diagram of a neuronSummary

Many nutrients have well-established roles in the formation and development of the brain and continue to support brain activity and brain health throughout life. Severe deficiency of certain micronutrients (the B-vitamins in particular) can result in neurologic abnormalities and symptoms. Although higher dietary intake of certain nutrients (especially long-chain omega-3 fatty acids) and dietary factors (especially flavonoids) is associated with beneficial effects on cognitive function, it is unknown if micronutrient supplementation beyond the recommended dietary allowance (RDA) will benefit cognitive function in healthy individuals. There is some evidence that correcting a micronutrient deficiency (vitamin C, vitamin E, vitamin D) or supplementation in those with mild cognitive impairment (long-chain omega-3 fatty acids, folic acid, vitamin B6, vitamin B12) can have a positive effect on some measures of cognitive function.

Overview

The Brain

Every single thing we do, think, and say is controlled by the brain. It’s hard to imagine, but all of our actions are the result of the transmission of electrical and chemical signals between neurons. The human brain contains an estimated 100 million neurons, each with thousands of connections. For each neuron, there are an estimated five to ten glial cells, which interact with neurons and influence their activity. A neuron typically consists of four main parts: (1) a cell body, (2) dendrites, (3) an axon, and (4) axon (synaptic) terminals. The synapse is the microscopic region between an axon terminal of one neuron and neurotransmitter receptors on a second cell; the second cell may be a part of another neuron, a muscle cell, or a gland cell.

A network of blood vessels permeates the brain and associates with the millions of neurons and glial cells to provide oxygen, nutrients, and other vital substances, and to remove waste. The cells that line the blood vessels of the brain form a specialized barrier, the blood-brain barrier (BBB), that facilitates the transfer of certain substances while impeding the entry of others.

The brain may seem an inert lump, but it uses the most energy of all the organs in our body. Twenty to twenty-five percent of our basal metabolic rate (the amount of energy used by our bodies at rest) is used to fuel the brain. This energy is essential to maintain both fundamental and complex brain functions. Fundamental functions include things like neurotransmitter synthesis, nerve impulse transmission, and nutrient transport. Complex functions include things like behavior and higher-order brain activities (cognitive functions), such as attention, memory, and language.

The brain requires a constant supply of glucose. Blood glucose concentration is maintained in a tight range at all times in order to keep glucose supply to the brain constant. Between meals, the liver releases glucose from short-term storage (glycogen) and makes glucose from amino acids for use by the brain. In extreme circumstances when glucose supplies fall (such as during prolonged starvation), the brain can use an additional fuel source: ketone bodies. Ketone bodies, also made by the liver, are the byproducts of the breakdown of stored fat.

B-vitamin deficiency impairs glucose and energy metabolism in brain cells, which can contribute to malfunction and damage. B-vitamins are also required for the synthesis of several neurotransmitters. See Table 1 for neurologic symptoms associated with severe B-vitamin deficiency.

Cognitive Function

Cognition basically means using your brain. It is a very broad term that includes many varied and complex brain activities (or cognitive functions), such as attention, memory, processing speed, and executive functions (i.e., reasoning, planning, problem solving, and multitasking).

In the study of cognitive function related to healthy aging, three main categories are described:

(1) Normal cognitive aging - As we get older, the brain shrinks, the number of synapses decreases, and the number of receptors for multiple different neurotransmitters decreases. All of these age-related changes can contribute to minor cognitive deficits, especially in memory, processing speed, cognitive flexibility, attention, and executive functions. The rate of brain aging varies dramatically from person to person. The good news is that the aged brain is capable of change, and there are things you can do to slow down age-related cognitive decline (see HIGHLIGHT: PHYSICAL ACTIVITY).

(2) Mild cognitive impairment - There is no precise definition on the diagnostic criteria for mild cognitive impairment (MCI). MCI refers to some mild but noticeable impairment in cognitive function that does not affect instrumental activities of daily living (for example, becoming disoriented in familiar places or forgetting recent conversations). Generally, individuals with MCI have an increased risk of developing dementia.

(3) Dementia - Dementia is a loss of cognitive and behavioral abilities to an extent that is severe enough to interfere with daily life. There are different types of dementia:

  • The most common form of dementia in older individuals (65 years and older) is caused by Alzheimer’s disease, a disease in which abnormal protein plaques and tangles accumulate in the brain (see Alzheimer’s disease). Alzheimer’s dementia accounts for up to 70% of dementia cases in the US.
  • Vascular dementia is the second most common dementia in the elderly. It results from blockage or leakage of arteries in the brain due to cardiovascular disease (see Stroke).

