Glossary

Acetylcholine is a signaling chemical in the brain that changes how excitable neurons are, how they pass signals across synapses and how groups of neurons fire together, the classic role of a neuromodulator.

Acetylcholinesterase (AChE) is an enzyme that breaks down the chemical messenger acetylcholine into choline and acetic acid, clearing it from the gap between nerve cells after a signal has passed. It ranks among nature's most efficient enzymes.

Actigraphy estimates sleep and wakefulness from movement recorded by a wrist-worn device, which scores each 30-second slice of the night as sleep or wake.

Adenosine is a substance the body makes that is widely accepted as a regulator of sleep. It likely drives the sleepiness that builds during long periods awake, and caffeine works by blocking its receptors.

An adverse event is any unwanted medical occurrence in a person using a product, whether or not the product caused it; a suspected adverse reaction is an adverse event with a reasonable possibility that the product caused it.

An amino acid is an organic molecule that generally contains an amino group and a carboxyl group. Twenty alpha-amino acids are the subunits that link together to form proteins.

The ARTG (Australian Register of Therapeutic Goods) is the register of medicines, medical devices and biologicals that can be supplied in Australia; registered and listed goods each get a unique registration or listing number.

Attention is the set of brain processes that keep a person alert and select which input to prioritize. Sustained attention must hold over time and fluctuates; selective attention focuses on a chosen input and suppresses others.

BDNF (brain-derived neurotrophic factor) is a protein that supports the development and survival of nerve cells and appears essential to synaptic plasticity, the strengthening and weakening of connections between neurons.

The blood-brain barrier is the set of properties of the blood vessels in the brain and spinal cord that tightly control which ions, molecules and cells pass between the blood and the brain.

A certificate of analysis (COA) is a document that reports the test methods used, the limits applied and the actual results for a tested material, such as an ingredient a supplier ships to a manufacturer.

Choline is an essential nutrient. The body uses it to make the chemical messenger acetylcholine and phospholipids, the fats that keep cell membranes intact, and as a methyl donor after converting it to betaine.

A circadian rhythm is a biological cycle that repeats about every 24 hours, such as the sleep-wake cycle. It is driven by an internal clock in the brain, which bright daylight keeps in step with the outside day.

Cognitive load is the demand a task places on working memory, which can only process a limited number of information elements at any given time. When the load exceeds a person's capacity, performance and learning suffer.

A confidence interval is a range around a study's estimate, usually set at 95%, covering the effect sizes more compatible with the data than those outside it, if the assumptions behind the analysis hold.

A contraindication is a situation in which a product should not be used because the risk clearly outweighs any possible benefit, such as use by people of a particular age, sex or condition, or alongside another therapy.

Cortisol is the main glucocorticoid hormone in humans. The adrenal glands release it at the end of the hypothalamic-pituitary-adrenal (HPA) axis, a stress-response chain, and it helps regulate metabolic, cardiovascular, immune and behavioral processes.

Creatinine is a waste product formed when creatine phosphate in muscle breaks down, and dietary protein digestion also produces it. Its level in the blood is used as an indicator of kidney function.

A crossover trial is a randomized study in which each participant receives two or more interventions in turn, such as a supplement and then a placebo, so that each person serves as their own comparison.

Cytochrome P450 (CYP) enzymes are a family of membrane-bound proteins that carry out much of the body's metabolism of medicines; inhibiting or inducing them is a major mechanism behind drug interactions.

Dopamine is a neurotransmitter made in the brain and in the rest of the body. It acts on G protein-coupled receptors and has roles in movement control, motivation, reward and cognitive function.

Dose-response is the relationship between the amount of a substance given and the size of the response measured. Dose-response studies can help identify a dose beyond which more is unlikely to bring further benefit.

A double-blind trial keeps both participants and investigators, usually including those who assess outcomes, unaware of who received the intervention and who received the comparison, so that this knowledge cannot sway the results.

DSHEA is the Dietary Supplement Health and Education Act of 1994, the US law that amended the Federal Food, Drug, and Cosmetic Act to create a regulatory framework for dietary supplements.

An effect size is a number that expresses how large a difference or relationship is, such as the gap between a supplement group and a placebo group, rather than only whether a result was statistically significant.

Elemental magnesium is the weight of the magnesium itself in a supplement, not the weight of the whole compound, such as magnesium oxide or citrate, that carries it. US Supplement Facts labels declare the elemental amount.

Executive function is a family of top-down mental processes used when a person has to concentrate and pay attention rather than go on automatic. Its core parts are inhibition, working memory and cognitive flexibility.

Flavanols, also called flavan-3-ols or catechins, are a subclass of flavonoids. Cocoa is rich in them, and studies have measured them after people ate tea, cocoa, apples, grapes and nuts.

Flavonoids are a group of plant compounds with a polyphenolic structure. They are found in fruits, vegetables, grains, bark, roots, stems, flowers, tea and wine.

