6.1 The Impact of Nutrition on Neurological Wellness Across the Lifespan

Pregnancy

Diet during pregnancy has been shown to have a significant impact on fetal neurodevelopment in a number of ways. Several nutrients and micronutrients have been shown to impact neural tube formation and other aspects of neurological development (Cortés-Albornoz et al., 2021). The developing brain of the fetus consumes more than half of the available nutrition delivered via the placenta, mainly in the form of glucose. The developing fetal brain is vulnerable to insufficient macronutrients and micronutrients, especially in the first stages of pregnancy. Nutrition during pregnancy is of critical importance to both the developing fetus and the mother. This section will discuss the effect of specific nutrients on healthy brain function for both the mother and the developing fetus. Specific vitamins and minerals, such as vitamins A, B₉ (folate), B₁₂ (cobalamin), D, E, and K, as well as certain minerals, such as copper, iron, creatine, choline, zinc, and iodine, are required to prevent a host of neurological conditions in the fetus. They can also impact rates of maternal preeclampsia and postpartum depression.

Table 6.1 outlines the recommended daily allowances for micronutrients for women and men.

Micronutrients

Several requirements for micronutrients increase during pregnancy, especially iron. The development of gray matter in the brain, as well as the structure of dendrites, motor functioning, language ability, and academic performance, are correlated to adequate iron intake (30–40 mg/day). Iron is available in meats (including organ meats such as heart, liver, kidney, and tongue), poultry, fish, and eggs and generally requires maternal supplementation to reach the recommended daily intake (Georgieff, et al., 2020). Choline, another micronutrient (450 mg/day is recommended), plays an important role in cognitive function, especially neural tube development, intelligence, and sensory gating ability. Choline is available in chicken, beef, eggs, and dairy (Steane, et al., 2023). Zinc (11 mg/day recommended) is associated with appropriate movement, normal heart rate variability, and stability of autonomic nervous system. It is available in red meat, shellfish, poultry, pork, and dairy, as well as in fortified cereal, beans, and nuts. Because zinc is essential to carbohydrate and protein metabolism, a deficiency of zinc can be associated with brain degeneration and a decrease in memory and learning, and can lead to a host of neurological disorders (Choi, et al., 2020).

Vitamin A facilitates the patterning of neurons, the development of axons, and the development of the body’s main organs. The pregnant client requires approximately 600 mg/day of vitamin A. Milk and yogurt are rich in vitamin A (Figure 6.2), which is also found in eggs; oily fish; many orange and yellow fruits and vegetables, such sweet potatoes; and leafy green vegetables, such as spinach (Carazo et al., 2021). Given the abundance of vitamin A in the diet, and storage supply of about 4 months in the tissues, supplementation is generally not recommended, because high doses of vitamin A can cause liver toxicity and increase the risk for birth abnormalities.

Figure 6.2 Yogurt is not only rich in vitamin A, but also is a source of calcium, iodine, phosphorus, and riboflavin. (credit: “Yogurt with Blueberries and Granola” by Alabama Extension; ACES | Margaret Barse & Aimee Lewis/Flickr, Public Domain)

Several B vitamins are critical to the normal development of the fetal neural tube. For example, vitamin B₁₂ (cobalamin) and vitamin B₉ (folate) support the development of neurons and myelination of the axons, which carry neurologic messages throughout the body. Folate is integral in fetal brain development, especially during periods of rapid growth and development (Li et al., 2019). Requirements for the B vitamins increase by 50% during pregnancy. For pregnant clients, the requirement is approximately 400 mcg/day of B vitamins.

Vitamin D has a role in regulating gene expression and brain development as well as several other functions, such as the regulation of calcium, the development of dopamine, skeletal regulation, and language development (Larqué, 2018). The maternal requirement of vitamin D during pregnancy is approximately 1500–2000 UL and may be consumed in the diet by eating fatty fish, eggs, beef, and fish liver oil (Chauhan et al., 2023). A deficiency of vitamin D may result in attention deficit hyperactivity disorder and poor language development (Tous, et al., 2020).

