May 2016 Issue
Nutrition's Impact on Parkinson's Disease
By Matt Ruscigno, MPH, RD
Vol. 18 No. 5 P. 42
Evidence suggests proper nutrition may help alleviate the debilitating symptoms associated with this neurodegenerative condition.
Parkinson's disease is a progressive degenerative disorder affecting the central nervous system, primarily the motor system, due to decreased dopamine, a neurotransmitter in the brain. Dopamine connects thoughts about movement to muscle activity. Therefore, when dopamine is reduced, the first systems affected are movement-related: shaking, instability, tremors, slowness, rigidity, and difficulty walking. There's no known cause of Parkinson's disease, but it's understood that chronic neuroinflammation exacerbates the loss of the dopaminergic neurons.1
Actor Michael J. Fox is a prominent face of the disease and has appeared on TV and in front of Congress unmedicated to show the severity of these physical symptoms. Behavioral limitations also appear in later stages as well as dementia, which is also a neurodegenerative disorder commonly found in older patients with Parkinson's disease. Sleep issues and depression also may be present.
While the disease was first described nearly 200 years ago by James Parkinson, MD, diagnosis remains difficult and is based on the classification of the patient's symptoms. As many as 1 million Americans may have Parkinson's disease,2 and there are approximately 60,000 new cases per year that exact a total cost of nearly $25 billion, including lost wages, according to the Parkinson's Disease Foundation.3 Despite this significant impact, research on Parkinson's disease is somewhat limited, and current findings are inconclusive. But for the motivated nutrition professional, there are several dietary interventions that can be recommended to patients to possibly alleviate disease symptoms and otherwise maintain a healthful quality of life.
Potential Causes and Nutritional Considerations for Prevention
Since no known cause of Parkinson's disease exists, identifying clear preventative measures remains elusive. There are some curious positive associations in the research including pesticide exposure, living in rural areas, and being white.4 Inversely related is a diet high in plant foods, coffee consumption (possibly for men only), exercise, and tobacco use.5 The protective effect of tobacco is curious and has spawned research on the potential benefits of consuming tobacco-related plants, like peppers, which is discussed below.
Environmental Factors and Toxins
According to the National Institutes of Health, genetics may play a small role in the onset of Parkinson's disease, but most researchers "believe environmental exposures increase a person's risk of developing the disease."6 Pesticides, heavy metals, and polychlorinated biphenyls (PCBs) are all being studied for a potential association with the development of Parkinson's. PCBs are synthetic chemicals primarily used as coolants and insulators in electrical equipment. Despite having been banned for several decades, they persist in the environment due to a long half-life. A study in Neurotoxicology found that PCB levels were significantly elevated in postmortem brain tissue of patients with Parkinson's disease compared with controls.7 The findings were especially significant in women. The researchers concluded, "Persistence of these compounds in the brain provides the cumulative and toxicokinetic features indicative of chronically acting neurotoxicants."
Potential Dietary Sources of Toxins
No one food or food group has been conclusively linked to Parkinson's disease, but there's some evidence relating certain foods with its development. Some fish, including salmon, are a source of ß-methylamino-L-alanine, a neurotoxic nonprotein amino acid that may be causative in neurodegenerative diseases like Parkinson's.8 Exposure to pesticides also may be a risk factor, but the research at this point hasn't determined which ones, or what levels, are causative.9 Organic foods have lower pesticide residues than their conventionally grown equivalents, but the evidence isn't strong enough to recommend organic foods for the prevention or treatment of Parkinson's disease.10
Research shows that pesticides can accumulate in other foods. Using the Cancer Prevention Study II Nutrition Cohort, researchers from the Harvard School of Public Health found a positive association with dairy consumption.11 The risk of Parkinson's disease in those who consumed the most dairy was higher for men than women. These findings are consistent with prospective data from both the Health Professionals Follow-up Study and the Nurses' Health Study. No association was found with calcium consumption (those taking supplements didn't have increased risk) or other nutrients. Dairy products can contain small amounts of bioaccumulated pesticides and neurotoxins, and speculation abounds concerning this potential mechanism in Parkinson's disease development. The authors also consider the relationship between high dairy consumption and lower circulating levels of uric acid. Uric acid is neuroprotective and may reduce oxidative damage; reduced levels may be related to Parkinson's.
Coffee and Caffeine Connection
An exhaustive review and meta-analysis examined 26 studies in 2012 and found a 25% risk reduction for Parkinson's disease among caffeine consumers, with stronger results for men than women.12 One study found a dose-dependent response, with those consuming the most coffee (10 cups per day) having the most protection.13 A 2016 review paper in Parkinson's Disease reported that both epidemiologic and clinical studies paint a comprehensive picture of the anti-Parkinsonian potential of caffeine.14
Peppers and … Tobacco?
Tobacco has far too many health risks to ever be recommended, but there's clear evidence that cigarette smoking is protective against Parkinson's disease.15 These findings have led to further research in the broader tobacco family—the Solanaceae family of nightshade plants. A study from the University of Washington found that peppers—not overall vegetable consumption—were inversely related to Parkinson's disease.16 Edible plants in the Solanaceae family do contain small amounts of nicotine, but the researchers were quick to note there isn't enough evidence to conclude that the nicotine is responsible.
