Learning Outcomes
By the end of this section, you should be able to:
- 5.1.1 Recognize the normal function of the neurologic system.
- 5.1.2 Recognize cues of nutritional impact on the neurologic system.
- 5.1.3 Analyze cues of nutritional impact on the neurologic system.
Normal Function of the Neurologic System
The neurologic system is defined by its two major components: the central nervous system (CNS), consisting of the brain and the spinal cord, and the peripheral nervous system (PNS), consisting of all neurons outside of the CNS. The PNS includes the somatic nervous system, which facilitates movement and muscle control in the body; the neuromuscular junctions, which are located at the terminal end of motor nerves and conduct impulses to target muscles; and the autonomic nervous system, which regulates involuntary body processes such as blood pressure, heart rate, respiration, digestion, and sexual arousal.
The autonomic nervous system is composed of the sympathetic and parasympathetic nervous systems. The sympathetic nervous system identifies impending danger and stimulates motor activity to either stay put and defend against the danger or to run away from the danger, known as the fight-or-flight response. The parasympathetic nervous system signals the body to rest and recover, as well as to digest food intake, known as the “rest-and-digest” response.
While the CNS is responsible for regulating cardiac, skeletal, and visceral smooth muscle activity, the PNS relays sensory input to the CNS for processing and then relays this information via motor responses to various effector organs and cells of the body. The PNS has two components: The afferent (sensory) component transmits impulses from peripheral organs to the CNS, and the efferent (motor) component transmits impulses from the CNS out to peripheral organs to initiate an active response or action.
The brain requires approximately 20% of the body’s total oxygen delivery and about 15% of the cardiac output. Because the brain cannot store glucose, it must rely on a constant supply of nutrients from the arterial blood flow, at a rate of 50–55 mL/g/min (Norris, 2019).
Normal Brain Structure and Function
The brain conducts the most complex functions in the human body and is responsible for a person’s intelligence, memory, speech, behavioral responses to stress, heart rate regulation, breathing rates, and movement. However, it weighs approximately 3 lb (Figure 5.2). Approximately 60% of the brain is composed of fat, and the remaining 40% is made up of water, carbohydrates, protein, and various salts. The brain contains nerves (neurons and glial cells) as well as blood vessels, which supply the nutrients required for effective brain function. The tissue of the brain is composed of cells referred to as white matter, located in the central part of the brain, and gray matter, located on the external portion of the brain.
The internal white matter of the brain is composed of axons, the long slender projections of neurons, which conduct electrical impulses across nerve cells. Axons are wrapped in myelin, a white fatty protein coating that protects and insulates the axon and increases the speed of impulse conduction to other sensory and motor cells of the nervous system. The gray matter is composed mainly of the round cell bodies (soma) of the neurons, which give it its grayish color; it is responsible for interpreting and processing information as it is received. As information is processed, the gray matter sends and receives chemical and electrical signals to control various processes such as movements and sensations. The cerebrum is the largest part of the brain, weighing 1.5–3 lb or about 2% of the total body weight. It is responsible for initiating, coordinating, and regulating movement, body temperature, speech, judgment, thinking, learning, reasoning, and emotions, as well as functions of the senses, such as vision, hearing, and touch. The various lobes of the cerebrum include the frontal, temporal, parietal, and occipital lobes, each controlling specific functions.
The protective outer layer of the cerebrum is the cerebral cortex. It facilitates memory, thinking, learning, reasoning, problem-solving, emotions, consciousness, and sensory functions. It is divided into two hemispheres, with the corpus callosum providing a pathway for communication between these two sides of the brain.
The brainstem has three components: the midbrain (responsible for hearing, movement, and other responses to the environment), the pons (responsible for blinking, vision, balance, hearing, facial expression, chewing, and tear production), and the medulla (responsible for heart rhythm, regulation of oxygen and carbon dioxide levels, blood flow, and reflexive responses such as coughing, swallowing, sneezing, and vomiting). The spinal cord carries sensory and motor messages to and from the brain to the effector organs to control bodily functions and environmental responses.
The cerebellum is responsible for posture, equilibrium, and balance, as well as playing a role in emotions and social behavior. The cerebellum may also have a role in addiction, autism, and some psychiatric conditions.
