Supplement glossary

Also called: vitamin B7, vitamin H, D-biotin

B vitamin involved in the metabolism of fats, carbohydrates and protein. It is sold for hair and nails, but deficiency is rare. Doses of several thousand µg can distort some blood tests, including thyroid and heart tests.

• NHS (UK): 0.9 mg (900 µg) or less a day from supplements is unlikely to cause harm
• NRV: 50 µg a day
• EFSA upper level: not set
• Claims (UK and EU): maintenance of normal hair, skin and mucous membranes, energy-yielding metabolism, nervous system, psychological function
• Tell your doctor or lab you take biotin before a blood test

More: Biotin Biotin for hair loss: does it work, and what to check first

Sources: NHS — B vitamins and folic acidNIH ODS — Biotin

Also called: folic acid, vitamin B9, 5-MTHF, L-methylfolate

B vitamin needed for cell division and blood formation. Folic acid is the synthetic form used in most supplements. Taking it before and in early pregnancy lowers the risk of neural tube defects in the baby.

• NHS (UK): 400 µg folic acid a day before pregnancy and until week 12; 1 mg or less a day from supplements is unlikely to cause harm
• NRV: 200 µg a day
• EFSA upper level: 1,000 µg a day of folic acid from supplements and fortified foods (folate from food not counted)
• Before and in early pregnancy: 400 µg folic acid a day is the usual recommendation
• Claims (UK and EU): blood formation, cell division, maternal tissue growth in pregnancy, immune system, psychological function, reduction of tiredness and fatigue

More: Multivitamins Are multivitamins worth it? What the big studies found

Sources: NHS — B vitamins and folic acidNIH ODS — FolateEFSA — Summary of tolerable upper intake levels (2024)

Also called: retinol, retinyl acetate, retinyl palmitate, beta-carotene

Fat-soluble vitamin needed for vision, skin and the immune system. Supplements contain preformed vitamin A (retinol) or beta-carotene, which the body converts into vitamin A as needed.

• NHS (UK): no more than 1.5 mg (1,500 µg) a day from food and supplements combined; avoid vitamin A supplements, including fish liver oil, in pregnancy
• NRV: 800 µg a day
• EFSA upper level: 3,000 µg a day of preformed vitamin A (not beta-carotene)
• Claims (UK and EU): normal vision, skin, mucous membranes, immune system and iron metabolism
• Avoid high-dose vitamin A in pregnancy; smokers should avoid beta-carotene supplements

More: Are multivitamins worth it? What the big studies found

Sources: NHS — Vitamin ANIH ODS — Vitamin A and carotenoidsEFSA — Summary of tolerable upper intake levels (2024)

Also called: thiamine, thiamine hydrochloride, thiamine mononitrate

B vitamin the body needs to turn carbohydrates into energy and for nerve function. A varied diet usually covers it; heavy alcohol use is the main cause of deficiency.

• NRV: 1.1 mg a day
• EFSA upper level: not set
• Claims (UK and EU): energy-yielding metabolism, nervous system, psychological function, heart function

More: Multivitamins

Source: NIH ODS — Thiamin

Also called: riboflavin, riboflavin-5'-phosphate

B vitamin involved in energy metabolism and in activating other B vitamins. Higher doses turn urine bright yellow, which is harmless.

• NRV: 1.4 mg a day
• EFSA upper level: not set
• Claims (UK and EU): energy-yielding metabolism, reduction of tiredness and fatigue, normal vision, skin and red blood cells, protection of cells from oxidative stress

More: Multivitamins

Source: NIH ODS — Riboflavin

Also called: nicotinamide, niacinamide, nicotinic acid

B vitamin used in energy metabolism. Labels list it as nicotinamide (niacinamide) or nicotinic acid; nicotinic acid causes skin flushing at much lower doses and has a far lower upper level.

• NRV: 16 mg a day
• EFSA upper levels: 10 mg a day as nicotinic acid, 900 mg a day as nicotinamide
• Claims (UK and EU): energy-yielding metabolism, nervous system, psychological function, skin, reduction of tiredness and fatigue

More: Multivitamins

Sources: NIH ODS — NiacinEFSA — Summary of tolerable upper intake levels (2024)

Also called: calcium D-pantothenate, pantethine

B vitamin present in almost all foods and needed to make coenzyme A, a key molecule in energy metabolism. Deficiency is very rare.

• NRV: 6 mg a day
• EFSA upper level: not set
• Claims (UK and EU): energy-yielding metabolism, normal mental performance, synthesis of steroid hormones, vitamin D and some neurotransmitters, reduction of tiredness and fatigue

More: Multivitamins

Source: NIH ODS — Pantothenic acid

Also called: pyridoxine hydrochloride, pyridoxal-5'-phosphate (P-5-P)

B vitamin involved in protein metabolism, red blood cell formation and the nervous system. It is often added to magnesium products. Taking too much for a long time can damage nerves, so add up the B6 from all your supplements.

