AA (arachidonic acid)

One of the omega-6 series of fatty acids, its chemical formula is C20H32O2. In the human diet, AA is found in animal products such as milk, red meat and eggs, and it can also be synthesised from the essential fatty acid LA. AA is an important component in the muscles, where it is converted to prostaglandins which aid muscle growth, so AA is used as a supplement by bodybuilders. It’s also essential to brain function, where it acts as a signalling molecule, and plays a key role in the biochemical processes which produce inflammation.

Action potential

The primary electrical signal generated by neurons. Action potentials may also be referred to as ‘spikes’, ‘firing’, ‘signalling’ or ‘neuronal activity’.

ALA (alpha-linolenic acid)

One of the omega-3 series of fatty acids, considered an essential fatty acid because it cannot be synthesised by the human body. Its chemical formula is C18H30O2. In the human diet, ALA is found in plant extracts, particularly in oils like linseed and rapeseed. In the body, it is converted to omega-3 fatty acids such as DHA and EPA which are critical for brain function.

Alzheimer’s disease

A form of dementia, usually but not always associated with the elderly. At present incurable, it is particularly associated with memory loss and, at more severe stages, behavioural disturbances, loss of speech, and disruption of basic functions such as walking and eating. Brain scans of patients with Alzheimer's show spreading neurodegeneration, particularly in areas of the brain linked to memory, such as the hippocampus and frontal cortex. Analysis of post-mortem brains shows a build-up of two proteins, beta-amyloid and tau, though it is not yet known whether these have a causal role in the disease or are consequences of other processes.


In neurons, the axon is the large filament extending from the cell body, which transmits the action potential (the neuron’s output signal) to synapses, and thence to other neurons or to specialised structures such as the neuromuscular junctions, which control muscle contraction. Axons from cells in the spinal cord may reach a metre or more in length (if, for instance, their destination is the big toe). In the brain, white matter is primarily made up of bundles of axons (‘fibre tracts’), while grey matter consists of neuron cell bodies.


A bioactive chemical is one which, at the dose given, exerts noticeable effects in the human body.


A form of fat, chemical formula C27H46O, obtained in human diet from animal sources such as meat and eggs. Unlike fatty acids, cholesterol has a structure made up of multiple rings, rather than a chain, of carbon atoms. Like fatty acids, cholesterol is an essential part of cell membranes. Excessive cholesterol, however, is thought to damage the body by accumulating in the arteries, contributing to cardiovascular disease. Because cholesterol is a fat, it is hydrophobic (repels water). Since blood is water-based, cholesterol thus requires a specific transport mechanism to move around the body. Specialised lipoproteins attach to the cholesterol molecule, forming particles of varying sizes which can be carried in the bloodstream. The largest particles, formed by high density lipoproteins (HDL), are associated with healthier heart and cardiovascular function than are the smaller, low density lipoproteins (LDL). Thus the cholesterol carried by HDL and LDL is often called, respectively, 'good' and 'bad' cholesterol.

Cochrane review

A rigorous systematic review of the scientific literature on a particular topic, widely recognised as a gold standard by researchers.

Cohort study

A research study which follows a group of people (the cohort) over time. For example, researchers who hypothesise that oily fish protects against heart disease might assess cohort members’ consumption of oily fish at baseline (at the beginning of the study) and at intervals throughout the study, observe how many cohort members developed heart disease during the study, and analyse their data to see whether heart disease was more prevalent among participants with lower fish consumption.


The wrinkled outer layer of the brain. Traditionally, capacities like intelligence, consciousness and logical thought have been attributed to the cortex, while more basic functions such as emotions and control of breathing and heart rate were assigned to subcortical structures like the amygdala and brainstem, though this is now seen as oversimplified. The cortex is divided into two halves, or hemispheres, connected by the corpus callosum, a large bundle of nerve fibres. Each hemisphere has its own specialised functions. In most people, for example, the left hemisphere controls language. Each hemisphere is further divided into four lobes: the occipital lobe (associated with visual processing), the parietal lobe (associated with perceptions of body and space), the temporal lobe (associated with hearing and object identification), and the frontal lobe (associated with movement, short-term memory and reasoning).


