Parkinson’s disease (PD) is among the most common chronic neurodegenerative conditions, affecting 1% of those over 60 years of age, and involves motor and non-motor impairments. Alterations in normal physiology may become apparent years – in some cases, 10–20 years – before established diagnostic criteria are met. Thus, better clinical outcomes may result when practitioners utilize nutritional and supplement interventions that support reductions in neuroinflammation and neurodegeneration as early as possible. PD is a devastating, progressive neurodegenerative condition that has both hereditary and environmental components to its pathogenesis, and early identification of risk factors and onset is critical. The purpose of this review is to highlight various nutrition and supplement interventions that may positively affect disease onset and progression, and that warrant further research.
Parkinson’s disease (PD) was initially referred to as “shaking palsy” by Dr. James Parkinson in 1817. It is among the most common chronic neurodegenerative conditions, affecting 1% of those over 60 years of age,1 and involves motor and non-motor impairments. Manifestations of motor-related impairments include symptoms such as resting tremor, bradykinesia, and muscular rigidity. The pathogenesis of the motor-related symptoms of PD involves the loss of striatal dopaminergic neurons, which decreases the amount of dopamine released, while the pathogenesis of non-motor symptoms encompasses aberrations in adenosine and enkephalins, and the loss of neurons comprising the glutaminergic, cholinergic, serotonergic, and adrenergic systems.2,3
Furthermore, histological studies indicate that alpha-synuclein (α-Syn) aggregates in neuronal perikaryal and neuronal processes to form Lewy bodies and Lewy neurites, respectively.4 Another pathophysiological change that is prominent and may play a role in the early identification of PD is mitochondrial dysfunction. Research indicates that the aggregation of α-Syn in the mitochondria of individuals with PD damages mitochondrial complex I, which leads to iron accumulation causing the production of reactive oxygen species (ROS) and subsequent oxidative stress.5,6 Damage to mitochondrial complex IV (i.e. cytochrome c oxidase) also appears to be evident in individuals with PD.7,8 Such mitochondrial damage decreases energy production in dopaminergic neurons and may increase the generation of ROS, causing oxidative stress that damages lipids, cell proteins, and DNA – ultimately, leading to neuronal cell death and neuroinflammation.6,8,9
Alterations in normal physiology may become apparent 10–20 years before established diagnostic criteria are met.10 Some of these earlier alterations include motor function impairments (e.g. tremor, balance issues), autonomic dysregulation (e.g. constipation, hypotension, erectile dysfunction, dizziness), neuropsychiatric conditions (e.g. depression, anxiety), and other imbalances (e.g. fatigue, anosmia, sleep disturbances, handwriting changes, mood swings, dysphagia, drooling).11 Of note, evidence reveals that degeneration from PD occurs first in the gastrointestinal system and then in the brain.12 Thus, better clinical outcomes may result when practitioners identify early indications of PD with or without a diagnosis,10,11 allowing for nutritional, supplement, and lifestyle interventions that support reductions in neuroinflammation and neurodegeneration. Some of these potential interventions are discussed in detail below.
POSSIBLE NUTRITIONAL INTERVENTIONS
WHOLE FOODS DIET
Studies suggest that a whole foods dietary pattern that focuses on a diverse array of vegetables, low-sugar fruits, healthy fat intake, quality proteins, and complex carbohydrates may positively influence mitochondrial and neuronal integrity and both motor and non-motor functions, while also potentially protecting against inflammation, oxidative stress, and neurodegeneration.13 Additionally, certain herbs and spices may increase the neuroprotective benefits of such a diet.14 A diet that provides anti-oxidants, fatty acids, and B vitamins (including folate) may facilitate lowering the risk of neurodegeneration, neuroinflammation, PD,15,16 cognitive decline, and dementia.17 Research also suggests that such potentially anti-inflammatory dietary components improve neutralization of excessive ROS and reactive nitrogen species (RNS) associated with cognitive and motor impairments in neurodegenerative diseases.18,19
Findings from a variety of epidemiological and nutrient-related studies guide tailoring the anti-inflammatory diet to best meet the needs of individuals with PD. Some of the nutrients and food groups that research suggests may positively affect neural pathways that support synaptic plasticity include omega-3 fatty acids, curcumin, flavonoids, B vitamins, vitamin D, vitamin E, choline, antioxidant combinations, and selenium.20
POTENTIALLY BENEFICIAL FOODS AND BIOACTIVE SUBSTANCES
NIGHTSHADES AND NICOTINE
Individuals with PD may benefit from consuming nightshade vegetables, including tomatoes, eggplant, peppers, and potatoes. The naturally occurring nicotine and other compounds in nightshade vegetables may reduce the risk of PD.23 The purported mechanisms involve attenuating nigrostriatal damage, and reductions in dyskinesias resulting from L-DOPA, tremor, and rigidity have been observed.24 Despite these promising findings, it should be noted that the research is inconclusive.23
Green tea, which is a rich source of polyphenols – especially epigallocatechin-3-gallate (EGCG) and theaflavins – confers neuroprotective and neuroregenerative effects. In vitro and animal studies have shown that the polyphenols in green tea regulate intracellular signaling pathways and prevent α-Syn accumulation, which protects against and delays PD onset. Such mechanisms broaden the polyphenols’ anti-oxidant, anti-inflammatory, and transition metal chelating effects, removing a source of neuroinflammation.27–30 Very high caffeine intake should be avoided with monoamine oxidase type B (MAO-B) inhibitors, as this combination may cause a hypertensive crisis.