There are major challenges in studying the effect of nutrients on cognitive function, making the scientific evidence difficult to compare. Several methodological issues contribute to mixed results — for example, tests used to assess cognitive function vary greatly, study participants are not always equivalent, study duration may be too short to see an effect, or the dose, form, and combinations of the nutrients of interest may differ across studies. Nonetheless, some nutrients have well-established roles in brain health and scientists are investigating their possible importance in improving cognitive function and preventing cognitive decline. See below for specific information about nutrients and dietary factors relevant to cognitive function.

HIGHLIGHT: PHYSICAL ACTIVITY
  • Physical activity increases neuronal cell number and survival and increases the volume of the hippocampus, a region of the brain that is important for forming new memories.
  • Even the aged brain is capable of these improvements. Stay physically active to help maintain cognitive function at any age.
DEFINITIONS
Cognition - the process of thinking
Cognitive functions - the complex brain activities involved in acquiring information and knowledge
Neuron - a type of nerve cell that receives and transmits information within the brain and between the brain and the rest of the body
Glial cell - the most abundant cell type in the nervous system; glial cells provide support and regulatory functions for neurons
Neurotransmitter - a chemical compound used by neurons to signal to each other
Synapse - sites of communication between neurons
Myelin sheath - the insulating layer of tissue made up of lipids and proteins that surrounds the axons of neurons; when damaged or absent, the conduction of nerve signals is slowed, causing numerous neurologic problems
Plasticity - the ability to change
Table 1. Severe B-vitamin Deficiency Causes Neurologic Symptoms 
Micronutrient Recommended Dietary Allowance (RDA) Neurologic Symptoms of Severe Deficiency 
Thiamin (vitamin B1)

Men: 1.2 mg/day

Women: 1.1 mg/day

Damage to peripheral nerves resulting in muscle weakness, cramps, increased sensitivity, and deep pain
Riboflavin (vitamin B2)

Men: 1.3 mg/day

Women: 1.1 mg/day 

No specific neurologic symptoms, though muscle weakness and fatigue observed 
Niacin (vitamin B3)

Men: 16 mg/day

Women: 14 mg/day 

Headache, fatigue, apathy, depression, ataxia, poor concentration, delusions, hallucinations, and dementia 
Pantothenic acid (vitamin B5) 5 mg/day  Peripheral nerve damage, numbness and tingling of hands and feet, headache, fatigue, and insomnia 
Vitamin B6

Men: 1.3 mg/day (19-50y); 1.7 mg/day (51y and older)

Women: 1.3 mg/day (19-50y); 1.5 mg/day (51y and older) 

Irritability, depression, confusion, and convulsions 
Biotin (vitamin B7) 30 µg/day Depression, lethargy, hallucinations, and numbness and tingling of the extremeties 
Folate (vitamin B9) 400 µg/day Neural tube defects in the developing embryo 
Vitamin B12 2.4 µg/day Tingling and numbness of the extremeties, nerve damage, memory loss, disorientation, and dementia

Abbreviations: mg, milligrams; µg, micrograms; y, years

For references and more information, see the in-depth article on Cognitive Function

References

Nutrition Research

DEFINITIONS
Test tube (in vitro) experiment - a research experiment performed in a test tube, culture dish, or other artificial environment outside of a living organism; in vitro is a Latin phrase meaning in glass
Animal experiment - a research experiment performed in a laboratory animal; many different animal species are studied in the laboratory, including terrestrial (land), aquatic (water), and microscopic animals
Observational study - a human research study in which no experimental intervention or treatment is applied, and participants are simply observed over time
Randomized controlled trial - a human research study in which participants are assigned by chance alone to receive either an experimental agent (the treatment group) or a placebo (the control group)
Placebo - a chemically inactive substance

Long-chain Omega-3 Fatty Acids

What they do

General

  • Essential fatty acids are a type of polyunsaturated fatty acid (PUFA) that cannot be made in the body and must come from the diet.
  • Essential fatty acids are structural components of every cell in the body and are converted to compounds that influence inflammation and immunity.
  • There are two classes of essential fatty acids: omega-6 PUFAs and omega-3 PUFAs.

