Glossary

Adaptogen is a name for herbs said to help the body cope with stress, such as ashwagandha, rhodiola and ginseng. The term comes from Soviet research in the 1940s. It isn't a recognised scientific or legal category in the UK, so the evidence for each herb has to be judged on its own.

Read more: Ingredient Atlas

Amino acids are the building blocks of protein. Some, such as L-theanine and L-tyrosine, are also taken on their own as supplements. The L in front of a name means the form found in nature, which is the one the body uses.

Read more: L-tyrosine research

Bacosides are the main natural compounds studied in bacopa (Bacopa monnieri), a plant long used in Ayurvedic tradition. Bacopa extracts are usually standardised to a set percentage of bacosides, which differs between brands.

Read more: Bacopa research

Beta-glucans are a type of polysaccharide found in the cell walls of mushrooms and yeast, and in oats and barley. In mushroom supplements they're the main compounds checked for quality, and a beta-glucan figure is a better guide than total polysaccharides.

Read more: Best lion's mane supplements

Bioavailability is the share of what you swallow that reaches your bloodstream and can be used. It depends on the form, the dose, food and the person. Some magnesium forms are absorbed better than others, though studies comparing them are mostly small.

Read more: Magnesium glycinate vs citrate

Magnesium bisglycinate and magnesium glycinate are usually the same thing, magnesium bound to two molecules of the amino acid glycine. Bis means two. Labels use both names, so compare the elemental magnesium per capsule rather than the name.

Read more: Magnesium glycinate vs citrate

Brain fog isn't a medical diagnosis. It's an everyday name for feeling slow, forgetful or unable to focus. Common causes include poor sleep, stress, dehydration and some illnesses and medicines. If it's new or doesn't go away, it's worth speaking to a GP.

Read more: What causes brain fog

A half-life is the time the body takes to clear half of something. For caffeine it's about 5 hours in most adults, ranging from about 3 to 7. Smoking shortens it, and the contraceptive pill and pregnancy lengthen it. It's why an afternoon coffee can still be in your system at bedtime.

Read more: Caffeine calculator

With regular caffeine the body adapts, so the same amount has less effect. That's tolerance. Stopping suddenly can bring headaches, tiredness and low mood for a few days. That's withdrawal, and cutting down gradually usually avoids it.

Read more: Caffeine calculator

A case report describes what happened to one person, or a handful of people, usually written up by their doctors. Case reports are often the first sign of a rare side effect, but they can't show how common it is or prove what caused it.

A certificate of analysis is a lab report for one batch of an ingredient or product. It typically confirms what's in it, how much of the marker compounds, and that heavy metals and microbes are under set limits. Brands get them from suppliers or independent labs.

Certified organic means an ingredient was grown and processed to organic standards and checked by an approved body, such as the Soil Association in the UK. A label can say one ingredient is organic without the whole product being certified, so check which part it applies to.

A chelated mineral is bound to an amino acid or another organic molecule, rather than being a simple salt such as an oxide. Magnesium glycinate is a chelate, with magnesium bound to glycine. Chelated forms are often said to be easier on the stomach, though studies comparing forms are small.

Read more: Magnesium glycinate guide

Cortisol is a hormone made by the adrenal glands. It follows a daily rhythm, highest soon after waking and lowest around midnight, and it rises in response to stress. It helps control blood sugar, blood pressure and the body's response to inflammation. Studies often measure it in saliva or blood.

Read more: How to lower cortisol levels

In a crossover study each person tries both the treatment and the comparison in turn, usually with a break in between, called a washout. Each person acts as their own comparison, so fewer people are needed. It works best for effects that wear off quickly.

The Reference Nutrient Intake is the UK's daily amount that covers the needs of almost everyone in a group. It varies by age and sex. For magnesium it's 300 mg for men and 270 mg for women aged 19 and over, and most of it can come from food.

Read more: How much magnesium per day?