Neurotransmitters
The neurons (nerve cells) are the functional cells of the neurologic system and relay all sensory and motor information via a complex system of chemicals produced by the body called neurotransmitters (Figure 5.3). They can be categorized into three groups:
- Amino acids that function in the CNS synapses (Gamma-aminobutyric acid [GABA], glycine, and glutamic acid)
- Peptides that perceive pain and various sensations (endorphins and enkephalins)
- Monoamines that transmit in the autonomic nervous system (epinephrine and norepinephrine)
Neurotransmitters allow neurons to communicate by relaying excitatory or inhibitory messages at the synapse of the neuron to perform a wide range of functions via action potentials. Neurons have the capability to open the sodium channels along the cell membranes, allowing sodium to move into the cell, thus creating cellular depolarization, and subsequently moving potassium out of the cell in a process called the action potential. In turn, the cell then repolarizes, producing a resting state called the resting membrane potential. These actions enable the nervous system to rapidly transmit messages to and from the brain and tissues of the body, allowing changes for adaptation to the external or internal environment.
Assessment of Nutrition and the Function of the Neurologic System
A comprehensive nutrition assessment is performed as a routine component of neurologic assessment during the intake assessment. All clients require initial and ongoing screenings by nurses to determine any nutritional risk factors related to proper functioning of the neurologic system. When performing a general neurologic assessment, the nurse should begin by determining the client’s level of consciousness, mental status, motor abilities and balance, and sensation. The nurse should take a detailed history of medical conditions directly affecting the client or the client’s biological family. Any history of alcohol intake, medications, and dietary supplements, either prescribed or over the counter, should be included. A history of pain, both recent and past, should be explored. Pain related to chewing or swallowing, gastrointestinal pain, or pain that interferes with feeding may be pertinent to a nutritional problem, and mealtime observations can provide information regarding overall nutritional risk. Any history of visual disturbances, disequilibrium, dizziness, vertigo, vomiting, or changes in weight are significant and could be related to dehydration or the quantity and quality of caloric and nutritional intake.
Guidelines for assessing weight, height, and body mass index (BMI) have been published by the National Heart, Lung and Blood Institute (2023). A weight loss of more than 10% over the past year or 5% within the previous 6 months is significant and should be explored. Specifically, the nurse should ask for details of the client’s self-management practices, including dietary, urinary, and bowel patterns; allergies; exercise and activities; and usual sleep cycle. A BMI of 30 or higher is associated with greater risks for neurologic and cardiovascular diseases (Centers for Disease Control and Prevention, 2022; Held et al., 2022). If the client is not critically ill, anthropometric measurements, midarm muscle circumference, and skinfold thickness measurements should be recorded because these may be helpful for estimating percentages of body fat and lean body muscle as a measure of nutritional status and general health. For clients who are determined to be at nutritional risk, a referral should be established with a registered dietitian.
An evaluation of mental health is an important component of neurologic health and should include an expression of the client’s self-concept and perception, as well as a summary of patterns related to adaptation to daily life stressors and relationships. This evaluation should also include specific beliefs or cultural norms as they relate to nutritional health practices. A history of diseases, health conditions, and medications is extremely useful for determining possible nutritional deficiencies. Given the sensitive nature of dietary habits, it is helpful for the nurse to maintain a nonthreatening and consistent approach to nutritional screening as it relates to neurologic health.
Clinical Tip
Therapeutic Conversation
When performing evaluations, the nurse should conduct conversation using therapeutic conversation, such as the five As (assess, advise, agree, assist, and arrange). Motivational interviewing is another strategy that is helpful in engaging clients who may be hesitant.
Small changes are generally advised when considering behavioral changes that can seem overwhelming to the client. Dietary changes such as reducing or increasing the intake of certain foods slowly can have a dramatic effect over the long term. It is important to allow small substitutions that allow for individualized treats that satisfy food cravings while reducing trans fats and ensuring adequate intake of vegetables and healthy foods. A nursing assessment of nutrition should include a food diary that includes specific questions regarding the client’s dietary habits over the previous few days and months—specifically, the number of meals and snacks consumed each day, the amount of fruit consumed, fluid intake, and fat and sugar intake (Lee, 2022). Nutrition counseling cannot be successfully completed in one meeting. The nurse should plan for subsequent meetings when adjusting a client’s diet and should share the counseling efforts with other members of the health care team.