Cognition-specific

  • Nerve cell membranes are very rich in fatty acids, especially the long-chain omega-3 PUFA, docosahexaenoic acid (DHA).
  • DHA influences nerve cell function through its direct maintenance of cell membrane fluidity and integrity and through the generation of compounds with neuroprotective activities.
  • Fish oil, a good source of the long-chain omega-3 PUFAs eicosapentaenoic acid (EPA) and DHA, may reduce vascular risk factors associated with cognitive decline, thus providing benefits to both cardiovascular and brain health.
What we know
  • Overall, observational studies report that higher levels of fish intake or higher concentrations of omega-3 PUFA in the blood are associated with better cognitive performance and lower risks of cognitive decline and some types of dementia.
  • In healthy individuals, omega-3 PUFA supplements have not been shown to improve cognitive function in children, adults, or the elderly.
  • In individuals with mild cognitive impairment, omega-3 PUFA supplements may have beneficial effects on specific cognitive functions, such as immediate recall and processing speed.

For references and more information, see the section on Age-related cognitive decline in the in-depth article on Cognitive Function.

There are two essential fatty acids: linoleic acid (an omega-6 polyunsaturated fatty acid) and alpha-linolenic acid (an omega-3 polyunsaturated fatty acid). These fatty acids are considered essential nutrients because they cannot be made in the body and must be consumed in the diet. Vegetable oils, especially safflower oil, sunflower oil, and corn oil, are a good source of linoleic acid.Flax and chia sees, walnuts, canola oil, and soybean oil are good sources of alpha-linoleic acid. Inside body tissues, the essential fatty acids are converted to long-chain fatty acids. Due to low efficiency of conversion, it is recommended to obtain eicosapentaenoic acid (EPA) and docosapentaenoic acid (DHA) from additional sources. Oily fish, fish oil supplements, krill oil supplements, and algae oil supplements are good sources of EPA and DHA.

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Choline

What it does

General

  • Choline is an essential constituent of cell membranes, influences the production of several important neurotransmitters, and helps transport and metabolize fatty acids and cholesterol.
  • Additionally, choline helps convert homocysteine to methionine, an amino acid used in countless essential cellular activities.
  • Choline can be made by the body in small amounts, but not enough to support health. Therefore, choline must also be obtained from dietary sources and is considered an essential nutrient.

Cognition-specific

  • Choline is needed for myelination of neuron axons and is a precursor for acetylcholine, an important neurotransmitter involved in muscular movement and memory.
What we know
  • Only two observational studies have investigated the association between dietary intake or blood concentration of choline and cognitive function in adults. In both cases, higher intake or higher blood concentrations were associated with better performance on specific cognitive functions.
  • However, randomized controlled trials have found no clear beneficial effects of choline supplementation on cognitive function in healthy populations.

For references and more information, see the section on Cognitive function in older adults in the Choline article.

Choline Flashcard. Main functions: 1) structural component of all cell membranes, 2) transport and metabolism of fat and cholesterol, 3) helps make some important neurotransmitters, and 4) helps maintain normal levels of homocysteine in the blood. Good sources: egg (1 large), 147 mg; meat (beef and poultry), beef (3 ounces), 97 mg; seafood (fish and shellfish), scallop (steamed, 3 ounces) 94 mg (mg=milligrams; a three-ounce serving of meat or fish is about the size of a deck of cards; Daily Recommnedation: 550 mg for all men and 425 mg for all women; Special Notes: 1) Choline can be made in the body, but it is not enough to support health. Therefore, it must also be consumed in the diet. 2) A varied diet should provide enough choline for most people, but strict vegetarians who don't consume milk or eggs may be at risk of inadequate choline intake.

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Folate (Folic acid)

What it does

General

  • Folate is a B-vitamin required for DNA synthesis and the formation of new cells.
  • Additionally, the B-vitamins folate, vitamin B12, and vitamin B6 work together to convert homocysteine to methionine, an amino acid used in countless essential cellular activities.

Cognition-specific

  • Folate deficiency may lead to decreased synthesis of methionine and the accumulation of homocysteine.
  • Methionine is used in methylation reactions, which are essential for the maintenance of the myelin sheath of nerve cells and for the synthesis of neurotransmitters.
  • Too much homocysteine in the blood has been associated with an increased risk of cognitive decline and dementia in older adults.
What we know
  • Although supplementation with folic acid, vitamin B12, and vitamin B6 successfully lowers homocysteine concentration in the blood, no significant effect on cognitive function or on the prevention of cognitive deterioration has been demonstrated in cognitively healthy older adults.
  • It is unclear if B-vitamins can prevent cognitive decline in individuals with mild cognitive impairment. Screening for high homocysteine in individuals with early signs of age-related cognitive impairment may be warranted because B-vitamin supplementation might slow the rate of brain atrophy in this population.

For references and more information, see the section on Alzheimer’s disease and cognitive impairment in the Folate article.

