nutraceuticals, understanding their biological plausibility is equally important. Several interventions have been investigated not only for symptomatic improvements but also for their effects on disease-related biomarkers and mechanistic pathways. Multinutrient formulations, for instance, show MRI and MRS evidence of synaptic support; probiotics influence systemic inflammation and gut-derived metabolites; saffron demonstrates antioxidant and anti-amyloid effects in both clinical and preclinical studies; and medium-chain triglycerides enhance ketone utilization, improving cerebral energy metabolism. Similarly, B-vitamins and vitamin D impact homocysteine levels and neuroendocrine pathways, whereas NAD? precursors and curcumin target mitochondrial function and protein aggregation. A consolidated  overview  of  these  mechanistic  and  biomarker  findings  is  presented  in  Table 3.

TABLE 3.  MECHANISTIC AND BIOMARKER SUPPORT FOR NUTRACEUTICAL INTERVENTIONS IN ALZHEIMER’S DISEASE.