Iodine plays an important role in thyroid hormone synthesis and is therefore essential for neurologic development of the fetus. During the first half of pregnancy, a deficiency of thyroid hormone (specifically T4) can disrupt the development of neurons, synapses, and myelin formation. A client with severe iodine deficiency is more likely give birth to a baby with decreased IQ scores or possibly cretinism (altered intellectual disability, small stature, and thickening of the facial features). Supplementing a normal diet with 250 mg/day of iodine is recommended for pregnant clients. Clients contemplating pregnancy may be encouraged to begin iodine supplementation prior to conception. Iodine is available in the diet in most sea fish, especially shellfish, and is fortified in many cereals and grains, in addition to iodized salt. Prenatal supplementation with each of these micronutrients (except vitamin A) is generally recommended. The requirements for each of these are met in daily intake of a prenatal vitamin, so additional supplementation is not recommended.

The phospholipids (fats that contain phosphorus) in the plasma membrane, called gangliosides (lipids that carry sialic acid residues), are essential for fetal brain maturation and can determine normal neural repair and apoptosis, neurotransmitter release, and transmission of signals across cells (Sipione et al., 2023). Severe neurodevelopmental and neurodegenerative problems can result from decreased levels of gangliosides. Clients who carry a rare autosomal recessive gene mutation, such as Tay-Sachs disease (a rare disease that destroys nerve cells in the brain and spinal cord), cannot synthesize gangliosides due to the deficiency of an enzyme (hexosaminidase A). These clients will develop an accumulation of these fatty substances, primarily in the brain and spinal cord. Symptoms include slowed development in the infant, and stiff muscles and seizures may manifest. A similar gene mutation affecting gangliosides can result in spastic paraplegia and intellectual disabilities, due to a deficit of gangliosides in the hippocampus (Okuda, 2019). Egg yolks, meat, and milk are the dietary sources of gangliosides (Okuda, 2019).

While a deficiency of nutrients has been shown to have a negative impact on fetal brain development, a high-fat maternal diet and obesity during pregnancy have been correlated to autism and attention deficit disorder among newborns, behavioral disorders in children, and a propensity for obesity in adulthood (Cortés-Albornoz, et al., 2021). Also, high consumption of sugar during pregnancy, especially fructose, has been associated with altered development of the prefrontal cortex and subsequent autism spectrum disorder (Rivell, et al., 2019). Obesity among pregnant clients has been associated with infants exhibiting altered immunity, higher rates of attention deficit hyperactivity disorder, and autism or intellectual developmental delays than children born to mothers with a normal weight (Sanchez et al., 2018). The nature of the maternal diet has been shown to impact the bacterial colonization in the infant’s gut in the early postpartum period, which can impact subsequent neurodevelopment across the lifespan (Al Rubaye, et al., 2020).

As shown in Applying Clinical Judgment to Promote Nutrition for Neurological Wellness, omega-3 fatty acids are required for healthy brain function. A deficiency of these essential brain-building blocks results in brain inflammation and possibly brain injury and stroke. Approximately 1 in every 3,500 full-term infants in the United States will develop an ischemic stroke when expecting mothers do not consume adequate amounts, especially in the first trimester of pregnancy (Dunbar & Kirton, 2018).

Prenatal alcohol intake in any amount has been shown to have a detrimental effect on congenital cognitive impairment, including fetal alcohol spectrum disorder and, if severe, fetal alcohol syndrome (Oei, 2020). Maternal caffeine intake crosses over to the placenta and is associated with altered sleep and movement as well as the ability to learn, because the developing fetus does not possess the enzymes to metabolize caffeine. Maternal caffeine intake of more than 200 mg/day has been associated with shorter stature in early childhood (Gleason et al., 2022).