Folate Flashcard. Main Functions: 1) required for DNA synthesis, 2) supports cell growth and repair, 3) helps prevent neural tube defects. Good Sources: legumes (beans, peas, lentils), lentils (cooked) one-half cup = 179 micrograms dietary folate equivalents (DFE); green leafy vegetables (kale, spinach), spinach (cooked) one-half cup, 131 micrograms DFE; fortified food and supplements, sliced bread (enriched), 1 slice, 84 micrograms DFE. Daily Recommendation: 400 micrograms DFE for adults, 600 micrograms DFE for pregnant women. Special Notes: 1) Folate is a general term that refers to both natural folates in food and folic acid, the synthetic form used in supplements and fortified food. 2) DFE = a unit of measure that accounts for differences in the absorption of naturally occurring food folate and synthetic folic acid. 3) To reduce the risk of neural tube defects, all women capable of becoming pregnant should consume 400 micrograms of folic acid daily in addition to the folate obtained from a varied diet. 4) Very high-dose folic acid supplementation (5,000 micrograms) can mask a vitamin B12 deficiency, specifically signs of nerve damage.

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Vitamin B6

What it does

General

  • Vitamin B6 helps convert food into usable energy and assists in the formation of neurotransmitters, red blood cells, proteins, and DNA.
  • Additionally, the B-vitamins folate, vitamin B12, and vitamin B6 work together to convert homocysteine to methionine, an amino acid used in countless essential cellular activities.

Cognition-specific

  • A form of vitamin B6, pyridoxal 5’-phosphate (PLP), is a required cofactor for the synthesis of several neurotransmitters, including GABA, dopamine, norepinephrine, and serotonin.
  • Too much homocysteine in the blood has been associated with an increased risk of cognitive decline and dementia in older adults.
What we know
  • Symptoms of vitamin B6 deficiency include abnormal electrical activity in the brain, irritability, depression, and confusion.
  • Although supplementation with folic acid, vitamin B12, and vitamin B6 successfully lowers homocysteine concentration in the blood, it has not been shown to improve cognitive function in cognitively healthy older adults.
  • It is unclear if B-vitamins can prevent cognitive decline in individuals with mild cognitive impairment. Screening for high homocysteine in individuals with early signs of age-related cognitive impairment may be warranted because B-vitamin supplementation may slow the rate of brain atrophy in this population.
HIGHLIGHT
Long-term supplementation with very high doses of vitamin B6 (500 to 1,000 mg/day) may result in painful neurological symptoms known as sensory neuropathy (damage to the sensory nerves). Symptoms include pain, numbness, and tingling of the extremities and in severe cases, difficulty walking. To prevent sensory neuropathy in virtually all individuals, the Food and Nutrition Board of the Institute of Medicine set the tolerable upper intake level (UL) for vitamin B6 (aka pyridoxine) at 100 mg/day for adults.

For references and more information, see the section on Age-related cognitive decline in the in-depth article on Cognitive Function.

Vitamin B6 Flashcard. Main Functions: 1) helps convert food into energy, 2) helps make red blood cells, 3) helps maintain normal levels of homocysteine in the blood. Good Sources: Fish (slamon, tuna, halibut), wild salmon, 3 ounces, 0.5-0.8 mg; poultry (turkey, chicken, duck), light-meat turkey (cooked), 3 ounces = 0.7 mg; nuts (hazelnuts, walnuts) pistachio nuts, 1 ounce or 47 pistachios = 0.5 mg. Daily Recommendation: 2 mg for all adults. Special Notes: 1) The Daily Recommendation listed is specific to the LPI based on extensive review of the scientific evidence. The Institute of Medicine's Recommended Dietary Allowance (RDA) is 1.3 mg/day for adults 19-50 years, 1.7 mg/day for men 51 years and older, and 1.5 mg/day for women 51 years and older. 2) In the US, vitamin B6 is added back to refined grains. Therefore, enriched products are also a source of vitamin B6. 3) Excessive supplementation of vitamin B6 (more than 100 mg/day) can cause nerve damage and skin lesions.

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Vitamin B12

What it does

General

  • Vitamin B12 helps convert food into usable energy, is required for proper nerve function, and assists in the formation of red blood cells, proteins, and DNA.
  • Additionally, the B-vitamins folate, vitamin B12, and vitamin B6 work together to convert homocysteine to methionine, an amino acid used in countless essential cellular activities.