Flavonoids and Plant Foods
Another study from the Harvard School of Public Health found that those who consumed the most flavonoids in the form of anthocyanin-rich foods like blueberries and black raspberries were 40% less likely to develop Parkinson's disease.17 Lead researcher Xiang Gao, MD, PhD, says, "Flavonoids may be a natural and healthy way to reduce your risk of developing Parkinson's disease." A diet high in whole plant foods, which naturally contain significant amounts of phytochemicals like flavonoids, also is protective.18
Nutrition Guidelines for Patients
Once a Parkinson's disease diagnosis is made, proper nutrition is important for minimizing associated symptoms and delaying disease progression. Heather Zwickey, PhD, dean of research and a professor of immunology at the National College of Natural Medicine, has a three-part strategy for developing a healthful diet protective against Parkinson's.19 She says food choices should be neuroprotective, anti-inflammatory, and antioxidant-rich. Nuts like walnuts, pistachios, and Brazils nuts are especially neuroprotective, Zwickey says. Recommended anti-inflammatory foods include leafy greens and soy products. Antioxidants are found in the most colorful plant foods, such as berries.
Antioxidant-rich and caffeine-containing green tea is recommended for patients with Parkinson's disease. There's some evidence that green tea also may be protective in the development of Parkinson's.20 Interestingly, fava beans contain levodopa, a precursor to dopamine in the brain, in a significant enough amount to be beneficial for those with Parkinson's. Fava beans also contain beneficial antioxidants and fiber; the importance of the latter is discussed below.21,22 Dairy products should be reduced or eliminated because they decrease uric acid. If patients are accustomed to consuming dairy products, dietitians can recommend nut-based alternatives for milk, cheese, and ice cream.
According to the Academy of Nutrition and Dietetics, the goals for patients are to reduce constipation, maintain hydration status, assess for dysphagia and gastrointestinal (GI) problems, provide adequate energy, and prevent bone thinning and vitamin D deficiency.23
Fiber Intake and Reducing Constipation
Parkinson's disease can impact all bodily movements, including the GI tract. Insoluble fiber can help move food along the GI tract and reduce constipation. Whole grains such as brown rice, rye, barley, and quinoa are excellent sources of insoluble fiber and also contain vitamin E, which has antioxidant activity. Starchy vegetables and legumes, especially lima beans and lentils, are good sources, as are berries. These foods should be added to the diet slowly to give the GI tract time to adjust to the effects of fiber.
Drinking enough fluid is independently important and will additionally alleviate constipation. Some patients may experience decreased thirst and should develop a plan to maintain adequate fluid intake. Carrying a water bottle and setting daily, specific goals for water drinking can help. Fruits and vegetables also are hydrating and can be a source for water-averse patients.
Some patients may have trouble swallowing due to involuntary muscle movements that make food consumption difficult. Since swallowing is compromised, food or liquid can get into the lungs and may cause aspiration pneumonia, the leading cause of death in Parkinson's disease.24 It's imperative to recognize changes early in swallowing ability so a patient's diet can be adjusted accordingly to avoid aspiration pneumonia and malnutrition. RDs can work with a patient's medical team, specifically a speech-language pathologist, if available, to create a nutrition plan that works within a patient's limitations. In some cases, enteral feeding may become a necessity.
Weight Loss and Weight Gain
Patients with Parkinson's may be underweight because of eating difficulties or overweight due to the inability to exercise. Dietitians can provide nutrition counseling to help patients lose or maintain a healthful weight. Fruits, vegetables, whole grains, and legumes are nutrient-dense and can aid in weight loss by increasing satiety with fewer calories. Nuts and nut-based foods are calorically dense and palatable and can be recommended for underweight patients. Although engaging in physical activity may be difficult, modifications can be made for individuals as a tool in weight maintenance. In addition, exercise, as tolerated, can play a substantial role in improving patients' quality of life. Some research shows that vigorous exercise can have a neuroprotective effect25 and has pharmacological benefits independent of weight loss or cardiovascular benefits.26
Bone Thinning and Vitamin D Deficiency
Limited exercise and a low-quality diet can lead to poor vitamin D status and decreased bone density in patients with Parkinson's disease. Dietitians must check for adequate calcium consumption. Green leafy vegetables contain calcium, fiber, and beneficial antioxidants. A supplement for calcium and vitamin D may be indicated. Weight-bearing exercise is also important for bone health. Patients may have a physical therapist on their health care team who can determine which exercises are appropriate. If they don't, dietitians can recommend they consult with one.
Drug-Nutrient Interaction and Protein Timing
The main medication prescribed to patients with Parkinson's disease is levodopa, a protein building block that competes for absorption with other proteins. It's recommended that protein be limited throughout the day to reduce interaction with levodopa. Carbohydrate-rich snacks may be necessary with levodopa to prevent nausea. At dinnertime, more protein-rich foods can be added to ensure adequate intake.
There are many unknowns concerning the prevention and treatment of Parkinson's disease, but this shouldn't dissuade dietitians from utilizing good nutrition practices. While there's no guarantee that eating a diet high in fiber and antioxidant-rich plant foods is effective in relieving constipation or reducing symptoms of Parkinson's, there are virtually no negative side effects of introducing them. A patient with Parkinson's may be unaware of nutrition's role in their treatment plan, which gives the RD an excellent opportunity for providing nutrition education. Preventing malnutrition and aspiration pneumonia should be a priority, and an interdisciplinary approach may be necessary.
— Matt Ruscigno, MPH, RD, is the past chair of the Vegetarian Nutrition Dietetic Practice Group of the Academy of Nutrition and Dietetics. He's the coauthor of No Meat Athlete and Appetite for Reduction and has a private practice in Los Angeles.
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