Flow-mediated dilation (FMD) is a noninvasive test of how much a large artery widens when blood flow through it increases, used in research as a marker of how well the artery's inner lining works.

A fruiting body, or carpophore, is the reproductive part of a fungus. It is the part seen as the mushroom, and it develops from the mycelium and produces the spores.

GABA (gamma-aminobutyric acid) is the main inhibitory neurotransmitter in the brain's cortex. It damps down nerve-cell activity and balances glutamate, the main excitatory neurotransmitter.

Ginsenosides are triterpene saponins, also called ginseng saponins, found almost exclusively in Panax species and concentrated in the roots. They are regarded as the major active constituents of Panax ginseng.

Glutamate is the brain's primary excitatory neurotransmitter, the main chemical signal that activates nerve cells. Neurons and support cells called astrocytes recycle it extensively through the glutamate-glutamine cycle.

GRAS (generally recognized as safe) is a US status for a substance added to food: qualified experts generally recognize it as safe under its intended conditions of use, so it is not treated as a food additive.

A hazard ratio says how many times more or less likely an event is, at a given point during follow-up, in one group than in a comparison group, in studies that record when events happen.

Hepatotoxicity is liver injury caused by a chemical, such as a medicine, herb or dietary supplement; sources separate raised liver enzymes on blood tests from clinically apparent liver injury, which can bring jaundice.

An interaction is a change in how a supplement or medicine acts when it is combined with another, either in how much reaches the body or in the combined effect, and it can raise the risk of adverse events.

A label claim is the amount of an ingredient that a product's label says each serving contains. Laboratory tests compare the measured amount with it to judge whether a product matches its label.

Lean mass is body mass minus fat. An international working group on body-composition terms counts it as the same thing as fat-free mass, which includes bone mineral, and distinguishes it from skeletal muscle.

Magnetic resonance spectroscopy (MRS) is a noninvasive scan that measures the levels of chemicals, called metabolites, in living tissue such as the brain or a muscle.

Mental fatigue is a psychobiological state caused by prolonged periods of demanding cognitive activity. One framework links it to the point where the energy a task costs seems to outweigh its expected rewards.

A meta-analysis is the statistical combination of results from two or more separate studies, giving one pooled estimate of the effect.

Mitochondria are organelles: membrane-bound structures inside the cells of most eukaryotes. They are the sites of oxidative phosphorylation, the reactions that form ATP, the molecule cells use as an energy currency.

Mycelium is the vegetative, thread-like body of a fungus, made of fused cell filaments that spread through the growth medium to collect nutrients. Together the filaments form an interconnected three-dimensional network.

A narrow therapeutic index (NTI) drug is one where small differences in dose or blood concentration may lead to serious therapeutic failures or to adverse reactions that are life-threatening or cause persistent or significant disability, as the FDA defines it.

Nerve growth factor (NGF) is a protein in the neurotrophin family, signals that regulate how nerve cells develop, survive and work. It was the first neurotrophin to be discovered.

Neurogenesis is the generation of new nerve cells (neurons) from dividing precursor cells. Adult hippocampal neurogenesis is this process in the hippocampus, a brain region central to learning and memory. NootropicsWork classes it as a mechanism.

Neuroplasticity is the brain's ability to reorganize and modify its neural connections in response to experience, learning, injury and the environment.

A neurotransmitter is a signaling molecule that nerve cells release, when stimulated, to pass a message to other cells nearby or farther away. Neurotransmitters range from gases and amino acids to larger peptides.

An NMDA receptor is a type of glutamate receptor: an ion channel on nerve cells that opens only when glutamate and a second molecule, glycine or D-serine, both bind. It takes part in synaptic plasticity, learning and memory.

A nootropic is a substance claimed to improve cognition, such as memory, attention or learning. The word dates from 1972 and is used for drugs and supplements; a 2022 review found the efficacy of cognitive-enhancing drugs in healthy people uncertain.

Norepinephrine, also called noradrenaline, is a chemical messenger (neurotransmitter) in the brain. Most of the norepinephrine released in the brain comes from the locus coeruleus, a small nucleus in the brainstem linked to attention and arousal.

In the EU and the UK, a novel food is a food that was not used for human consumption to a significant degree there before May 15, 1997. It needs authorization before it can be sold.

An NPN (Natural Product Number) is the eight-digit product license number Health Canada assigns to a licensed natural health product, shown on the label after the letters NPN.

A nucleoside is a molecule made of a purine or pyrimidine base attached to a sugar, either ribose or deoxyribose. Adding a phosphate group to a nucleoside makes a nucleotide.

A nucleotide is a nucleoside joined to phosphate: a purine or pyrimidine base, a pentose sugar and a phosphate group. Nucleotides are the units from which DNA and RNA are built.

The omega-3 index is the amount of two omega-3 fatty acids, EPA and DHA, in red blood cells, expressed as a percentage, and is used as a marker of long-term EPA and DHA intake.