Cognition-specific

  • Vitamin B12 deficiency, like folate deficiency, may lead to decreased synthesis of methionine and the accumulation of homocysteine.
  • Methionine is used in methylation reactions, which are essential for the maintenance of the myelin sheath of nerve cells and for the synthesis of neurotransmitters.
  • Too much homocysteine in the blood has been associated with an increased risk of cognitive decline and dementia in older adults.
What we know
  • Vitamin B12 deficiency, which affects 10 to 15% of adults over the age of 60, is frequently associated with neurological problems. Such neurological symptoms include numbness and tingling of the extremities (especially the legs), difficulty walking, concentration problems, memory loss, disorientation, and dementia.
  • Although supplementation with folic acid, vitamin B12, and vitamin B6 successfully lowers homocysteine concentration in the blood, no significant effect on cognitive function or on the prevention of cognitive deterioration has been demonstrated in cognitively healthy older adults.
  • It is unclear if B-vitamins can prevent cognitive decline in individuals with mild cognitive impairment. Screening for high homocysteine in individuals with early signs of age-related cognitive impairment may be warranted because B-vitamin supplementation may slow the rate of brain atrophy in this population.
HIGHLIGHT
  • The recommended dietary allowance (RDA) for vitamin B12 is 2.4 micrograms/day for all adults; older adults (>50 years) should meet the RDA by consuming fortified food or supplements.
  • Two things are needed to absorb vitamin B12 from food sources:
    • an acidic stomach environment that frees vitamin B12 from the food matrix
    • a special protein called intrinsic factor that allows vitamin B12 to be absorbed by cells in the small intestine
  • Poor absorption of vitamin B12 from food sources is common among older adults and long-term consumers of drugs that reduce stomach acid production.
  • The LPI recommends that adults over the age of 50 take 100 to 400 micrograms of supplemental vitamin B12 daily.

For references and more information, see the section on Age-related cognitive decline in the in-depth article on Cognitive Function.

Vitamin B12 (cobalamin) Flashcard. Main Functions: 1) Helps make red blood cells, 2) Required for proper nerve function, and 3) Helps maintain normal levels of homocysteine in the blood. Good Sources: Vitamin B12 is only found in animal products. Seafood (shellfish, fish), clams (steamed) 3 ounces = 84 micrograms; poultry (turkey, chicken, duck), roasted turkey, 3 ounces = 0.8 micrograms; red meat (beef, pork, lamb), lean beef plate steak (grilled), 3 ounces = 6.9 micrograms. Daily Recommendation: adults 19-50 years = 2.4 micrograms; LPI recommends older adults (51 years and older) take 100-400 micrograms of supplemental vitamin B12. Special Notes: 1) Over-the-counter antacids reduce vitamin B12 absorption. 2) The capacity to absorb vitamin B12 from food goes down with age. 3) Symptoms of vitamin B12 deficiency include tingling and numbness in the extremities, nerve damage, and memory loss. 4) Older adults and individuals consuming a vegan diet should obtain vitamin B12 from supplements or fortified food.

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Vitamin C

What it does

General

  • Vitamin C (ascorbic acid) is a water-soluble vitamin that neutralizes a variety of reactive oxygen species (ROS), recycles important cellular antioxidants, augments the functional activity of immune cells, and helps make collagen, L-carnitine, and several neurotransmitters.

Cognition-specific

  • Vitamin C accumulates in the central nervous system, with neurons of the brain retaining especially high concentrations.
  • Vitamin C is a required cofactor for an enzymatic reaction that produces the neurotransmitter norepinephrine from dopamine.
  • Brain cells are rich in long-chain polyunsaturated fatty acids (which are prone to oxidative damage) and have high rates of metabolic activity (and thus increased formation of ROS, natural byproducts of cellular metabolism). Antioxidant nutrients like vitamin C and vitamin E thus serve important protective functions in the brain.
What we know
  • Some observational studies have found that higher intakes of vitamin C and vitamin E are associated with a slower rate of cognitive decline in older adults (aged 60 and above). However, the majority of observational studies report no association.
  • Randomized controlled trials have not demonstrated a beneficial effect of antioxidant supplements (vitamin C, vitamin E, and β-carotene) on cognitive function in healthy older adults.
  • Overall, the evidence suggests that avoiding vitamin C deficiency and consuming a healthy diet can have a protective effect against age-related cognitive decline.
DEFINITIONS
Reactive oxygen species (ROS) - highly unstable oxygen-containing compounds that react easily with nearby cellular structures, potentially causing damage.
Oxidative damage - damage that arises when the production of reactive oxygen species exceeds the ability of an organism to eliminate or neutralize them.
Antioxidants - compounds that prevent or repair the damage caused by reactive oxygen species.
HIGHLIGHT
  • The recommended dietary allowance (RDA) for vitamin C is 75 mg/day for adult women and 90 mg/day for adult men.
  • The Linus Pauling Institute recommends a vitamin C intake of at least 400 mg daily for adult men and women. This level of intake results in near-maximal concentrations of vitamin C in the blood and circulating cells and is associated with several beneficial health effects.
  • If you supplement with vitamin C, two separate 250-mg doses taken in the morning and evening is recommended.