Controlling Nutrition Status Score
The Controlling Nutritional Status (CONUT) score is an instrument to measure nutrition (Ulíbarri, 2005). A CONUT score is correlated to serum albumin level, the main protein in plasma. Albumin, which is synthesized in the liver, transports hormones and enzymes throughout the body and maintains equilibrium by stabilizing the capillary membrane. Albumin levels may be elevated in individuals who are dehydrated, consume a high-protein diet, or have an acute infection. Albumin levels may also be elevated in clients taking certain medications, such as insulin, steroids, or hormones. Individuals who are malnourished or have liver, kidney, or inflammatory diseases will have low albumin levels. Fasting can rapidly diminish albumin levels by up to one-third within 24–48 hours. Low albumin levels have been linked to increased mortality and longer hospital stay among clients with traumatic brain injury (TBI) because of increased levels of stress, blood loss, and dysphagia (Wang et al., 2020).
The CONUT score presents albumin, lymphocyte, and cholesterol levels as an overall nutritional score (Table 5.1). The formula for the CONUT score is a calculated value: 10 multiplied by the serum albumin value in g/dL, plus 0.005 multiplied by the total lymphocyte count in the peripheral blood in cubic milliliters, plus the total cholesterol score (Wang et al., 2020). The CONUT score may be an indicator of in-hospital mortality and 90-day outcomes in persons with traumatic brain injury (Wang et al., 2020). However, it is important to remember that among clients with acute illness, infection or injury, albumin levels may be reduced due to the acute nature of these pathophysiologic events rather than a nutritional problem. Relying solely on albumin as a marker of nutrition may be inaccurate (Smith, 2017).
| Nutritional Levels in Adults | Normal | Light Deficiency | Moderate Deficiency | Severe Deficiency |
|---|---|---|---|---|
| Serum albumin (g/dL) |
3.5–4.5 | 3.0–3.49 | 2.5–2.99 | < 2.5 |
| Score | 0 | 2 | 4 | 6 |
| Total lymphocytes/mL | > 1600 ≥ 1.600×109/L |
1200–1599 1.200–1.599×109/L |
800–1199 0.800–1.199×109/L |
< 800 < 0.800×109/L |
| Score | 0 | 1 | 2 | 3 |
| Cholesterol (mg/dL) | > 180 | 140–180 | 100–139 | < 100 |
| Score | 0 | 1 | 2 | 3 |
| Total score | 0–1 | 2–4 | 5–8 | 9–12 |
Required Nutrients for Brain Function
The cells of the brain cannot store glucose or other nutrients; as a result, the brain can function for only approximately 10 seconds without depleting the oxygen supply via the cerebral circulation. Glucose is considered a macronutrient and is the main fuel for the brain. Because the neurons in the brain have no capability to store glucose, a continuous supply is required to ensure adequate brain function. Death to brain cells begins when they are deprived of oxygen for only 4–6 minutes. Any disruption in blood flow will lead to a buildup of toxic metabolic byproducts that will damage vulnerable cells in the brain. Other macronutrients that supply the brain with fuel include proteins and fats, which can also act as energy sources.
Micronutrients are vitamins and minerals that are critical for optimal brain function in very small amounts. They include omega-3 fatty acids (important components of the membranes that surround the cells of the body), polyphenols (micronutrients that have health-promoting properties and are found in many fruits and vegetables), vitamins (especially certain B vitamins: B1 [thiamine], B6 [pyridoxine], B9 [folate], and B12), and minerals (zinc, magnesium, iodine, iron).
Zinc is a trace metal ion that contributes to brain health by supporting the immune system and the function of the pituitary hormones, such as the secretion of growth hormone. Zinc has also been shown to increase insulin-like growth factor, which fosters the genesis of neural stem cells, and it has strong antioxidant properties that support immune function (Choi et al., 2020). In addition, zinc accelerates the production of cells that provide nonspecific immunity protection, such as neutrophils and natural killer cells (Choi et al., 2020).
Iodine is a vital mineral micronutrient that stimulates the production of thyroid hormones T3 and T4, which are responsible for brain development and control of cellular metabolism. Iodine is critical to fetal development, as it facilitates neuronal multiplication, migration, and organization; brain development; and nerve cell myelinization. This process continues in the first few years of life. The effect of iodine on the brain continues throughout childhood and adulthood, fostering the ability to learn and the desire and motivation to improve performance (Khattak et al., 2017).