Red wine, which is high in phenolic compounds (e.g. quercetin, myricetin, resveratrol, catechins, tannins, and anthocyanidins), has shown neuroprotective effects in both in vitro and in vivo PD models. These include anti-inflammatory, anti-oxidant, free-radical scavenging, metal chelating, and cell signaling pathway modulatory properties.31 As alcohol use disorder may increase the risk of PD,32 individuals who do not already drink red wine in moderation, or who have issues with alcohol should refrain from consuming this alcoholic beverage. Instead, these individuals would benefit from finding a comparable source of polyphenols. In addition, alcohol is contraindicated with dopamine agonists, catechol-o-methyl transferase (COMT) inhibitors, and some other PD-related medications.
Another particularly beneficial compound for individuals with PD is caffeine. Roshan et al.33 suggest three to four cups of caffeinated coffee (about 200 mg) per day. Caffeine intake must be timed carefully, however, to avoid exacerbating sleep issues. It also may not be appropriate for slow caffeine metabolizers. Research suggests that caffeine acts as an adenosine (A2) receptor antagonist. Interestingly, the highest concentrations of this receptor type are found in the basal ganglia. A proposed mechanism of action for caffeine is that it inhibits astrocyte-related inflammatory processes in a manner that promotes excitation in the basal ganglia.33 Furthermore, caffeine demonstrates an ability to maintain blood–brain barrier (BBB) integrity, which may otherwise be compromised in PD.34 That said, Lee et al.35 posit that coffee’s neuroprotective effect is due to quercetin, not caffeine. Very high caffeine intake should be avoided with MAO-B inhibitors, as this combination may cause a hypertensive crisis.
Individuals with PD exhibit dysbiotic gut microbiomes: notably a decrease in Prevotella that correlates with motor-related symptoms,36 and an increase in Enterobacteriaceae, which is associated with postural and gait abnormalities.36,37 Eating foods rich in prebiotic carbohydrates such as Jerusalem artichokes, onions, garlic, leeks, dandelion greens, asparagus, chicory root, bananas, cocoa, and nuts will help increase the population of Prevotella in the gut, and support improved motor function.38,39 Given that evidence suggests disruptions in the intestinal barrier and gut microbiome are involved in PD pathogenesis,37,40 it is significant that many foods and bioactive substances mentioned in this paper help enhance immune function by preventing micronutrient deficiencies; reducing inflammation;41,42 and supporting a healthy intestinal barrier43 and gut microbiome.44
FOODS, FOOD GROUPS, AND SUBSTANCES TO ELIMINATE
Certain foods, food groups, and substances may contribute to or exacerbate PD symptoms. Eliminating them could prove to be an important component of an anti-inflammatory diet.
Dairy often contains pesticide residues,45 which have been associated with PD and disease progression.15,46,47 Moreover, dairy breaks down uric acid. As a neuroprotective anti-oxidant, uric acid minimizes oxidative damage by neutralizing ROS, RNS, and the damaging peroxynitrite molecule in the central nervous system (CNS).15,46 Individuals with PD often have reduced levels of uric acid.15 Eliminating dairy may prevent further break down of these already low levels.46 Dairy may also contribute to insulin resistance and the development of “type III diabetes,” an emerging condition associated with neurodegenerative diseases.15
Individuals with PD often have increased intestinal permeability, which may play a role in the development of this disease.40,48 Dairy products such as cow’s milk may cause hypersensitivity reactions in some individuals, which results in intestinal inflammation and increased intestinal permeability. Specifically, dairy protein may act as an antigen that initiates a Th1 immune response.49 The resulting increase in tumor necrosis factor-alpha (TNF-α) degrades tight junctions in the intestinal epithelium, leading to increased intestinal permeability. Immunogenic lipopolysaccharide (LPS) can then enter systemic circulation, causing the chronic production of pro-inflammatory cytokines.48,50 Pro-inflammatory cytokines such as interleukin (IL)-1, IL-6, and TNF-α increase BBB permeability. The ROS characteristic of systemic inflammation can also increase BBB permeability. As a result, systemically circulating α-Syn can enter the CNS, trigger a neuroinflammatory response, and further expose the CNS to neurotoxic chemicals.48,51
TRANS FATTY ACIDS
HIGH-FRUCTOSE CORN SYRUP AND REFINED SUGAR
High-fructose corn syrup (HFCS) has been shown to contain the neurotoxin mercury.54 Research also suggests that fructose disturbs gene networks responsible for neuronal and central metabolic modulatory processes. This provides insight into the potential epigenetic effects that link fructose consumption to metabolic and neurologic dysfunctions.55 Both HFCS and refined sugar may contribute to the development of insulin resistance and diabetes,56,57 conditions that are associated with an increased risk of developing PD.58,59 Identifying food sources of HFCS is not always easy, but many foods contain them, making it important to read food labels.60
