The human brain has high energy and nutrient needs. Changes in energy or nutrient intake can alter both brain chemistry and the functioning of nerves in the brain. Various components of the diet can alter the brain’s internal processes and thereby exert a perceivable and measurable impact on energy levels, cognitive performance and mood. Glucose is the preferred source of energy for proper brain functioning, but micronutrients are also vitally important co-factors for the brain’s energy yielding metabolism. Other dietary components affect mental energy through their effects on neurotransmitters, blood flow in the brain and the metabolic basis of thought.
The science of mental energy
Mental energy can be defined as the perception of mental alertness, high mood levels and motivation and the metabolic processes that support the brain. A model accounting for cognition, mood and motivation has been proposed to describe mental energy (1).Cognition is a combination of attention, vigilance and a high ability to perform mental tasks. Mood is related to separate feelings of energy and fatigue. Motivation is the determination and enthusiasm to perform mental tasks. These areas of mental energy can be measured with questionnaires, specific mental tests and by examining brain activity.
The brain demands a large amount of energy around 20% of our daily energy consumption (2). A large portion of this energy is consumed by the neurons, because a fuel source is required to send the electrical signals required for the process of thought. Brain waves mark changes in the state of consciousness from active thought through to quiet relaxation and then to deep sleep. An electroencephalogram (EEG) allows scientists to measure brain waves and can be used to determine the state of relaxation and quality of sleep. By recording brain wave activity, it is able to objectively measure levels of alertness. Two important measures of brain energy, quantified by electroencephalography (EEG), are beta-waves (indicative of an alert and concentrated brain) and alpha-waves (a quiet, contemplative state).
Intake of energy and several different nutrients affects levels of chemicals in the brain called neurotrans-mitters. Neurotransmitters transmit nerve impulses from one nerve cell to another and they influence mood, sleep patterns and thinking. Deficiencies or excesses of certain nutrients can damage nerves in the brain, causing changes in memory, limiting problem-solving ability and impairing brain function. Several nutritional factors can influence mental health, including: overall energy intake, intake of the energy-containing nutrients (proteins, carbohydrates, and fats), alcohol intake and intake of vitamins and minerals. Often, deficiencies of multiple nutrients rather than a single nutrient are responsible for changes in brain functio-ning.
B vitamins are a group of water-soluble compounds that, along with fulfilling other important metabolic functions, help the body obtain or create energy from food. Vitamin B1 (thiamin) is extremely important for the brain because it facilitates glucose processing, thus ensuring energy production, and is also needed to make several neurotransmitters. It has been shown that vitamin B1 modulates cognitive performance (3), particularly in the elderly (4). Individuals with a thiamin deficiency can develop mental disorders (charac-terized by confusion, mental changes, abnormal eye movements and unsteadiness) that can develop into severe memory loss. Vitamin B3 (niacin) is involved in releasing energy into the body from carbohydrates, proteins and fats (5–7). Niacin deficiency produces many mental symptoms such as irritability, headaches, loss of memory, inability to sleep and emotional instability. Vitamin B6(pyridoxine) is needed by the body to produce most of the brain's neurotransmitters. High levels of vitamin B6 in the blood have been associated with improved performance in memorization tests (8). Although rare, vitamin B6 deficiency is characterized by mental changes such as fatigue, nervousness, irritability, depression, insomnia, dizziness and nerve changes. Folic acid is involved in protein metabolism in the body and in the metabolism of some amino acids. A deficiency can lower levels of the neurotransmitter serotonin in the brain (9). Vitamin B12 (cobalamin) is needed to maintain the outer coating (myelin sheath) of nerve cells. Inadequate myelin results in nerve damage and impaired brain function. Adequate intake of vitamins B6 and B12 is related to memory performance and has been linked with better memory functioning (10). Vitamin B12 deficiency can go undetected in individuals for years, but it eventually causes irreversible nerve damage, dementia and brain atrophy. The B vitamins riboflavin, vitamin B6, vitamin B12 and folic acid work together as co-factors in DNA and protein synthesis. They are crucial for the metabolism of carbohydrates, for cell proliferation and for the formation of red blood cells. In a randomized controlled trial, where high doses of B vitamins were administered to healthy males, improvements were shown in perception of vigor and ratings of energy during cognitive testing (11).
Antioxidant vitamins have numerous roles. In particular, they neutralize the active and toxic forms of oxygen and scavenge free radicals. They are thought to protect unsaturated fatty acids against peroxidation and thus contribute to maintaining the integrity and stability of cellular structures in the brain. Acting in the lipid phase, they form part of a vast, complex and interactive protective system involving beta-carotene, vitamin A, vitamin C and various enzymes that function with selenium, copper, zinc and manganese.
Vitamin A seems to influence synaptic plasticity in the hippocampus, suggesting it has a role in the establishment and maintenance of cognitive functions (12). Its precursor beta-carotene contributes to the stabilisation of membranes. Vitamin C is required to transform the neurotransmitter dopamine into noradrenaline. Some researchers have suggested that there is a relationship between the blood level of vitamin C and the intelligence quotient, namely an increase of four IQ points when the plasma concentration of vitamin C is increased by 50%. Indeed, some of the elements used in tests to determine non-verbal IQ were altered as a result of the serum concentration of vitamin C (13). Besides its antioxidant efficacy, vitamin E (alpha-tocopherol) also seems to play a role at the level of cognitive functions (14).
