Supplement Terms Explained: A Plain-English Glossary

Supplement labels are full of terms that sound technical and are rarely explained. This glossary defines the ones that actually change what you are buying, in plain English, with a link to a fuller guide where we have one.

If you only read three entries, make them elemental magnesium, buffered and NRV. Between them, they explain most of the gap between what a label appears to say and what is in the capsule.

Jump to: Minerals and forms · Reading a label · Ingredients and capsules · Quality and testing · Vitamin D and K2 · NAC and glutathione · Sleep · Gut health

Minerals and forms

Elemental magnesium

The weight of the magnesium itself, not the compound it is bound to. 500mg of magnesium glycinate contains only about 55mg of elemental magnesium. Daily requirements and safety limits always refer to the elemental figure. Full guide to elemental magnesium.

Chelated (chelate)

A mineral bonded to one or more amino acids, which protects it in the gut and generally improves tolerance. Magnesium glycinate is a chelate. “Chelated” describes how the mineral is bound, not how much is present. Chelated magnesium explained.

Bisglycinate (glycinate)

Magnesium bonded to two molecules of the amino acid glycine. “Magnesium bisglycinate” and “magnesium glycinate” are the same compound. In practice it is about 11% elemental magnesium by weight (about 14% in theory). Bisglycinate vs glycinate.

Buffered / unbuffered

A buffered magnesium glycinate has magnesium oxide blended in to raise the elemental number on the label. Unbuffered (or non-buffered) means glycinate only. Check the ingredients list: if magnesium oxide appears, it is buffered. Buffered vs non-buffered magnesium glycinate. Our Magnesium Glycinate is unbuffered: 500mg of bisglycinate and 55mg of elemental magnesium per capsule.

Magnesium oxide

A cheap, compact form of magnesium that is about 60% elemental magnesium but poorly absorbed, with one study measuring fractional absorption around 4%. It is more likely to cause loose stools than chelated forms. Magnesium oxide vs glycinate.

Bioavailability

The share of a nutrient you swallow that is absorbed and reaches your bloodstream. A form can carry a lot of a mineral and still have low bioavailability. That is why the form matters as much as the dose. Forms of magnesium compared.

Zinc forms

Like magnesium, zinc is always bound to a partner, and the form changes both the elemental content and how well it is absorbed. Common forms include zinc picolinate, bisglycinate, citrate, gluconate and oxide. As with magnesium, compare products on the elemental zinc figure in the nutrition table. Our Vitamin D3 + K2 uses zinc citrate.

Reading a label

NRV (Nutrient Reference Value)

The reference daily amount used on UK and EU labels to show a %NRV. It is a labelling benchmark, not a personal target. For magnesium the NRV is 375mg, for vitamin D it is 5mcg and for vitamin K it is 75mcg.

RI (Reference Intake)

The term used on UK food packs for energy, fat, sugar and salt. On supplements you will mostly see NRV instead. Both are reference points for labelling, not individual recommendations.

Compound weight vs nutrient weight

Front-of-pack numbers such as “Magnesium Glycinate 1000mg” usually give the weight of the whole compound. The nutrition table should give the nutrient itself. Always compare products using the nutrition table figure.

Per capsule vs per serving

Some labels state the dose per capsule, others per daily serving of two, three or more capsules. A product can look stronger simply because its serving is larger. Divide by the number of capsules to compare like for like.

Upper limit / guidance level

The highest daily intake from supplements considered unlikely to cause harm. In the UK, the Expert Group on Vitamins and Minerals set guidance levels in 2003, such as 400mg a day of supplemental magnesium and 25mcg (1,000 IU) of vitamin D. The NHS advises that 100mcg (4,000 IU) of vitamin D a day is the maximum safe intake for adults. Vitamin D safe limits.

Food supplement

The legal category for vitamins and minerals sold in the UK as capsules, tablets or liquids. Food supplements are regulated as foods, not medicines, so they cannot claim to treat, cure or prevent any disease.

Authorised health claim

A health statement approved for use on food and supplements in Great Britain, such as “magnesium contributes to a reduction of tiredness and fatigue”. Only approved wording is allowed on packs and in advertising, and only when the product contains a meaningful amount of the nutrient.

Ingredients and capsules

Active ingredient

The ingredient you are buying the supplement for, such as magnesium bisglycinate or NAC. Everything else in the capsule is there to make it manufacturable or stable.

Excipient

Any non-active ingredient in a supplement: flow agents, bulking agents, coatings, capsule shells. Some are necessary to fill capsules consistently. Others mainly add bulk or make a pill look bigger. Clean supplements: what to avoid.

Flow agent (anti-caking agent)

A small amount of an ingredient that stops powder clumping so capsules can be filled evenly. Magnesium stearate and silicon dioxide are common. Our magnesium glycinate uses brown rice flour instead.

Bulking agent

An inert ingredient, such as microcrystalline cellulose or maltodextrin, added to fill out a capsule or tablet. It adds volume, not nutrition.