In neurons, dendrites are branch-like filaments extending from the cell body, along which incoming electrical signals flow. These converge on the neuron’s cell body, where an action potential may be triggered as a result. Incoming stimuli may come from other neurons, or from specialised structures like the photoreceptors in the human eye, which convert light into electrical signals.

DHA (docosahexaenoic acid)

One of the omega-3 series of fatty acids, its chemical formula is C22H32O2. It can be synthesised in the body from ALA, or obtained from oily fish like salmon and herring. DHA is considered particularly important for brain and visual function, and is thought to have anti-inflammatory properties.

DNA (deoxyribonucleic acid)

The material from which genes are built.

Double-blind trial

In clinical trials of a potential treatment, the treatment is often tested alongside a similar, placebo (dummy) treatment. Some participants receive treatment, and some placebo. For example, trials of fish oil supplementation may use another oil (e.g. safflower) as a placebo. Ideally, the treatment and placebo capsules will look and taste the same. The trial is ‘blind’ if the participants do not know whether they are getting the treatment or the placebo. It is ‘double-blind’ if neither the participants nor the experimenters who give them the capsules know who is getting what. Double-blind trials are preferred, since they reduce the chances of the experimenters’ expectations unconsciously biasing the results.

EPA (eicosapentanoic acid)

One of the omega-3 series of fatty acids, its chemical formula is C20H30O2. It can be synthesised in the body from ALA, or obtained from oily fish like salmon and herring. EPA is considered particularly important for brain and heart function, and is thought to have anti-inflammatory properties.


The study of where and when diseases occur. Identifying patterns of disease can point towards likely causes. Epidemiological studies by Sir Richard Doll and colleagues, for example, identified associations between lung cancer and smoking and eventually led to the recognition that smoking causes lung cancer.

Essential fatty acid

A fatty acid which must be supplied in the diet, since it cannot be synthesised by the body. For humans, only ALA (omega-3) and LA (omega-6) are considered essential.

Fatty acids

Forms of fat used by parts of the human body for fuel (though not the brain, which uses glucose). Insoluble in water, they are an important component of brain cell membranes, which isolate the cell’s operating machinery from its environment and allow it to transmit electrical signals. They have the form of a chain of carbon atoms, varying in length (hence some are called long-chain fatty acids), and with hydrogen and oxygen atoms attached.


Not all brain cells are neurons. Glial cells were traditionally thought to act as a support system for neurons, but they are now increasingly recognised as playing an important role in neurotransmission and also in brain inflammation.

Grey matter

See Axons.


A set of biochemical processes which evolved to protect the body against injury and disease. When inflammation occurs acutely (over a short time) it is  generally beneficial, but chronic inflammation is a feature of many of today's commonest disorders, from obesity, arthritis, diabetes and cancer to Alzheimer's disease, multiple sclerosis and stroke. The omega-6 fatty acid AA is considered central to pro-inflammatory pathways, while omega-3 fatty acids like DHA and EPA are thought to have anti-inflammatory effects. Some researchers have therefore proposed that typical Western diets, which have very high omega-6 to omega-3 ratios, may be contributing to modern forms of ill-health.

LA (linoleic acid)

One of the omega-6 series of fatty acids, considered an essential fatty acid because it cannot be synthesised by the human body. Its chemical formula is C18H32O2. In the human diet, LA is found in animal and vegetable fats, as well as in fish. In the body, it is converted to omega-6 fatty acids such as AA which are critical for brain function.




A biochemical term for fat.

Metal chelators

Molecules which form chemical bonds with metals, such as iron and zinc. In medicine, understanding how metals function in the body is important for many conditions, such as anaemia due to iron deficiency, and requires an understanding of how the metal chelators behave.


A chemical which is needed for the human body to function, but which is only needed in small amounts. Trace minerals such as zinc, selenium and lithium, fatty acids such as DHA and EPA, and vitamins are examples of micronutrients.

MRI (magnetic resonance imaging)

Magnetic resonance imaging, a technique for scanning living brains which uses magnetic fields and radio pulses to distinguish different kinds of material within the skull (such as grey matter, white matter, and blood). Structural MRI scans (MRI) reveal the architecture of the brain and can be used for detecting abnormalities such as tumours. Functional MRI scans (fMRI) monitor blood flow, which is thought to reflect brain activity.