The one-repetition maximum (1RM) is the heaviest weight a person can lift once with correct technique in a given exercise, and it is a commonly used field test of muscular strength.

An open-label trial is one in which participants know which intervention they are receiving, because it is not hidden by blinding or a matched placebo; outcome assessors may still be kept unaware.

Perceived stress is how stressful people judge their own lives to be. It is most often measured with the Perceived Stress Scale (PSS), which asks how far people appraise situations in their lives as uncontrollable and overloaded.

Phosphatidylcholine (PC) is a phospholipid with choline as its head group. With phosphatidylethanolamine, it is the most abundant phospholipid in mammalian cell membranes, and making it is the main fate of choline in the body.

A phospholipid is a fat molecule that carries a phosphate group. Glycerophospholipids are the main lipids in cell membranes; common examples include phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine.

A placebo is a dummy version of an intervention, matched to the real product in features such as taste, color and size, that trials use as a comparison so participants and researchers cannot tell who got what.

Polyphenols are abundant micronutrients in the human diet, with hundreds of different compounds grouped into several classes. Flavonoids are one class of plant compounds with a polyphenolic structure, found in fruits, vegetables and certain beverages.

Polysomnography (PSG) is an overnight sleep study that records brain waves, eye movements, muscle activity, heart rhythm, blood oxygen, airflow and breathing effort to measure sleep in detail.

Pre-registration is the public recording of a trial's plan, including its primary outcomes, in a trial registry such as ClinicalTrials.gov before the first participant is enrolled, so that readers can check the published report against the plan.

Processing speed is the speed with which a person can carry out mental processing operations. Timed coding tasks such as the Digit Symbol Substitution Test are a common measure of it.

A proprietary blend is a group of nonnutrient dietary ingredients listed together under one name on a US supplement label, with the total weight of the blend declared but not the amount of each ingredient in it.

A randomized controlled trial (RCT) is a study in which chance decides whether each participant receives the intervention being tested or a comparison, such as a placebo, so that the groups start out alike on average.

Reaction time is how long a person takes to respond to a stimulus. Simple reaction time, the minimal time needed to respond to a stimulus, is a basic measure of processing speed.

A receptor is a molecule on or inside a cell that recognizes a specific chemical signal, such as a neurotransmitter or a hormone, and links it to a response in the cell. Receptors are also the targets of many drugs.

A rhizome is an underground stem. In Rhodiola rosea, the rhizome is the part of the plant used medicinally, and regulators list the root and rhizome together as the plant part.

Risk of bias is a judgment of how likely it is that flaws in a study's design, conduct or reporting have pushed its result away from the truth, rated in Cochrane's tool as low, some concerns or high.

Serotonin (5-hydroxytryptamine, or 5-HT) is a neurotransmitter in the brain and a hormone in the rest of the body. The body makes it from the essential amino acid tryptophan.

Sleep latency is the time it takes to fall asleep. Diagnostic sleep studies end it at the first scored epoch of sleep, while questionnaires and other self-reports rely on people's own estimates.

A standardized mean difference (SMD) is the difference between two group averages divided by a standard deviation, so results measured on different scales can be pooled in one meta-analysis.

A result is called statistically significant when its P value falls at or below a preset cut-off, usually 0.05. This flags data as unusual under the test's assumptions, not that an effect is large or important.

In the saffron crocus (Crocus sativus), the stigma is the tip of the flower's style, which splits into three threads. Saffron is the commercial name for these red stigmas once dried.

A structure/function claim is a statement on a US dietary supplement label describing how a nutrient or dietary ingredient is intended to affect the normal structure or function of the human body.

A systematic review is a review that uses explicit, systematic methods to find, select and combine the findings of studies that address a clearly formulated question.

Theobromine is a methylxanthine, the same chemical family as caffeine. Together with caffeine, it is one of the methylxanthines found among the active components of cocoa.

Third-party testing is quality testing of a supplement by an organization independent of the company that makes or sells it. Each testing program sets its own checks, so what a seal covers depends on the program.

Trimethylamine N-oxide (TMAO) is a compound produced with the help of gut bacteria from nutrients such as choline in eggs and carnitine in beef. Fish and seafood also contain TMAO directly.

Triglycerides are fats built from one glycerol molecule and three fatty acids. They are the main component of body fat, and their concentration in the blood is studied as a marker of cardiovascular risk.

Vigilance most commonly means sustained attention or tonic alertness. The term covers both how awake a person is on the sleep-wake axis and how well they perform cognitively while staying alert.

VO2max, or maximal oxygen uptake, is the upper limit on how fast the body can take up and use oxygen as exercise gets harder, measured during a lab test that becomes harder until exhaustion.

Withanolides are a group of naturally occurring steroid compounds with 28 carbon atoms. Research on the active compounds in ashwagandha (Withania somnifera) has largely focused on this group.

Working memory is the ability to hold a small amount of information in mind, in a readily accessible form, and to work with it. It supports planning, comprehension, reasoning and problem-solving.