• NHS (UK): no more than 10 mg a day from supplements unless a doctor advises it
• NRV: 1.4 mg a day
• EFSA upper level: 12 mg a day from all sources
• Claims (UK and EU): energy-yielding metabolism, nervous system, psychological function, immune system, red blood cell formation, reduction of tiredness and fatigue, regulation of hormonal activity

More: Multivitamins

Sources: NHS — B vitamins and folic acidNIH ODS — Vitamin B6EFSA — Summary of tolerable upper intake levels (2024)

Also called: cobalamin, cyanocobalamin, methylcobalamin, hydroxocobalamin

Needed for red blood cells and the nervous system. It occurs almost only in animal foods, so vegans need a supplement or fortified foods. The body absorbs only a small share of large doses: about 1.3 % of 1,000 µg.

• NHS (UK): adults need about 1.5 µg a day; 2 mg or less a day from supplements is unlikely to cause harm
• NRV: 2.5 µg a day
• EFSA adequate intake: 4 µg a day
• EFSA upper level: not set
• Claims (UK and EU): reduction of tiredness and fatigue, energy-yielding metabolism, red blood cell formation, nervous system, psychological function, immune system

More: Vitamin B12 Vitamin B12 supplements: who needs one and how much

Sources: NHS — B vitamins and folic acidNIH ODS — Vitamin B12

Also called: ascorbic acid, sodium ascorbate, calcium ascorbate

Water-soluble vitamin needed to form collagen and for the immune system; it also increases iron absorption from food. Doses of a gram or more can upset the stomach.

• NHS (UK): adults need 40 mg a day; less than 1,000 mg a day from supplements is unlikely to cause harm
• NRV: 80 mg a day
• EFSA upper level: not set
• Germany (BfR guidance): 250 mg per daily dose
• Claims (UK and EU): immune system, collagen formation for blood vessels, bones, cartilage, gums, skin and teeth, reduction of tiredness and fatigue, iron absorption, protection of cells from oxidative stress

More: Vitamin C Zinc and vitamin C for colds: what actually works

Sources: NHS — Vitamin CNIH ODS — Vitamin C

Also called: cholecalciferol (vitamin D3), ergocalciferol (vitamin D2)

Fat-soluble vitamin that the skin makes in sunlight; in winter, much of Europe gets too little UVB for that. Needed for calcium absorption, bones, muscles and the immune system. Most supplements contain vitamin D3.

• NHS (UK): 10 µg (400 IU) a day, as a supplement in autumn and winter for everyone; no more than 100 µg a day for adults
• NRV on labels: 5 µg (200 IU) a day
• EFSA adequate intake: 15 µg (600 IU) a day
• EFSA upper level: 100 µg (4,000 IU) a day from all sources
• Germany (BfR guidance): 20 µg (800 IU) per daily dose
• Claims (UK and EU): immune system, bones, teeth, muscle function, calcium absorption

More: Vitamin D Vitamin D in winter: UK advice, dose and the safe maximum

Sources: NHS — Vitamin DNIH ODS — Vitamin DEFSA (2023) — Tolerable upper intake level for vitamin DBfR — Recommended maximum levels for vitamins and minerals in food supplements

Also called: menaquinone, MK-7, MK-4; vitamin K1 = phylloquinone

Form of vitamin K, which is needed for blood clotting and bone metabolism. It is often combined with vitamin D3. If you take vitamin K antagonist blood thinners (warfarin, acenocoumarol/Sintrom, phenprocoumon/Marcumar), talk to your doctor first.

• NRV (vitamin K): 75 µg a day
• EFSA upper level: not set
• Claims (UK and EU, vitamin K): normal blood clotting, maintenance of normal bones

More: Vitamin D Vitamin D3 with K2: do you really need the K2?

Source: NIH ODS — Vitamin K

Also called: ferrous bisglycinate, ferrous sulphate, ferrous fumarate, ferrous gluconate

Mineral needed to make haemoglobin and carry oxygen in the blood. A supplement only helps if your iron stores are low, so have your ferritin checked first; too much iron is harmful and often causes constipation or nausea.