Vitamin B6 is known to reduce levels of homocysteine (an amino acid that can increase inflammation); it stimulates the biosynthesis of certain neurotransmitters such as GABA, dopamine, and serotonin; and it is required for normal development of the CNS during the perinatal period (Smith & Refsum, 2021). Ensuring that the body sustains adequate blood levels of vitamins B6 and B12 has been shown to reduce feelings of stress and depression, improve concentration and memory, and prevent stroke events (Berkins et al., 2021; Smith & Refsum, 2021).
Iron is another essential mineral micronutrient. It facilitates oxygen transportation, DNA synthesis, mitochondrial respiration, myelin production, and the development and metabolism of various neurotransmitters. Iron is received in the brain mainly bound to transferrin on endothelial cells. It crosses the blood–brain barrier and is then released into the extracellular compartments in the brain (Ward et al., 2014).
Magnesium is a dietary micromineral with many roles in the body. A strong body of evidence supports its role in supporting optimal nerve transmission and neuromuscular coordination (Kirkland et al., 2018). Moreover, magnesium has a protective effect against the development of chronic pain, migraine headaches, depression, anxiety, and stroke (Kirkland et al., 2018).
Selenium is a micronutrient that plays an important role as an antioxidant, protecting cells from damage. It is involved in the production of immunoglobins that aid in cellular immunity, as it has anti-inflammatory effects (Farag et al., 2021). During pregnancy, selenium is crucial to mitigate the stress associated with a growing fetus, and selenium deficiency is associated with low birth weight because of restricted intrauterine growth. Clients who are obese before becoming pregnant may have low levels of selenium during the first trimester of pregnancy. The risk of hypertension during pregnancy is increased in clients with selenium deficiency.
Although micronutrients are required in smaller amounts than the macronutrients are, they are essential for most metabolic, biochemical, and regulatory responses of the nervous system (Reddy et al., 2018). See Table 5.2.
| Micronutrient | Expected Effect on Neurologic System | Defined Level | Significance of Abnormal Values | Recommended Daily Allowance and Treatment Dosages |
|---|---|---|---|---|
| Vitamin B1 (thiamine) |
|
|
|
|
| Vitamin B3 (niacin) |
|
|
|
|
| Vitamin B6 (pyridoxine) |
|
|
|
|
| Vitamin B12 (cobalamin) |
|
|
|
|
| Vitamin E |
|
|
|
|
| Copper |
|
|
|
|
| Iodine |
|
Urinary concentrations:
|
|
|
| Magnesium |
|
|
|
|
| Selenium |
|
|
|
|
| Zinc |
|
|
|
|
Given that nearly 60% of brain tissue is composed of fat and that the omega-3 and omega-6 fatty acids account for 20% of the overall brain weight, it is important to understand the role of fats in brain function at all stages of human life. These fatty acids promote cognition, preservation of neurons, and protection against neurodegeneration. This is because omega-3 fatty acids facilitate production of oxyhemoglobin and hemoglobin in the blood, which improve cerebral circulation and subsequently improve overall mental performance (Dighriri et al., 2022).
Another micronutrient group is the polyphenols, which are metabolites of plants. They are potent antioxidants and have long been shown to reduce cardiovascular risk by providing antiplatelet and anti-inflammatory functions. In addition, they may offer some protection from neurodegenerative diseases; recent evidence supports the theory that cognitive decline may be prevented and Alzheimer’s disease may be slowed by the consistent intake of polyphenols (D’Angelo, 2020; Luo et al., 2021). Most plant-based foods contain polyphenols, which can be found in vegetables, fruits, legumes, olive oil, and nuts. Some of the richest sources are colored berries, nuts (especially walnuts, almonds, and hazelnuts), seeds, vegetables, black and green tea, and certain spices. A polyphenol that has received considerable attention over the past decade is curcumin, the root of the turmeric plant (used in many Indian dishes, such as curry), which has shown a dramatic protective effect on the neurologic system. Red wine and dark chocolate have also been shown to contain polyphenols and may be consumed in moderation (Fekete et al., 2023). See Figure 5.4.