While there is much debate about the safety profile of artificial sweeteners such as aspartame, sucralose, acesulfame-K, and saccharine,61 evidence suggests that they and their accompanying metabolites may have neurotoxic effects.62,63 It is also possible that artificial sweeteners alter neurotransmitter synthesis and release, as well as inducing oxidative stress.64 In addition, studies have found that artificial sweeteners and sugar substitutes such as xylitol can increase Bifidobacteria in the gut. People with PD often have higher levels of Bifidobacteria in the first place.65,66 The relationship between artificial sweetener intake and neurodegenerative conditions is, however, inconsistent.62,67
Multiple supplements may complement a personalized diet for individuals with PD. Supplementation and dosages should always be considered in the context of an individual’s diet, medications, and health condition. For the following supplements, the PD medications that were researched for potential contraindications include:
Anti-Parkinson’s agents: carbidopa, levodopa, Sinemet
Dopamine agonists: Mirapex, Requip, Neupro, Apokyn
MAO-B inhibitors: Eldepryl, Zelapar, Azilect, Xadago
COMT inhibitors: Comtan
Decreased mitochondrial coenzyme Q10 (CoQ10) levels are frequently found in individuals with PD. In complexes I and II of mitochondria, CoQ10 accepts electrons.68 However, studies administering 200–1200 mg of CoQ10 per day to individuals with PD demonstrate inconsistent results – some suggest higher dosages yield the best outcomes, while others found that comparable outcomes were found with lower dosages.69–72 There are no known contraindications with the PD medications listed.
Individuals with PD tend to exhibit decreased glutathione concentrations in the substantia nigra, where dopaminergic neurons are often lost.73–75 N-acetylcysteine, the precursor to glutathione, can cross the BBB. This anti-oxidant supports endogenous glutathione production, including intraneuronal glutathione,76 to protect against oxidative stress and mitochondrial damage. A daily dose of at least 600 mg is advised. An optimal oral dosage is currently undergoing research, with one phase 2 clinical trial (https://clinicaltrials.gov/ct2/show/NCT02212678) utilizing 6000 mg/day, and a completed phase 1/2 trial (https://clinicaltrials.gov/ct2/show/NCT01470027) demonstrating the benefit of 1800 mg and 3600 mg/day. There are no known contraindications with the PD medications listed.
Vitamin D acts as a neuro-immunomodulator.79 Findings from one study showed that low serum 25-hydroxyvitamin D levels are associated with an increased risk of developing PD. In this study, after adjusting for confounding variables, individuals who had a 50 nmol/l or higher serum 25-hydroxyvitamin D level had a risk of PD that was 65% lower than individuals who had levels below 25 nmol/l.80 There are no known contraindications with the PD medications listed.
The antioxidant properties of curcumin may be particularly beneficial for individuals with PD as a component of an anti-inflammatory diet. In vitro experiments indicate that curcumin helps minimize reduced glutathione concentrations resulting from oxidative stress in dopaminergic cells .81 In addition, an in vitro α-Syn model has also shown that curcumin decreases α-Syn aggregation.82 A 400 mg daily dose could be beneficial, but bioavailability will vary based upon formulation and adjuvants. There are no known contraindications with the PD medications listed.
MUCUNA PRURIENS (COWAGE)
Ayurvedic medicine uses the seeds from the legume M. pruriens, a naturally occurring botanical source of levodopa, as a PD treatment. Studies suggest that the M. pruriens seeds and the traditional lab-created levodopa differ pharmacokinetically and that, unlike levodopa, the seeds from M. pruriens confer neuroprotective effects.83 Of note, a finding that a HP-200 M. pruriens endocarp preparation improved Parkinsonism symptomatology but did not influence dopamine metabolism to an appreciable extent, implies that other constituents in the botanical (i.e. not levodopa) may be responsible for the benefits of M. pruriens in individuals with PD.84 Current research suggests both low and high doses demonstrate efficacy.85 There are no known contraindications with the PD medications listed.
While PD is a devastating, progressive neurodegenerative condition that has both hereditary and environmental components to its pathogenesis, multiple nutrition and supplement interventions show promise for positively affecting disease onset and progression. To intervene as early as possible, clinicians should assess vitamin D status, vitamin B12 status, oxidative stress, inflammation, essential fatty acid status, insulin resistance, BBB integrity, intestinal integrity, and gut microbiome health.
Earlier identification of risk factors and PD onset (i.e. pre-motor PD), could result in better outcomes. Further research is warranted to determine whether personalized, PD-targeted anti-inflammatory and neuroprotective nutrition, and supplementation may protect against neurodegeneration and optimize the quality of life for individuals with this condition.
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