• NHS (UK): adults need 8.7 mg a day (14.8 mg for women aged 19–49); 17 mg or less a day from supplements is unlikely to cause harm
• NRV: 14 mg a day
• EFSA safe level of total intake: 40 mg a day
• Germany (BfR guidance): 6 mg per daily dose
• Claims (UK and EU): reduction of tiredness and fatigue, red blood cells and haemoglobin, oxygen transport, cognitive function, immune system

More: Iron Iron and tiredness: when an iron supplement actually helps

Sources: NHS — IronNIH ODS — IronEFSA — Summary of tolerable upper intake levels (2024)

Also called: magnesium citrate, bisglycinate, oxide, malate, chloride

Mineral involved in muscle and nerve function and in energy metabolism. On labels, compare the elemental magnesium per daily dose, not the weight of the compound.

• NHS (UK): adults need 300 mg (men) or 270 mg (women) a day; 400 mg or less a day from supplements is unlikely to cause harm
• NRV: 375 mg a day
• EFSA upper level from supplements: 250 mg a day (magnesium from food not counted)
• Germany (BfR guidance): 250 mg a day, split into at least two doses
• Claims (UK and EU): reduction of tiredness and fatigue, muscle function, nervous system, psychological function, electrolyte balance, bones and teeth. No authorised sleep claim.

More: Magnesium Magnesium forms compared: which one to buy in the UK and EU

Sources: NHS — Others (magnesium, selenium, zinc)NIH ODS — MagnesiumEFSA — Summary of tolerable upper intake levels (2024)

Also called: L-selenomethionine, sodium selenite, selenium yeast

Trace mineral needed for the thyroid, the immune system and antioxidant enzymes. The gap between enough and too much is small, so add up the selenium from multivitamins, hair products and Brazil nuts.

• NHS (UK): adults need 75 µg (men) or 60 µg (women) a day; 350 µg or less a day from supplements is unlikely to cause harm
• NRV: 55 µg a day
• EFSA upper level: 255 µg a day
• Claims (UK and EU): thyroid function, immune system, hair and nails, protection of cells from oxidative stress, spermatogenesis

Sources: NHS — Others (magnesium, selenium, zinc)NIH ODS — SeleniumEFSA — Summary of tolerable upper intake levels (2024)

Also called: zinc gluconate, citrate, bisglycinate, picolinate, oxide

Trace mineral needed for the immune system, skin, hair, nails and fertility. Taking more than the upper level for a long time can cause copper deficiency.

• NHS (UK): adults need 9.5 mg (men) or 7 mg (women) a day; no more than 25 mg a day from supplements unless a doctor advises it
• NRV: 10 mg a day
• EFSA upper level: 25 mg a day from food and supplements together
• Germany (BfR guidance): 6.5 mg per daily dose
• Claims (UK and EU): immune system, skin, hair, nails, bones, fertility and reproduction, normal testosterone levels, cognitive function, vision

More: Zinc Zinc and vitamin C for colds: what actually works

Sources: NHS — Others (magnesium, selenium, zinc)NIH ODS — ZincEFSA — Summary of tolerable upper intake levels (2024)

Also called: CoQ10, ubiquinone, ubiquinol

Substance the body makes itself and uses for energy production in cells. Statins lower its level in the blood, but the evidence does not show that supplements prevent statin-related muscle pain.

• No authorised claim (UK or EU): EFSA assessed claims for energy, heart and blood pressure
• Typical supplement dose: 100–200 mg a day
• May interact with warfarin

More: Coenzyme Q10 CoQ10 and statins: does it help with muscle pain?

Sources: NIH NCCIH — Coenzyme Q10EFSA (2010) — Health claims related to coenzyme Q10

Also called: omega-3 DHA

Long-chain omega-3 fatty acid and a building block of the brain and the retina. Algae oil is the vegan source.

• Claims (UK and EU): maintenance of normal brain function and normal vision from 250 mg DHA a day; heart function together with EPA

More: Omega-3 Omega-3: fish oil vs algae oil — which to choose

Source: NIH ODS — Omega-3 fatty acids

Also called: omega-3 EPA

Long-chain omega-3 fatty acid from fish, krill and some algae oils. Its EU claims only apply together with DHA.

• Claims (UK and EU) with DHA: normal heart function from 250 mg EPA + DHA a day; normal blood triglycerides from 2 g and normal blood pressure from 3 g a day
• BfR: high doses can raise the risk of atrial fibrillation in people with heart disease

More: Omega-3 Omega-3: fish oil vs algae oil — which to choose

Sources: NIH ODS — Omega-3 fatty acidsBfR — Omega-3 preparations can increase the risk of atrial fibrillation in heart patients

Also called: EPA, DHA, ALA; fish oil, algae oil, krill oil

Family of polyunsaturated fats. The authorised claims are for EPA and DHA, the long-chain forms in fish, krill and algae oil; the body converts only a small part of ALA from flax or walnuts into them. Compare EPA + DHA per daily dose, not the amount of fish oil per capsule.