HPMC capsule

Hydroxypropyl methylcellulose, a plant-derived capsule shell used instead of gelatin. HPMC capsules are suitable for vegetarians and vegans. All Epsilon Life capsule products use HPMC shells.

Clean label

An informal term for products with short, recognisable ingredient lists and no unnecessary additives. It is not regulated, so judge it by reading the full ingredients list rather than the front of the pack.

MCT oil carrier

Medium-chain triglyceride oil, often from coconut, used as a carrier for fat-soluble vitamins such as D3 and K2. Fat-soluble vitamins are absorbed better with fat. How to improve vitamin D absorption.

Quality and testing

GMP (Good Manufacturing Practice)

A set of standards for how products are made, documented and quality-checked, covering hygiene, traceability and batch records. GMP is about the manufacturing process rather than testing each finished product.

BRCGS

A UK-founded, internationally recognised food safety certification covering hygiene, HACCP, quality systems and site standards. Major UK retailers require it of their food suppliers. Epsilon Life capsule products are made to GMP and BRCGS standards.

Certificate of Analysis (COA)

A lab report confirming what a batch contains, often potency and sometimes contaminants such as heavy metals. A COA can come from the manufacturer’s own lab or from an independent one. Ask which lab produced it and which batch it covers.

Third-party testing

Testing carried out by a lab that is independent of both the brand and the manufacturer. It is stronger evidence than an in-house certificate because the lab has no stake in the result. Check what was tested: potency only, or contaminants too. Our magnesium glycinate has been independently tested at Campden BRI for elemental magnesium content.

UKAS accreditation

The UK Accreditation Service confirms that a lab’s test methods meet recognised standards. A result from a UKAS-accredited method carries more weight than one from an unaccredited lab.

Vitamin D and K2

IU and mcg (vitamin D)

Two units for the same thing. For vitamin D, 1mcg equals 40 IU, so 10mcg is 400 IU and 100mcg is 4,000 IU. Vitamin K2 is always given in mcg. D3 and K2 dosage and ratio.

Vitamin D3 (cholecalciferol)

The form of vitamin D your skin makes from sunlight. Research suggests D3 raises blood vitamin D levels more effectively than D2 (ergocalciferol), which is why most supplements use it. The NHS advises everyone in the UK to consider 10mcg a day in autumn and winter.

MK-7 / MK-4

Two forms of vitamin K2. MK-7 stays in the blood much longer, so it suits once-daily dosing. MK-4 clears quickly and is usually given in higher, split doses. K2 MK-4 vs MK-7.

All-trans K2

MK-7 exists in “trans” and “cis” shapes, and only the all-trans shape is considered biologically active. A label stating all-trans MK-7 tells you the K2 is in its active form. Our Vitamin D3 + K2 provides 90mcg of all-trans MK-7 alongside 4,000 IU of D3.

Fat-soluble vitamin

A vitamin absorbed along with dietary fat and stored in the body: vitamins A, D, E and K. Taking them with a meal containing fat, or in an oil carrier, helps absorption.

NAC and glutathione

NAC (N-acetyl cysteine)

A stable form of the amino acid cysteine. Your body uses cysteine to make glutathione. NAC is sold as a food supplement in the UK. Our NAC+ provides 600mg per capsule. NAC is not suitable if you have cystinuria or take nitrate medications. Consult your doctor.

Glutathione

An antioxidant your cells make from three amino acids: cysteine, glycine and glutamate. Cysteine is usually the one in shortest supply. NAC vs glutathione.

Antioxidant

A substance that neutralises free radicals before they damage cells. Some are made by your body, such as glutathione. Others come from food, such as vitamin C, vitamin E and the polyphenols in fruit, vegetables, tea and coffee.

Precursor

A compound the body converts into another. NAC is a glutathione precursor: it supplies the cysteine your body needs to make its own glutathione, rather than providing glutathione directly.

Cofactor

A helper molecule, often a vitamin or mineral, that an enzyme needs in order to work. Selenium and molybdenum are both cofactors for enzymes involved in how your body uses NAC and glutathione.

Selenium

A trace mineral that the glutathione peroxidase enzymes need to work. These enzymes use glutathione to neutralise peroxides. Selenium contributes to the protection of cells from oxidative stress. Why NAC works better with selenium and molybdenum.

L-selenomethionine

An organic form of selenium, bound to the amino acid methionine. It is well absorbed and is the form used in our NAC+, which provides 25mcg of selenium per capsule.

Molybdenum

A trace mineral that acts as a cofactor for sulphite oxidase, the enzyme that converts sulphite into sulphate. Molybdenum contributes to normal sulphur amino acid metabolism, which is relevant because NAC is derived from cysteine, a sulphur-containing amino acid. NAC+ provides 45mcg per capsule. Why we added it to NAC+.

Oxidative stress

An imbalance between free radicals and the antioxidant defences that neutralise them, such as glutathione. It is a normal part of metabolism that rises with age, smoking, alcohol and illness. What is oxidative stress?

GlyNAC

A combination of glycine and NAC, the two glutathione building blocks most likely to run short. It is being studied in older adults, though the research is still at an early stage. What is GlyNAC?