In a randomized controlled trial, healthy college students ranging in age from 17 to 27 received supplements of antioxidant vitamins C (600 mg/day) and E (100 mg/day) or a placebo over a period of one year (15). Cognitive performance (including attention, vigilance and response speed) was assessed at the beginning of the study and then again at 3 months and at the end of the year. The study results showed that female participants who received supplements showed improved cognitive performance. After 3 months, when the serum levels of the vitamins had reached a plateau, the differences between the vitamin and placebo groups no longer reached significance.
It has been suggested that the effects of antioxidant vitamins can be beneficial for neural functioning, espe-cially with regard to age-related neural decline. Antioxidants may also improve cardiovascular function, and this may help prevent cardiovascular events that have negative consequences on memory. Consequently, antioxidants would theoretically appear to be useful in forestalling or slowing age-related memory decline. In one such study, participants aged 60 and over showed a significant relationship between increased blood concentration levels of vitamin E and improved memory performance (16).
To date, the few placebo-controlled human studies that have been conducted have reported no consistent beneficial effects of antioxidant treatment (specifically vitamin E) on attention or memory. The results based on human studies may be too preliminary to justify the conclusion that antioxidants are not useful for maintaining memory function (17). Many issues warrant more research. Firstly, beneficial effects might emerge in healthy older adults with age-associated memory decline (and not as tested in Alzheimer’s disease or early Parkinson’s disease patients). Also, because antioxidants work together as a system, their effectiveness can depend on levels of other vitamins and minerals. Moreover, intake of an antioxidant may not directly translate into serum levels. Finally, certain neural systems may be particularly affected by aging and particularly vulnerable to lifelong oxidative stress. Cognitive and memory tests that are most sensitive to the functioning of these “at risk” neural systems would be most likely to show possible benefits of antioxidants.
Coenzyme Q10 is a vitamin-like substance produced by the body and required for energy production at the cellular level. It is found in organs with a high energy demand, including the heart and brain. Coenzyme Q10 levels decrease during aging. The amount supplied by a normal diet is low compared to the amount made by the body, so declines in coenzyme Q10 production cannot easily be offset by food alone (18).
In addition, there is evidence that coenzyme Q10 and vitamin E (alpha-tocopherol) act together as antioxi-dants to scavenge radicals, particularly in the mitochondrial inner membrane (19). Based on animal studies, increased coenzyme Q10 intakes have been linked with improved cognitive functions, upregulated mitochondrial function and facilitated energy production (20).
Essential fatty acids
Long-chain omega-3 polyunsaturated fatty acids are well known for their effects on cognition. They are indisputably important for several biological functions of brain cells. The three main omega-3 fatty acids are alphalinoleic acid (ALA), eicosapentaenoic acid (EPA) and docosohexaenoic acid (DHA). They are the building blocks and signaling molecules in brain cell membranes. Omega-3 fatty acids regulate glucose uptake in the brain and DHA supports normal brain functioning (21).
The effects of essential fatty acids on mood are supported by nutrition research, although positive effects may only be noticeable after medium-term supplementation. In a diet-related study, increasing levels of omega-3 fatty acids through the diet was shown to improve mood (22). A large clinical trial involving older adults showed that DHA supplemented over 6 months improved learning and episodic memory scores (23). High levels of EPA were associated with an active mental state and good blood circulation in the brain (24). Increased omega-3 fatty acid intakes have shown to reduce the risk of atherosclerosis, which can decrease blood flow to the brain, impairing brain functioning (25). Though omega-3 fatty acids appear effective in the prevention of stress, their role as a mood regulator is a matter for discussion pending experimental proof in animal and human models (26).
Minerals and trace elements
Magnesium is required for over 300 enzymes in the body and contributes to neurotransmitter release and the ability of brain cells to form new connections, contributing to normal cognitive function (27). Some recent preliminary research indicates that increasing brain magnesium levels may improve learning and memory, especially during aging (28, 29). Magnesium deficiency can cause restlessness, nervousness, muscular twitching and unsteadiness.
It is evident that iron modulates cerebral development (30), and the relationship between iron status and cognitive performance is attracting interest (31). Iron is essential for formation of hemoglobin, the substance that carries oxygen to cells throughout the body. Iron deficiency eventually leads to anemia, whereby insufficient oxygen reaches the brain. Anemia can cause fatigue and impair mental functioning. Iron deficiency during the first two years of life can lead to permanent brain damage. During aging, trace elements such as iron help to protect cognitive function (32).
Zinc is an essential component of many enzymes (particularly antioxidant enzymes) of the immune system and the brain. It contributes to normal cognitive function and has been shown to improve cognition in middle-aged participants (33). Zinc is also part of the mechanisms which detect taste and smell. It is necessary for the function of the brain regions that perceive and interpret the pleasures of eating (34). Zinc deficiency may impair whole-body accumulation of polyunsaturated fatty acids (35), thus affecting brain supply. Consequently, zinc deficiency induces behavioral changes.