A dose-response relationship means a bigger dose gives a bigger effect, at least up to a point. Finding one strengthens the case that a substance is causing the effect. It's also why the dose on a label matters when comparing it with the doses used in studies.

Double-blind means neither the people taking part nor the researchers working with them know who is getting the treatment and who the placebo until the end. It stops expectations on either side from colouring the results.

An effect size says how big a difference is, in a way that can be compared across studies. A common rule of thumb is that 0.2 is small, 0.5 moderate and 0.8 large. A result can be statistically significant and still have a small effect size.

Elemental magnesium is the amount of magnesium itself in a supplement, without the compound it's bound to. Magnesium glycinate is about 14% magnesium by weight, so 1,000 mg of it gives about 140 mg of magnesium. UK labels list the magnesium itself with its %NRV, and that's the figure to compare.

Read more: Magnesium calculator

Our guides label each finding Strong when several good trials agree, Early when there are only one or two small trials, Mixed when trials disagree, and Moderate in between. The label describes the research, not how well something will work for you.

Read more: How we research and check our articles

Excipients are the ingredients in a capsule or tablet other than the active ones, such as fillers, flow agents and the capsule shell. They help make the product and hold it together. Most are harmless, and labels list them so you can see what else is in each capsule.

An extract ratio such as 10:1 means about 10 kg of plant went into 1 kg of extract. It describes how concentrated the extract is, but not which compounds it holds or how much of them, so a standardised percentage often tells you more.

Food supplement is the UK legal name for vitamins, minerals, herbs and similar products sold in doses such as capsules. They're regulated as food, not medicine, so they can't claim to treat, cure or prevent any illness, and their labels must carry set warnings.

The fruiting body is the part of a mushroom you see above ground. In lion's mane it's the white, shaggy part. Fruiting body extracts contain compounds such as hericenones and beta-glucans, and in the UK the fruiting body can be sold as a food.

Read more: Lion's mane research

GABA (gamma-aminobutyric acid) is the brain's main calming chemical messenger, which slows signals between nerve cells. It comes up often in research on sleep and relaxation, including studies of L-theanine and magnesium.

Ginsenosides are the main natural compounds in ginseng root, with dozens of types. Panax ginseng extracts are often standardised to a percentage of total ginsenosides. Siberian ginseng is a different plant and contains none.

Read more: Panax ginseng research

Glycine is the smallest amino acid. The body makes it, and it's in protein foods such as meat, fish and beans. In magnesium glycinate, the magnesium is bound to glycine.

Read more: Magnesium glycinate guide

Hericenones and erinacines are natural compounds found in lion's mane. Hericenones come mainly from the fruiting body and erinacines mainly from the mycelium. Both are studied in the lab for their effects on nerve cells, and evidence in people is still early.

Read more: Lion's mane research

KSM-66 is a branded ashwagandha extract made by Ixoreal Biomed in India from the root only, standardised to at least 5% withanolides. It's the extract used in many of the published ashwagandha trials, which is why labels name it.

Read more: Ashwagandha guide

L-theanine is an amino acid found mainly in tea leaves. It's studied on its own and alongside caffeine for calm and focus. Studies commonly use 100 to 400 mg a day.

Read more: L-theanine research

Melatonin is a hormone the body makes in the evening, as light fades, which helps signal that it's time to sleep. In the UK, melatonin is a prescription-only medicine, unlike in the US, so it can't be sold as a food supplement.

Read more: Melatonin in the UK

A meta-analysis pools the results of several studies on the same question into one overall estimate. Because it combines more people, it's more reliable than one small trial, as long as the studies it pools are good and similar enough to combine.

Read more: Ingredient Atlas

Mushroom supplements can be whole powder, a hot-water extract, which draws out beta-glucans, an alcohol extract for other compounds, or a dual extract that uses both. Full-spectrum usually means both fruiting body and mycelium. These names aren't regulated, so check what the label states.