Omega-3 Fatty Acids, Protein, and Cholesterol
Various nutrients are critical for ensuring brain health and cerebral blood flow; among the most important are protein, omega-3 fatty acids, and cholesterol. The impact of these nutritional requirements on the neurologic system begins during the prenatal period and extends throughout the lifespan. Omega-3 fatty acids are found in fish, seafood, nuts, seeds, seaweed, spinach, broccoli, and avocados and other colorful fruits and vegetables, as well as in fortified cereals and beverages. They are vital for brain function and can counteract some of the deterioration that can result from brain or spinal cord injury. Recommendations for intake of omega-3 fatty acids range from 0.5 g/day for infants to 1.1–1.6 g/day for persons 51 years of age and older.
Protein is a combination of linked amino acids and is the building block of skeletal muscle. In the neurologic system, protein is required for the adequate function of mitochondria within the nerve cells. Protein deficiency results in leakage of the cell membranes, creating electrolyte disturbances, and has been shown to contribute to neurodegenerative diseases such as stroke, Alzheimer’s disease, and Parkinson’s disease. The current recommendation for adult protein intake is 1.2–1.5 g/kg/day. In the presence of severe illness or injury, more protein intake may be recommended. However, with specific regard to cognition, there are no absolute recommendations for protein intake (Glenn et al., 2019). As mentioned earlier, protein levels in the body are measured by albumin. Prealbumin is the precursor to albumin in the liver and is used by the body to produce other proteins as well. With a half-life of 2–4 days, prealbumin is a highly sensitive indicator of nutritional status. Higher serum levels of albumin have been associated with improved cognitive function in individuals with Parkinson’s disease (Sun et al., 2022). However, stress and inflammation can reduce prealbumin levels and lead to poor outcomes following various neurologic events such as TBI, especially in the presence of an active infection.
The brain maintains the highest level of cholesterol in the body, requiring approximately 20% of the body’s total cholesterol, but the cholesterol level in the brain is independent of cholesterol levels in the peripheral tissues. Cholesterol is a key building block for the creation of myelin. It is found in the astrocytes and other glia cells and is taken up by the neurons as a critical building block to produce hormones (Li et al., 2022). Dietary intake of foods rich in omega-3 fatty acids raise the high-density lipoprotein levels above 40 mg/dL and has been shown to be helpful in preventing dementia, fatigue, “brain fog,” memory loss, depression, and other cognitive problems (Li et al., 2022). Because of the independence of cholesterol metabolism in the brain, measurement of the cholesterol level specifically inside the brain could be an important marker of neurologic health (Jin et al., 2019; Li et al., 2022). For optimal brain health, the current general recommendation is to maintain a total cholesterol level of 160–200 mg/dL (Lee & Siddiqui, 2023).
Assessment of Cerebral Perfusion and Nutrition
Cerebral blood flow is a measured volume of blood flowing per unit of mass over time through the vertebral arteries and internal carotid arteries and is measured as an indirect marker of neuronal function. Although the brain requires a continuous supply of nutrients, it does not have the ability to store them. Therefore, evaluating how well the brain is perfused is an important way to determine brain health. Cerebral perfusion is measured with positron emission tomography (PET) technology to determine the adequacy of blood flow (Chugani, 2021).
Analysis of Nutrition and the Neurologic System
Neuroplasticity, or “the ability of the nervous system to change its activity in response to intrinsic or extrinsic stimuli by reorganizing its structure, functions, or connections” (Mateos-Aparicio & Rodríguez-Moreno, 2019), refers to the brain’s ability to adapt to threats such as brain injury following traumatic or atraumatic injuries and to repair itself. This has led to an increase in studies to explore dietary modifications in neurologic conditions, with a focus on whole foods or food-derivative supplements in the diet.
Although various diet trends—such as paleo, keto, gluten-free, low-carbohydrate, low-cholesterol, pescatarian, low-fat, and vegan diets—have shown benefits in reducing the development of neurologic conditions, these options are discussed less than 12% of the time with health care professionals (Bhat et al., 2019; Roser et al., 2022). Also, because obesity is not considered a disease, many insurance plans do not cover charges for obesity medications or counseling for clients with a BMI of 30 or greater (Dowis & Banga, 2021; Roser et al., 2022).