Impact on the Client’s Health During Pregnancy

The impact of pregnancy on the neurological health of the client is of great concern. Pregnant people’s rates of morbidity and mortality have risen dramatically in recent years, especially in non-Hispanic Black and Hispanic individuals (Hoyert, 2023). Hormones change during pregnancy, and particularly the rise in progesterone can affect maternal health. Current nutritional recommendations for neurologic health during pregnancy include a diet rich in fresh fruits and vegetables, whole-grain cereals, milk, and dairy products, as well as meat, fish, and eggs as they are rich in vitamins A, C, and D as well as calcium and phosphorus.

During the antepartum period, many people have an increased interest in eating carbohydrates, and if toothbrushing does not occur as often, dental caries and plaque are more likely. Dental infections and caries have long been associated with the development of a stroke, but dental inflammation has also been associated with premature contractions, placing the fetus at risk for premature birth, low birth weight babies (Alrumayh et al., 2021). While regular oral care during pregnancy (toothbrushing and flossing at least twice a day) require diligence during pregnancy, dental procedures such as extractions and root canals, if required, are performed with caution during pregnancy, and may be delayed until after the first trimester.

Sugars, dried fruits, and chewy candy should be avoided to promote optimal dental health, as this can also impact the neurologic health of the pregnant client. Gingivitis and tooth decay are more likely during pregnancy, and this is thought to be associated with hormonal changes, especially estrogen and progesterone. Those who develop morning sickness with vomiting during pregnancy are more likely to have gingivitis, which can lead to an acidic environment in the mouth and, consequently, tenderness and minor bleeding can occur, making toothbrushing uncomfortable.

High levels of fat in the maternal diet and an inactive lifestyle are associated with high cholesterol and high blood pressure. A significant portion of people who consume a high-fat diet and are inactive during pregnancy develop preeclampsia, placing them at a five-times higher-than-average risk for stroke, not only in the peripartum period, but also in later life (de Havenon et al., 2021). Pregnant clients who develop frequent migraine headaches are more likely to develop preeclampsia during pregnancy (Zambrano & Miller, 2019). Clients who develop an infection such as a urinary tract infection or sepsis during their pregnancy are more likely to be readmitted to the hospital for a stroke after the delivery (Zambrano & Miller, 2019). Approximately 7.4% of maternal deaths are a result of stroke. Stroke is now the second-leading cause of maternal death in Japan among women older than 40 years, and many of these are considered preventable (Zambrano & Miller, 2019). A large percentage of maternal deaths in the United States are associated with inadequate prenatal care and preeclampsia (Elgendy et al., 2021). In addition to preeclampsia and stroke during pregnancy, Bell’s palsy can develop during delivery, and a temporary paralysis of one side of the face can last up to 6 months postpartum.

Infancy

The development of the brain and nervous system is the most rapid in the first two years of life. Given the known benefits of breastfeeding over infant formula, nutritional support with human breast milk is critical to neurological development during infancy. Specifically, the development of visual function and other cognitive domains are improved when babies are breastfed throughout infancy (Nieto-Ruiz, 2019). A deficiency of a host of macronutrients and micronutrients, such as protein, carbohydrates, certain fats, iron, zinc, copper, iodine, selenium, vitamin A, choline, folate, and vitamin B₁₂ (cobalamin), have been shown to be essential in preventing certain neurologic disorders, such as anorexia, irritability, growth retardation, and developmental regression (Nawaz, et al., 2020). Iron deficiency alters myelin formation in infancy as well as the development of the hippocampus (brain structure responsible for emotion, memory, and autonomic nervous system) and neurotransmitters. The impact of maternal iron deficiency includes a reduction in memory, motor, and behavioral affect in the infant. A zinc deficiency interferes with both hippocampal and cerebellar development. Polyunsaturated fatty acids also affect membrane function and the development of appropriate synapses.

Childhood

The brain reaches 80% of its adult weight by age 3 (Bethlehem et al., 2022) and is exceptionally sensitive to any nutritional deficiencies. Glucose metabolism in the brain continues to accelerate from birth to 4 years. At age 4 years, glucose metabolism occurs at approximately twice the rate as that of an adult. This accelerated metabolic rate continues until age 9 or 10 years and then begins to slow to the adult level during late adolescence. Because the brain cannot store glucose, a continuous supply of glucose by eating frequent meals is paramount. The effect of overnight fasting can have an adverse effect on children; therefore, breakfast is an extremely important meal to nourish the brain and improve cognitive function.