Read more: Best lion's mane supplements

Mycelium is the root-like network a mushroom grows through soil, wood or its growing medium. Some supplements use mycelium grown on grain, which can carry a lot of starch. In the UK, dried lion's mane mycelium powder counts as a novel food, which needs approval before sale.

Read more: Lion's mane guide

A nootropic is a substance taken to support mental performance, such as focus, memory or calm. The word was coined in 1972 by the chemist Corneliu Giurgea. Today it covers plant extracts, amino acids and vitamins sold as food supplements, as well as prescription drugs, which are a separate thing.

Read more: What are nootropics?

The Nutrient Reference Value is a single daily figure used on UK and EU labels for each vitamin and mineral, the same for every adult. For magnesium it's 375 mg, so 150 mg shows as 40% NRV. It's a label standard, not a personal target.

Read more: Magnesium calculator

An observational study watches what people already do, such as how much coffee they drink, and looks for links with their health. It can't show that one thing causes another, because people who differ in one habit often differ in others too.

In an open-label study everyone knows what they're taking, often because there's no placebo group. These studies are useful for checking safety and doses, but expectations can shape the results, so they count for less than blinded trials.

A pilot study is a small, early study, often with a few dozen people or fewer, run to test whether a larger trial is worth doing and how to run it. Its results are a first signal, not a firm answer.

A placebo-controlled trial compares a real treatment with a dummy that looks the same, the placebo. People often feel better when they expect to, so comparing against a placebo shows how much of the change comes from the treatment itself.

Read more: Ingredient Atlas

Polysaccharides are long chains of sugar molecules. In mushroom supplements the ones of interest are beta-glucans. A label's polysaccharide figure can include starch, especially from mycelium grown on grain, so a beta-glucan figure tells you more.

Read more: Lion's mane guide

In a randomised controlled trial, people are put into groups by chance, one taking the treatment and one a placebo or other comparison. Chance spreads differences such as age and health evenly, so a difference between the groups is more likely to be down to the treatment.

Read more: Ingredient Atlas

Rosavins and salidroside are natural compounds in rhodiola root. Rosavins are found mainly in Rhodiola rosea, and extracts are often standardised to about 3% rosavins and 1% salidroside, a ratio close to the root itself.

Read more: Rhodiola research

Sleep hygiene means the daily habits and surroundings that make good sleep more likely, such as a regular wake-up time, a dark and cool bedroom, daylight in the morning and less caffeine later in the day. It's what the NHS suggests trying first for poor sleep.

Read more: How to fall asleep fast

A standardised extract is made to contain a set amount of one or more marker compounds, such as 5% withanolides in ashwagandha or 3% rosavins in rhodiola. It keeps batches consistent and makes it easier to match a product with the extracts used in studies.

Read more: Ingredient Atlas

A study in people, or human study, tests something in volunteers or patients. Lab studies use cells and animal studies use mice or rats. Those can point to how something might work, but the results often don't carry over to people, so the Atlas counts only studies in people.

Read more: Ingredient Atlas

A systematic review searches for every study on a question in a set, written-down way, judges the quality of each and sums up what they show together. Many include a meta-analysis. The Atlas lists these as pooled reviews.

Read more: Ingredient Atlas

An upper limit is the most of something you can take each day with little risk of harm. For magnesium supplements, the NHS says 400 mg a day or less is unlikely to cause harm. For caffeine, about 400 mg a day is considered safe for most adults, and 200 mg in pregnancy.

Read more: How much magnesium per day?

Most vegan capsules are made from HPMC (hydroxypropyl methylcellulose), a material made from plant cellulose, instead of gelatin, which comes from animals. They're suitable for vegetarians and vegans.

Withanolides are natural compounds found in ashwagandha, mostly in the root and leaf. Extracts are often standardised to a set percentage of withanolides, such as 5%, so one batch matches the next. The percentage describes the extract, not how well it works.

Read more: Ashwagandha research