For references and more information, see the section on Age-related cognitive decline in the in-depth article on Cognitive Function.

Vitamin C (ascorbic acid) Flashcard. Main Functions: 1) Antioxidant defense, 2) Enhances immune function, 3) Needed to make collagen, carnitine, and the neurotransmitters serotonin and norepinephrine. Good Sources: Fruit, 1 medium-sized kiwifruit = 90 mg; strawberries, 1 cup whole, 85 mg; Vegetables (broccoli, kale, tomatoes), sweet red pepper (one-half cup, chopped) = 95 mg. Daily Recommendation is 400 mg for all adults. Special Notes: 1) Heat destroys vitamin C. Try to eat fresh foods and cook by steaming, microwaving, or stir-frying. 2) Vitamin C in food is identical to vitamin C in supplements. 3) The Daily Recommendation listed is specific to the LPI based on extensive review of the scientific evidence. The Institute of Medicine's Recommended Dietary Allowance (RDA) is 90 mg/day for men and 75 mg/day for women.

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Vitamin D

What it does

General

  • Vitamin D is a fat-soluble vitamin that helps maintain calcium and phosphorus balance, promotes bone health, regulates immune function, and influences cell growth and development.

Cognition-specific

  • The vitamin D receptor, which mediates most actions of vitamin D, is present in neuronal and glial cells in almost all regions of the brain and spinal cord.
  • The active form of vitamin D influences many activities in the CNS:
    • the growth, development, and survival of neurons
    • the genetic expression of several neurotransmitters, including acetylcholine, dopamine, serotonin, and gamma-aminobutyric acid (GABA).
What we know
  • Low vitamin D status (serum 25-hydoxyvitamin D below 30 ng/mL [75 nmol/L]) is extremely common worldwide. Estimates range from 52 to 77% of sampled populations having low vitamin D status.
  • Low vitamin D status increases the risk of cognitive decline and dementia in older adults.
  • It is not yet known if vitamin D supplementation can prevent cognitive decline in people with low vitamin D status since randomized controlled trials are lacking.
  • Nonetheless, vitamin D supplementation with the objective of raising 25-hydroxyvitamin D concentration above 30 ng/mL is recommended in the care of older adults with cognitive disorders.
HIGHLIGHT
  • The recommended dietary allowance (RDA) for vitamin D is 600 IU (15 µg)/day for adults aged 19 to 70 years and 800 IU (20 µg)/day for adults aged 71 years and older.
  • Vitamin D is notoriously difficult to obtain from food sources alone and national surveys indicate that 94% of the US population is not meeting the dietary requirement for vitamin D.
  • The LPI recommends that generally healthy adults take 2,000 IU (50 micrograms) of supplemental vitamin D daily.

For references and more information, see the section on Vitamin D in the in-depth article on Cognitive Function.

Vitamin D (calciferol) Flashcard. Main Functions: 1) Facilitates absorption of calcium and phosphorus, 2) Promotes bone health, 3) Required for proper immune function, and 4) Influences cell growth and development. Good Sources: Fatty Fish (salmon, mackerel, sardines), pink canned salmon, 3 ounces = 465 IU or 11.6 micrograms; Canned mackerel, 3 ounces = 211 IU for 5.3 micrograms; Fortified food, low-fat milk, vitamin D fortified, 8 ounces = 98 IU or 2.5 micrograms. Daily Recommendation: 600-1,000 IU (15-25 micrograms) for chldren and adolesents (4-18 years), because vitamin D is scarcely found in food, it may be necessary to take supplements. 2,000 IU or 50 micrograms for all adults, this amount applies to supplemental vitamin D, which is recommended in addition to vitamin D from a mixed diet. Special Notes: 1) The Daily Recommendation listed is specific to the LPI based on extensive review of the scientific evidence. The Institute of Medicine's Recommended Dietary Allowance (RDA) is 600 IU (15 micrograms)/day for males and females who are 4-70 years old, and 800 IU (20 micrograms)/day for all adults over 70. 2) Vitamin D is considered a "Nutrient of Public Health Concern" because underconsumption is linked to adverse health outcomes. 3) More than 90% of Americans do not meet the dietary requirement for vitamin D. 4) our bodies make vitamin D upon skin exposure to UVB radiation from the sun. Darker skin color, northern latitude, and older age impede the amount of vitamin D produced.