The adequacy and frequency of dietary nutrition can also affect the blood supply to the brain. For example, the sensation of hunger has been shown to increase cerebral blood flow (CBF) in the hypothalamus, thalamus, amygdala, cerebellum, and other key areas of the brain (Wierenga et al., 2017). Conversely, food intake produces a decrease in CBF in the thalamus, insula, temporal cortex, and cerebellum, but eating causes an increased CBF in the prefrontal cortex, the area that signals satiety of hunger (Wierenga et al., 2017). Some foods have been shown to increase cerebral blood flow in this region, as well as athletic performance, such as beets, red spinach, tart cherries, pomegranate, citrus fruits, walnuts, berries, cinnamon, leafy green vegetables, and other nitrate-rich vegetables (Morris et al., 2018).
Deficiencies of certain fats or toxic levels of some nutrients have been shown to have negative effects on brain health, and dietary intake of trans fats—found in foods such as margarine, fried foods, and commercially prepared cakes, pies, and cookies—has been shown to lead to hypertension and, ultimately, to negatively affect brain health (Harlyjoy et al., 2019).
Nutritional Deficits of Protein, Albumin, and Prealbumin
Malnutrition results from an inadequacy of certain macronutrients and micronutrients and can delay neurologic rehabilitation, leading to increased morbidity and mortality. The deleterious effect of malnutrition is inflammation, which is a precursor to many diseases and conditions. Therefore, an important consideration in the nutritional assessment of neurologic clients is the etiology of any inflammatory process due to any acute or chronic diseases.
An assessment of nutritional status of the neurologic system often includes anthropometric measurements, a nutritional risk assessment, and biomarkers. Specific indicators of malnutrition, such as changes in weight, food intake, loss of body fat or muscle, accumulation of body water, and strength are assessed. Malnutrition is likely if any of these indicators is present. Although no specific nutritional screening tool has been recommended for clients with neurologic disorders, several screening tools that have been successfully used for older clients are suggested for use in persons with neurodegenerative conditions such as dementia, stroke, and Parkinson’s disease (Lee, 2022). Among these tools, the Mini Nutritional Assessment-Short Form (MNA-SF) and the Controlling Nutritional Status (CONUT) tool have been used to assess nutrition in clients with neurologic conditions (Power et al., 2018).
It is estimated that up to 60% of individuals who experience stroke show evidence of malnutrition (Yuan et al., 2021), which contributes to challenges in rehabilitation and readmissions, as well as to overall morbidity and mortality risk. Among clients with neurologic conditions, movement disorders, dysphagia, gastroparesis, cognitive impairment, and depression can all contribute to malnutrition because of decreased oral intake despite an increase in the body’s metabolic needs. Following a stroke or other neurologic event, dysphagia (swallowing difficulty) is common and often results in a delay in resuming nutritional support as the client’s ability to protect their airway during feedings is evaluated. In some cases, enteral feedings are provided via a nasogastric tube or an implanted gastric tube 48–72 hours after the stroke. However, metabolic needs are often accelerated during this period, and early identification of malnutrition can result in improved outcomes (Joundi et al., 2019).
The role of protein in the body is critical in the evaluation of neurologic disorders. The most abundant plasma protein in the body is albumin, which has various antioxidant, anti-inflammatory, and neuroprotective effects. Specifically, albumin has been shown to suppress amyloid formation. Amyloids are proteins that tend to accumulate as tangles and clusters and are associated with a number of conditions, including Alzheimer’s disease. As previously discussed, traditional laboratory markers of malnutrition include the measurement of visceral proteins, namely prealbumin. Prealbumin is protein in the plasma and cerebrospinal fluid that is mainly manufactured in the liver. Prealbumin is considered a transport protein because it carries thyroid hormone and retinol to the liver. It is the precursor of albumin, a transport protein found in the serum, which helps remove small molecules such as bilirubin, calcium, and progesterone in the blood and has a half-life of 20–22 days. Decreased prealbumin levels are linked to protein–calorie malnutrition. Decreased prealbumin levels are often discovered in association with infections and gastrointestinal hemorrhage. Low serum albumin levels in individuals experiencing TBI and other neurologic conditions have been shown to be indicators of poor long-term outcomes, especially among older adults (Liu et al., 2021).