A breakfast that is rich in low glycemic carbohydrates is known to result in optimal cognitive performance. Different types of breakfast may impact the development and performance of various gray and white matter in the brain (Arora, 2022). The effect of long-chain polyunsaturated fatty acids (LCPUFA) is essential for brain function, especially in the brain’s gray matter. Given the rapid brain development, especially in early childhood, it is critical to ensure adequate micronutrients intake, which can be challenging. Deficiencies of micronutrients such as iron, folate, and vitamin B₁₂ may become evident around age 5–6 years, as deficiencies are associated with poor cognitive performance, especially in the school setting (Arora, 2022).

Micronutrient deficiency may be more apparent among children whose mothers had experienced inflammatory bowel diseases, celiac disease, or ulcerative colitis, as these vitamins are poorly absorbed in the intestines in these conditions. For children who are deficient, dietary supplementation with micronutrients can improve cognitive performance, especially if the breakfast is low in sugar (Arora, 2022).

The prevalence of pediatric obesity climbed to 19.7% between 2017 and 2020 in the U.S. (CDC, 2023b). Some studies suggest that there is a biological link between childhood obesity and lower cognitive function and that this effect is related to insulin resistance. However, these studies are inconclusive, especially when sociodemographic factors are considered. For healthy children, the Mediterranean diet is an example of a diet that can provide the essential nutrients required for the development of a healthy neurologic system.

Adolescence

Multiple studies of the diets of adolescents have shown that there is a direct relationship between diet and brain development (Arora, 2022). Diet is associated with various aspects of mood, anxiety, depression, and other mental health disorders. A disproportionate percentage of teens are known to have an eating disorder (i.e., anorexia nervosa or bulimia), and this has a direct result on neurotransmission within the brain (Aurora, 2022). A poor diet during adolescence can result in structural changes in the brain, causing poor cognitive function, mood changes, and emotional imbalances. These structural changes may become permanent, as the brain is still developing in adolescence, and the processes of neurotransmission in the brain is still evolving during this period. For example, dopamine is a neurotransmitter in the brain that is responsible for pleasure and reward responses, and if the brain interprets a message that a cheeseburger or ice cream is a reward, dopamine is released. This dopamine effect is much more pronounced in an adolescent brain than in an adult, because adolescents have more dopamine receptors than adults. When the adolescent brain is rewarded with poor diet choices, this impact carries over into adulthood.

Healthy food choices, including a moderate intake of low-fat dairy and meats with low levels of refined sugars, promote the development of healthy bacteria, acting as natural probiotics. Bacteria in the stomach influence the production of serotonin and create a lining of the stomach that protects against harmful bacteria, limiting inflammation and improving the absorption of nutrients. Serotonin is produced in the intestine and regulates sleep, appetite, mood, and pain inhibition. The creation of healthy bacteria in the gut is critical, because bacteria activate the pathway between the brain and GI tract.

A poor diet during adolescence creates a disruption in healthy gut bacteria, resulting in an inability to absorb nutrients or produce serotonin. The neurologic impact of a poor diet during adolescence is a reduced attention span, an inability to learn or remember new information, and an inability to regulate one’s mood. The typical teenage diet in the U.S. often includes sugary drinks, processed sugars, fried foods, and an imbalance in healthy nutrients. A poor diet in adolescence also contributes to the development of depression, sleep disturbances and mood disorders. It can also contribute to an early development of heart disease, type 2 diabetes, memory disturbances, and brain inflammation (Griebsch et al., 2023; Moscatelli et al., 2023). Some teens have tried to reduce processed sugar intake by switching to sports drinks containing aspartame. However, aspartame contains phenylalanine, which increases brain inflammation and can worsen brain function, increasing the risk for developing Alzheimer’s disease and other forms of neurodegeneration (Czarnecka et al., 2021). Conversely, many children and adolescents have moved toward a health-conscious lifestyle that includes vegetarian or vegan diets (Figure 6.3). Although nutritional needs can generally be met with a plant-based diet, the nutrient requirements of adolescents are higher per kilogram of body weight than adults, and this consideration is important in diet planning. Nutritional deficiencies, especially of omega-3 fatty acids, iron, zinc, and B₁₂, are more common among vegetarians and vegans, requiring close monitoring by health care professionals (Rudloff et al., 2019).