A collective term for destructive processes in the brain which gradually destroy brain tissue. Neurons and/or glia may be affected. The degeneration may begin with damage to synapses, dendrites and axons, but in severe cases (such as advanced Alzheimer's) large numbers of neurons die off and brain shrinkage is clearly visible on structural MRI.


The archetypal brain cell, which generates an electrical signal, the action potential, in response to stimulation. Neurons have a central cell body, which contains their DNA and operating machinery. From the cell body extend the dendrites and axon through which the neuron communicates with other neurons via synapses.


The essential process by which neurons transmit signals through the brain and central nervous system, allowing the body to react to internal and external stimuli. Neurotransmission involves both electrical signals (within each neuron) and chemical signals (between neurons). These signals are thought to underlie all human functions, from sensation and movement to conscious experience.


Substances such as dopamine, serotonin, glutamate and GABA, used by neurons to communicate across synapses.


A food or food supplement used with the aim of providing additional health benefits. The contrast is with pharmaceuticals – chemicals used purely for their health benefits.

Omega-3 (aka n-3) fatty acids

A series of polyunsaturated fatty acids, so-called because their carbon chains have multiple double bonds. In omega-3 fatty acids like EPA (chemical formula C20H30O2) the first double carbon bond is located between the third and fourth carbon atoms, counting from the ‘n’ end of the carbon chain – that is, the end without the oxygen atoms.

Omega-6 (aka n-6) fatty acids

A series of polyunsaturated fatty acids, so-called because their carbon chains have multiple double bonds. In omega-6 fatty acids like a the first double carbon bond is located between the sixth and seventh carbon atoms, counting from the ‘n’ end of the carbon chain – that is, the end without the oxygen atoms.


A ‘dummy’ treatment, such as a sugar pill. Placebos are used in clinical trials, in comparison with a genuine treatment, to test whether the treatment is effective. By giving a placebo, researchers can control for any effects due to patient expectations (the ‘placebo effect’), such that any observed effects are due to the treatment itself, and independent of a person's awareness that they are being treated. To be effective, placebos must be as similar as possible to the treatment.

Polyunsaturated fatty acids

See Saturated/unsaturated fat.


In research, a study of the relationship between two variables, such as fish consumption and cognitive function, may be done prospectively or retrospectively. A retrospective study might assess participants' cognitive function, and in the same session ask them to report how much fish they ate. A prospective study might assess their cognitive function and their fish consumption at baseline (initially), and then again at intervals throughout the study. Because human memory is fallible, prospective studies are generally considered better than retrospective studies.


A randomised controlled trial, regarded as the highest standard of medical research. Participants in such trials are assigned to treatment and control (or placebo) groups at random. The aim is to avoid unconscious experimenter bias and to reduce the chances of the participants’ characteristics (e.g. age, gender, educational background) differing between groups, so that as far as possible, the only difference between the groups is the treatments they receive.


Specialised proteins which sit in a cell’s surface membrane and which are activated only by certain substances. When one such molecule approaches, it forms chemical bonds with the receptor which force it to change shape. That change triggers further biochemical processes within the cell. In neurons, receptors can be excitatory (their activation makes the neuron more likely to fire an action potential) or inhibitory (reducing the chance of an action potential).

Risk factor

Anything whose presence is thought to make a particular disease, condition or behaviour more likely. For example, being male is considered a risk factor for violent behaviour, while being female is considered a risk factor for anxiety and depression. Protective factors are associated with reduced risk

Saturated/unsaturated fats

The terms relate to the kind of chemical bonds which exist between the carbon atoms in the fatty acid carbon chain. Each carbon atom can form up to four single bonds with other atoms, such as hydrogen, and a fat where all the carbon bonds are single is described as saturated. However, carbon atoms can also form double bonds with other carbon atoms, and fats with such bonds are described as unsaturated. Unsaturated fats can be either mono- or polyunsaturated, depending on whether they have one or more double bonds.


The tiny gaps between one neuron and another, across which a chemical signal is sent. When an action potential, transmitted from the cell body along the axon, reaches the synapse, it triggers the release of small quantities of neurotransmitter into the synaptic gap. These then activate receptors on nearby neurons.


Vitamins are a kind of micronutrient essential to human health, though in smaller quantities than other micronutrients such as fatty acids. They are organic compounds; that is, they are built from carbon, hydrogen and oxygen. Some vitamins are toxic in excess.

White matter

See Axons.