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Vitamin E

What it does

General

  • Vitamin E (also known as alpha-tocopherol) is a fat-soluble vitamin that functions as an antioxidant in lipid (fat) environments.
  • Vitamin E is an important antioxidant nutrient in cell membranes, where it functions to protect cells from oxidative damage.

Cognition-specific

  • Nerve cells are rich in long-chain polyunsaturated fatty acids, a type of lipid that is prone to oxidative damage. Vitamin E has a key role in preventing oxidant-induced lipid damage and is therefore vital in maintaining the integrity of nerve cell membranes.
What we know
  • Some observational studies have found that higher intakes of vitamin C and vitamin E are associated with a slower rate of cognitive decline in older adults (aged 60 and above). However, the majority of observational studies report no association.
  • Randomized controlled trials have not demonstrated a beneficial effect of vitamin E supplements (alone or combined with vitamin C and β-carotene) on cognitive function in healthy older adults.
  • Closer inspection of the evidence suggests that increased vitamin E intake (through food or supplementation) may protect against cognitive decline in individuals with low dietary intake of vitamin E (less than 6.1 mg/day).
  • Notably, approximately 90% of the US population (aged 4 years and older) is not meeting the dietary requirement for vitamin E.
DEFINITIONS
Antioxidants - compounds that prevent or repair the damage caused by reactive oxygen species.
Reactive oxygen species (ROS) - highly unstable oxygen-containing compounds that react easily with nearby cellular structures, potentially causing damage.
Oxidative damage - damage that occurs when the production of reactive oxygen species exceeds the ability of an organism to eliminate or neutralize them.

For references and more information, see the section on Age-related cognitive decline in the in-depth article on Cognitive Function.

Vitamin E (alpha-tocopherol) Flashcard. Main Functions: 1) Boosts antioxidant defense, 2) Protects cell membranes, and 3) Enhances immune function. Good Sources: vegetable oil, sunflower oil (1 tablespoon), 5.6 mg; nuts (hazelnuts, peanuts), almonds, 1 ounce or 23 almonds, 7.3 mg; avocado, 1 medium-sized, 2.7 mg. Daily Recommendation is 15 mg for all adults. Special Notes: 1) The term "vitamin E" actually refers to a family of eight coupounds. Alpha-tocopherol is the most active vitamin E compound. 2) More than 90% of Americans do not meet the dietary requirement for vitmain E. 3) Synthetic vitamin E (in supplements and fortified food) is less bioavailable than naturally occurring vitamin E from food.

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Flavonoids

What they do

General

  • Flavonoids are a type of phytochemical (a chemical produced by plants) that belong to a class of compounds called phenolics.
  • More than 5,000 varieties of flavonoids have been identified and hundreds of flavonoids can exist in a single food.
  • Many of the biological effects of flavonoids are related to their ability to modulate signaling pathways inside of cells.

Cognition-specific

  • Flavonoids are capable of improving endothelial function (see Endothelial Dysfunction), which may indirectly benefit cognitive function by influencing blood flow to the brain.
  • Certain flavonoids can interact with various receptors on nerve cell membranes, leading to activation of signaling pathways that influence synaptic plasticity.
What we know
  • Habitual consumption of flavonoid-rich food and beverages has been associated with cognitive benefits and a reduced rate of age-related cognitive decline.
  • Several randomized controlled trials have demonstrated that daily consumption of certain flavonoid-rich beverages and food (flavanol-rich cocoa powder, blueberries) improves some measures of cognitive function (including executive function, processing speed, working memory, and verbal fluency) in healthy young adults, older adults, and in individuals with mild cognitive impairment.
DEFINITION
Synaptic plasticity - the capacity to change connections between neurons

For references and more information, see the section on Cognitive function in the Flavonoids article

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Resveratrol

What it does

General

  • Resveratrol is a phytochemical (a chemical produced by plants) that belongs to a class of compounds called stilbenes.
  • Some plants produce resveratrol to protect themselves from UV radiation, infection, injury, and other forms of environmental stress.
  • Resveratrol is naturally found in peanuts, grapes, red wine, and some berries.

Cognition-specific

  • Test tube and animal experiments demonstrate that resveratrol can stimulate the formation of new nerve cells and blood vessels.
  • In experimental models that mimic Alzheimer’s disease, resveratrol can inhibit inflammation and oxidative stress caused by the abnormal accumulation of beta-amyloid protein.
 What we know
  • In humans, orally ingested resveratrol is modified by the digestive tract, greatly reducing the amount and modifying the form of resveratrol that reaches the circulation.
  • Only two small, randomized controlled trials have tested the effect of supplemental resveratrol on cognitive function. One trial reported no effect, the other trial reported an improvement in memory function.
  • At this time, there is insufficient evidence to support a beneficial effect of supplemental resveratrol on cognitive function.
HIGHLIGHT
Supplemental resveratrol at doses of >1,000 milligrams (mg)/day might cause diarrhea or other gastrointestinal disturbances.