Adulthood

The needs of adults change as aging occurs. While adulthood begins at 18 years, the needs of adults change as a person enters their 30s, 40s, 50s and 60s due to changes in metabolic rate, activity levels, the physical demands by occupation, hormonal changes, and a wide range of other factors. Moreover, nutritional needs may vary based on a person's sex. For example, health and nutrition for females must consider important factors across the lifespan, such as pregnancy, breastfeeding, and menopause. As females age, they are at a higher risk than males of cardiac disease, breast cancer, and osteoporosis.

Specific recommendations for macronutrients to maintain neurologic health can also vary depending on a range of factors, including a person's sex, environment, and other characteristics or circumstances. The degree of physical activity alters protein requirements. Physical body size and weight alter caloric needs. Carbohydrates provide the main source of energy. In general, 130 g/day of carbohydrates are recommended, and these should be consumed from high-fiber whole grains, fruits, vegetables, and legumes, as well as low-fat yogurt and other dairy products. A dietary intake of polyunsaturated fats, which can be found in vegetable oils, nuts, seeds, and fish oil, should comprise around 15% of the adult diet.

While caloric needs are higher in early adulthood, this need often declines as a person ages. Because many adults do not adjust their diet as they age, overconsumption of calories coupled with a decline in physical activity often results in adult-onset obesity, which can be associated with poor cognitive status. Some estimates report that 42.5% of adults in the U.S. are overweight or obese, and it varies by race and ethnicity (Fryar, et al. 2021). Due to the inadequacies of the traditional Western diet, many adults are also nutrient deficient, especially in micronutrients, even if their caloric intake exceeds the body’s needs.

Older Adults

The changing nutritional requirements in older adults are more relevant than ever before. In 2019, estimates show that there were more than 703 million people globally over age 65, and more than 50 million were diagnosed with dementia. By the year 2050, it is projected that 1.5 billion people will be over age 60, and 153 million will be living with dementia (Alzheimer’s Disease International, 2023). Nutritional strategies, including the intake of specific macronutrients and micronutrients, such as those rich in B vitamins, long-chain polyunsaturated fatty acids, and flavonoids (foods that have antioxidant properties due to their variable phenolic composition, like fruits and vegetables, tea, wine, and whole grains), have been shown to delay or slow the onset of age-related conditions. Supplementing the diet with micronutrients has been shown to improve cognition in some studies of clients with Alzheimer’s disease, but the best health benefits have been verified with a varied multinutrient-rich diet rather than supplements alone (Fei et al., 2022).

The process of aging is associated with a loss of muscle mass. While a variety of food sources are recommended to support brain health, those containing foods rich in iron, folate, calcium, and vitamins A, C, and D, are particularly important for supporting muscle mass as well. Adequate intake of vitamin B₁₂ among older adults is recommended to maintain the integrity of nerve cells. Foods high in vitamin B₁₂ include eggs, fortified breakfast cereal, and certain fish, such as tuna. However, the absorption of some vitamins may be reduced due to both age-related and other changes in the gut, as well as the effect of medications like metformin, proton pump inhibitors, vitamin C supplements, colchicine, and medications that are used to treat peptic ulcers and other gastrointestinal problems. The tendency of older adults to become dehydrated can also affect the ability to absorb nutrients, and an increase in water intake as well as fresh fruits and vegetables can help to overcome dehydration. Special nutritional considerations for older adults should include an understanding of maintaining adequate nutrient and fluid intake, the client’s sensitivities to certain foods, and any challenges with chewing or swallowing.