Abnormal Findings Related to Nutrition
The deleterious effects of poor dietary patterns on human cognition continue to plague humans. Neurodegenerative conditions are causing health care costs to soar; for instance, 6.5 million Americans are living with Alzheimer’s disease, and the prevalence is expected to double over the next 30 years (Borshchev et al., 2019). Cognitive deterioration is a concern in many diseases and conditions, and nutrition options, combined with exercise, have been explored as noninvasive strategies to reduce the consequences of neuronal damage. Modifiable risk factors account for 40% of risk factors for Alzheimer’s disease, and diet has been shown to be one of the predominant factors in the development of cognitive decline (Borshchev et al., 2019). Avoidance of some foods, specifically those rich in saturated fats and sugar (often referred to as junk foods), is recommended because they have been shown to contribute to cognitive decline (Borshchev et al., 2019). Other nutritional factors, such as the number of calories consumed per meal and the frequency of food consumption, have been shown to affect cognitive health.
Metabolic syndrome presents a major risk factor for neurologic compromise and is defined as the presence of obesity, dyslipidemia, arterial hypertension, and diabetes. A person is considered obese if their BMI is greater than 30. Dyslipidemia is diagnosed if the total cholesterol level is greater than 200 mg/dL. A total cholesterol level between 200 and 239 is considered borderline high, and a level greater than 240 mg/dL is considered high (CDC, 2022). Arterial hypertension (blood pressure greater than 130/80 mm Hg) has been shown to cause abnormal shifts in cerebral autoregulation, which is the ability of the cerebral vessels to maintain stable blood flow to the brain despite changes in arterial blood pressure (Borshchev, 2019). These shifting patterns seen in persons with metabolic syndrome lead to hypoperfusion and reduced blood flow in the brain and can damage the brain’s white matter (Borshchev, 2019). Although metabolic syndrome is well established as a precursor for diabetes and various cardiovascular ischemic conditions, poor diet combined with obesity has also been associated with cognitive impairment and increased risk for dementia as the individual ages.
Recent evidence has shown that even without metabolic dysfunction, adiposity alone has been shown to potentially accelerate a decline in thought processes, such as attention, intelligence, memory, cognitive flexibility, processing speed, and executive function (Farruggia & Small, 2019; Leigh et al., 2020). Adiposity may also result in reduced brain volume and reduced white matter connectivity, especially in the temporal lobe structures (Leigh et al., 2020). High intake of red meat, processed meat, and fried food and low intake of whole grains have been associated with a reduced level of function in the temporal and frontal lobes, such as memory and executive functions (Leigh et al., 2020). The traditional high-fat Western diet can trigger the advent of Alzheimer’s disease and vascular dementia by triggering inflammation, the development of cerebral vascular atherosclerotic lesions, and a dismantling of the blood–brain barrier (Borshchev et al., 2019; Więckowska-Gacek et al., 2021).
When abnormal cerebral blood flow (the volume of blood that moves through the blood vessels in the brain over a given unit of time) is seen on PET scanning, this can signal overactive or underactive metabolism and can indicate seizure activity, or it can be a marker of ischemic brain injury or degenerative conditions. Food supplementation with polyphenols and omega-3 fatty acids in concert with a supervised nutrition program has been shown to improve cerebral perfusion (Roberts et al., 2020).
Dietary patterns and stress can affect the immune system. As a result, the body may initiate an autoimmune process in which the body perceives normal cells as foreign and attempts to rid the body of a perceived invading substance. In the neurologic system, myelin-producing cells can become affected by this autoimmune process. Myelin can be damaged when the body’s immune cells perceive myelin as a foreign substance and kill the cells that make myelin. The most well-known condition in which myelin is destroyed is multiple sclerosis. Other conditions in which myelin is attacked are optic neuritis and transverse myelitis. Myelin is attacked in the PNS of individuals with Guillain-Barré syndrome, Charcot–Marie–Tooth disorder type 1 or type X, or copper or vitamin B12 deficiency, as well as individuals with infectious processes, excessive alcohol consumption, or intake of certain drugs.
A diet high in saturated fat and sugar is known to produce changes in the gut microbiome, triggering inflammatory processes that alter the immune system, and can lead to cognitive impairment (Leigh et al., 2020). These alterations in the microbiome increase the permeability of the gut and lead to formation of bacterial amyloids (abnormal proteins) and tangles of tau proteins. Tau proteins normally stabilize the tubelike internal skeleton of nerve cells, but when the inflammatory process ignites in the gut, the tau proteins instead become tangled due to phosphorylation in the gut. This phosphorylation then blocks the neuronal transport system and damages vital communication between the neurons, eventually resulting in cell death (Więckowska-Gacek et al., 2021). The most typical neuropathologic changes in the brains of persons with Alzheimer’s disease are these amyloid and tau protein tangles.