For references and more information, see the section on Cognitive decline in the Resveratrol article.

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Soy Isoflavones

What they do

General

  • Isoflavones are a type of phytochemical (a chemical produced by plants) that belong to a class of compounds known as phytoestrogens. Phytoestrogens have weak estrogenic activity, meaning that they might be able to either mimic or block the effects of estrogen inside certain body tissues.
  • Isoflavones are fermented by certain gut bacteria, and the resulting byproducts are thought to exert beneficial health effects.

Cognition-specific

  • In test tube and animal experiments, isoflavones enhance the activity of antioxidant enzymes. An increase in antioxidant activity may protect the brain and nerve cells from oxidative damage.
  • Estrogen receptors are located throughout the brain, including regions that are important for learning, memory, and higher-order cognitive functions.
What we know
  • Overall, the data are controversial regarding the effect of isoflavones on cognitive function.
  • Observational studies have reported both beneficial and detrimental associations between isoflavone intake and cognitive function in various populations.
  • Approximately half of randomized controlled trials report positive effects, while the other half report no effect, of isoflavone supplementation on cognitive function in post-menopausal women.
  • Differences in study design seem to underlie the conflicting results. Important differences that can influence isoflavone study outcomes include:
    • type, dose, and source of isoflavone — for example, fermented soy (tempe) and non-fermented soy (tofu) contain different amounts of isoflavones.
    • duration of observation or treatment period — isoflavones may have an initial, short-term positive effect on cognition that goes away with long-term continuous use.
    • characteristics of the study population — participant age, gender, ethnicity, and years since menopause can influence the response to isoflavone exposure.
  • At this time, there is insufficient evidence to support a conclusive beneficial effect of supplemental isoflavones on cognitive function.
DEFINITIONS
Antioxidants - compounds that prevent or repair the damage caused by reactive oxygen species.
Reactive oxygen species (ROS) - highly unstable oxygen-containing compounds that react easily with nearby cellular structures, potentially causing damage.
Oxidative damage - damage that occurs when the production of reactive oxygen species exceeds the ability of an organism to eliminate or neutralize them.

For references and more information, see the section on Cognitive decline in the Soy Isoflavones article.

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Alcoholic Beverages

What they do

General

  • Alcoholic beverages contain ethanol and other ingredients with bioactive properties that may affect health.
  • When consumed in moderation (no more than two drinks/day for men and one drink/day for women), alcoholic beverages have been associated with beneficial effects in the cardiovascular system.

Cognition-specific

  • Chronic alcohol abuse has negative effects on the central nervous system. This may be due to malnutrition (in particular deficiencies in the B vitamins [see Table 1]), toxic effects on certain neurons, and damage to brain structures.
  • Moderate alcohol consumption is associated with cardiovascular benefits (see Coronary Heart Disease), which may also benefit cognitive health.
What we know
  • Alcoholism and heavy alcohol consumption (>3-4 drinks/day) increases the risk of cognitive impairment and dementia. Cognitive impairment mainly involves deficits in memory and executive functions.
  • Light-to-moderate alcohol consumption in adults over 55 years of age has been associated with a reduced risk of cognitive impairment compared to nondrinkers.

For references and more information, see the section on Cognitive decline, dementia, and Alzheimer's disease in the Alcoholic Beverages article.

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Tea

What it does

General

  • Tea is an infusion of the leaves of the Camellia sinensis plant and includes white, green, oolong, and black teas. This summary does not discuss herbal teas, which are infusions of herbs or plants other than Camellia sinensis.
  • Tea contains a number of bioactive substances, including caffeine, fluoride, and flavonoids, which may exert beneficial health effects.

Cognition-specific

  • Tea is particularly rich in catechins, a type of flavonoid that has been shown to improve endothelial function; improved endothelial function may indirectly benefit cognitive function by influencing blood flow to the brain. 
  • Caffeine binds to certain nerve cell receptors, leading to stimulatory effects in the nervous system.
What we know
  • Observational studies suggest that higher intake of tea is associated with better cognitive function and a reduced risk of cognitive decline.
  • A few, small, randomized controlled trials suggest that black tea consumption may improve attention and alertness; although some components in tea may have acute effects, most of the improvements appear to be due to caffeine.

For references and more information, see the section on Cognitive function in the Tea article.

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This content was underwritten, in part, by a grant from Bayer Consumer Care AG, Basel, Switzerland.