Sulphur smell (NAC)

NAC capsules often smell of sulphur, a little like eggs. This comes from the sulphur-containing thiol group in the cysteine molecule. It is normal and not by itself a sign of a bad batch.

Sleep

Glycine

An amino acid with a calming role in the nervous system. In a 2007 study, 3g of glycine before bed improved subjective sleep quality. It is also the partner that magnesium is bound to in magnesium glycinate. Magnesium glycinate for sleep.

Melatonin

The hormone your brain releases in the evening to signal that it is time to sleep. In the UK, melatonin is a prescription-only medicine rather than a food supplement. Magnesium vs melatonin for sleep.

Gut health

Gut microbiome

The community of trillions of bacteria, fungi and other microorganisms living in your digestive tract, mostly in the large intestine. It helps digest fibre, produces some vitamins and interacts with your immune system. Gut health after 40.

Microbiome diversity

How many different types of microbes live in your gut, and how evenly balanced they are. Higher diversity is generally associated with better health in research, and eating a wide range of plant foods is linked to a more diverse microbiome. 30 plants a week.

Fibre

The parts of plant foods your body cannot digest. Soluble fibre dissolves in water and is fermented by gut bacteria. Insoluble fibre adds bulk and helps things move. UK adults are advised to eat 30g a day, and most eat much less. What makes a good fibre supplement.

Prebiotic

A substance, usually a type of fibre such as inulin or FOS, that feeds beneficial gut microbes selectively. Not all fibre is prebiotic. Prebiotic fibre explained and prebiotics vs probiotics.

FOS (fructo-oligosaccharides)

Short chains of fructose found in foods such as onions, garlic, bananas and chicory root, and added to many prebiotic supplements. FOS feeds beneficial bacteria, but it is also a FODMAP, so it can worsen symptoms for some people with IBS. Prebiotics and IBS.

Postbiotic

A preparation of inactivated (non-living) microorganisms or their components that benefits health, per the scientific consensus definition from 2021. The word is also used more loosely for the compounds microbes produce during fermentation, such as short-chain fatty acids.

Synbiotic

A product that combines live microorganisms with a substance those microbes can feed on, designed so the two work together. A simple example is a probiotic paired with a prebiotic fibre.

Short-chain fatty acids (SCFAs)

Compounds such as butyrate, propionate and acetate, produced when gut bacteria ferment fibre. Butyrate is the main fuel for the cells lining your colon.

Gut-brain axis

The two-way communication between your gut and your brain, through the vagus nerve, immune signals and compounds made by gut microbes. It is an active area of research, and much of the evidence so far comes from animal studies.

Gut-skin axis

The link between the gut microbiome and skin, studied in relation to conditions such as acne, eczema and rosacea. The gut-skin axis explained.

Estrobolome

The group of gut bacteria that can process oestrogen, influencing how much is reabsorbed or excreted. It is of particular interest around perimenopause and menopause. What is the estrobolome?

IBS (irritable bowel syndrome)

A common long-term condition affecting the gut, with symptoms such as bloating, cramps and changes in bowel habit. It is grouped by the main bowel pattern: IBS-C (constipation), IBS-D (diarrhoea) and IBS-M (mixed). It should be diagnosed by a GP, as other conditions can cause similar symptoms. Probiotics for IBS.

FODMAPs

Fermentable carbohydrates (oligosaccharides, disaccharides, monosaccharides and polyols) that are poorly absorbed and fermented by gut bacteria, which can trigger IBS symptoms. A low-FODMAP diet is best followed with a dietitian, as it is meant to be temporary. Natural remedies for IBS.

CFU (colony-forming units)

The number of live microorganisms in a probiotic that are able to grow. It is usually given per serving. A higher CFU count is not automatically better: the species, the format and whether the cultures survive storage all matter.

Probiotic

Live microorganisms that, when taken in adequate amounts, benefit the person who takes them (the FAO/WHO definition). Probiotics are named by genus and species, such as Lactobacillus plantarum, and sometimes by a specific strain code.

Lactobacillus (new names)

In 2020, scientists split the large Lactobacillus genus into 25 groups, so many familiar species now have new names. For example, L. rhamnosus is now Lacticaseibacillus rhamnosus and L. plantarum is now Lactiplantibacillus plantarum. Labels and studies may use either name for the same species.

Saccharomyces boulardii

A beneficial yeast rather than a bacterium, and one of the most studied probiotics. Because it is a yeast, antibacterial antibiotics do not kill it, which is why it is often researched alongside antibiotic courses. It is one of the cultures in Biome Bliss. S. boulardii explained.

Fermented (live) drink

A drink made by letting bacteria or yeasts break down sugars, which produces live cultures and organic acids. Live fermented products usually need refrigerating once opened. Biome Bliss is a fermented liquid with live cultures. What’s in Biome Bliss.

This glossary is for general information and does not constitute medical advice. If you have a medical condition or take medication, speak with your GP or pharmacist before starting a supplement.