Unfolding Case Study
Part A
Read the following clinical scenario and then answer the questions that follow. This case study will evolve throughout the chapter.
The nurse completes a nutritional assessment of Jamal Powell. The client’s past medical history is positive for hypertension, high cholesterol, and obesity.
| Vital Signs | Laboratory Values | |
|---|---|---|
| Temperature: | 98.5°F (36.94°C) | Jamal had blood work drawn the week prior to this visit:
|
| Blood pressure: | 148/90 mm Hg | |
| Heart rate: | 97 beats/min | |
| Respiratory rate: | 14 breaths/min | |
| Oxygen saturation: | 97% on room air | |
| Height: | 5'9" | |
| Weight: | 230 lb (104.33 kg) | |
| BMI: | 34 (Class 1 obesity) | |
Alterations in Micronutrients and Neurologic Health
Deficiencies in micronutrients can contribute to neurologic deterioration. For example, deficiencies in ferrous sulfate and zinc have been associated with ineffective sleep and neurobehavioral problems in young adolescents (Ji et al., 2021). Zinc deficiencies have also been associated with epilepsy, seizures, and deficiency of growth hormone.
Alterations in other micronutrient levels can result in specific neurologic changes. For example, although magnesium serves to promote optimal nerve transmission, low magnesium levels can lead to the death of neurons and contribute to the development of psychiatric problems and other conditions, including depression, anxiety, chronic pain, epilepsy, Alzheimer’s disease, Parkinson’s disease, and stroke.
Selenium improves immunity because of its antioxidant properties, and low levels are associated with tumors, skin conditions, and cardiovascular, neuropsychiatric, and age-related diseases. Iodine deficiency can lead to hypothyroidism, goiter, and mental developmental delays. An iron deficiency can result in worsening heart failure symptoms because iron is key to erythropoietin production. A deficit of iron often results in fatigue and activity intolerance. Copper is essential for maintaining the health of neurons, and an imbalance is associated with neurodegeneration and a variety of neurologic disorders.
Toxic exposure to various substances can also lead to neurologic decline. In someone with a TBI, excessive zinc accumulation can present in the postsynaptic neurons, and this can result in brain damage due to the death of neurons. Therefore, modulation of zinc accumulation may be an important aspect of TBI treatment (Choi et al., 2020).
Heavy metals are minerals with a high molecular weight and are natural elements found in the earth. Due to the nature of these molecules, they cannot be destroyed or degraded. Some of these minerals (including mercury, cadmium, arsenic, chromium, thallium, and lead) can enter the air and the human food and drinking water supply. Heavy metals can accumulate in the body, causing deleterious neurologic effects over time (Choi et al., 2020). The long-term effects of this accumulation can lead to Alzheimer’s disease, Parkinson’s disease, epilepsy, accelerated cognitive decline, and behavioral problems. Mercury exposure can result from eating fish or shellfish that is contaminated or from breathing air contaminated by toxic chemical spills, coal plants, industrial incinerators that burn materials containing mercury, or natural sources such as volcanic eruptions. Exposure to toxic levels of mercury can result in mood swings, tremors, headaches, motor dysfunction, and insomnia.
Cadmium is another heavy metal that may stay in the body for years, although it is eventually excreted. Cadmium may be ingested by inhaling smoke from the burning of industrial metals, but cigarette smoke is also a main source of cadmium inhalation and is the most harmful method of ingestion. Cadmium may also be found in coffee, tea, and crop fertilizers. Neurologic effects of cadmium toxicity include the loss of smell, but a more significant effect is anemia, which can contribute to cerebral hypoperfusion.
Aluminum can be harmful to the neurologic system because it accumulates in the body and can contribute to cognitive impairment and memory loss. Aluminum can be found in food emulsifiers, antiperspirant deodorants, hair spray, baking powder, toothpaste, and drinking water, as well as on cookware surfaces. Moreover, fluoride in drinking water can make aluminum more bioavailable (Russ et al., 2020).