• NHS (UK): at least 2 portions of fish a week, 1 of them oily
• EFSA: up to 5 g EPA + DHA a day from supplements raises no safety concern
• A typical 1,000 mg fish-oil capsule contains about 300 mg EPA + DHA
• Claims (UK and EU): heart function (250 mg EPA + DHA a day), brain function and vision (250 mg DHA a day)

More: Omega-3 Omega-3: fish oil vs algae oil — which to choose

Sources: NHS — Fish and shellfishNIH ODS — Omega-3 fatty acidsEFSA (2012) — Safety of long-chain omega-3 fatty acids

Also called: 5-hydroxytryptophan, Griffonia simplicifolia seed extract

Precursor the body uses to make serotonin, extracted from the seeds of the African Griffonia plant. Good-quality evidence for sleep or mood is limited.

• No authorised claim (UK or EU)
• Do not combine with antidepressants or other drugs that raise serotonin (risk of serotonin syndrome)

More: Sleep

Source: Hinz M et al. 5-HTP efficacy and contraindications (2012)

Also called: chondroitin sulphate

Component of cartilage, extracted from cattle, pig, chicken or fish cartilage. Usually combined with glucosamine.

• No authorised claim (UK or EU)
• Dose used in trials: 800–1,200 mg a day

More: Joints Glucosamine and chondroitin: do they work for knee pain?

Source: NIH NCCIH — Glucosamine and chondroitin for osteoarthritis

Also called: hydrolysed collagen, collagen peptides, collagen hydrolysate; types I, II, III

Main structural protein of skin, tendons, cartilage and bone. Supplements contain collagen broken down into small peptides (hydrolysed), from cattle, pigs, fish or chicken.

• No authorised claim (UK or EU); a joint claim for collagen hydrolysate was refused in 2012
• Dose used in studies: 2.5–10 g a day
• Products often add vitamin C, which carries the authorised collagen-formation claim

More: Collagen Collagen with magnesium or hyaluronic acid: which to choose?

Source: Commission Regulation (EU) No 379/2012 — refused health claims, including collagen hydrolysate

Also called: creatine monohydrate, Creapure

Compound made from amino acids and stored in muscle, where it supplies quick energy for short, intense efforts. Monohydrate is the form used in almost all studies; it is about 88 % creatine.

• Great Britain rejected a claim that creatine improves cognitive function (2024)
• Claim (UK and EU): increases performance in repeated short bursts of high-intensity exercise (3 g creatine a day)
• Claim (UK and EU), adults over 55: enhances the effect of resistance training on muscle strength (3 g a day)
• Usual dose: 3–5 g a day

More: Creatine Creatine monohydrate: dose, Creapure and what the law allows

Sources: UKNHCC (2024) — creatine and cognitive functionNIH ODS — Dietary supplements for exercise and athletic performanceCommission Implementing Regulation (EU) 2017/672 — creatine and resistance training in adults over 55

Also called: glucosamine sulphate, glucosamine hydrochloride

Building block of cartilage, usually made from shellfish shells. It is sold for joints, but trial results for knee pain are mixed.

• UK (NICE): doctors should not offer glucosamine for osteoarthritis; no strong evidence of benefit
• No authorised claim (UK or EU): EFSA found no cause-and-effect relationship for joint claims
• Dose used in trials: 1,500 mg a day
• Often made from shellfish (allergy); high doses may interact with warfarin

More: Joints Glucosamine and chondroitin: do they work for knee pain?

Sources: NICE NG226 — Osteoarthritis (1.4.6)NIH NCCIH — Glucosamine and chondroitin for osteoarthritisEFSA (2009) — Glucosamine and maintenance of joints

Also called: sodium hyaluronate

Water-binding substance found in skin and joint fluid. Most supplement hyaluronic acid is made by bacterial fermentation; some comes from rooster combs. A 2025 meta-analysis of 7 small trials found better skin hydration, elasticity and wrinkle depth.

• No authorised claim (UK or EU)

More: Hyaluronic acid Collagen with magnesium or hyaluronic acid: which to choose?

Sources: Amin P et al. Oral hyaluronic acid supplement: skin hydration, elasticity and wrinkle depth (meta-analysis, 2025)European Commission — EU Register of nutrition and health claims

Also called: theanine, Suntheanine

Amino acid found in tea leaves. Small trials at about 200 mg suggest a calming effect without drowsiness, often combined with caffeine.

• No authorised claim (UK or EU): EFSA (2011) found claims on cognition, stress and sleep not substantiated

More: Sleep

Source: EFSA (2011) — Health claims related to L-theanine (cognition, stress, sleep)

Also called: N-acetyl-5-methoxytryptamine

Hormone the body releases in the evening to signal night-time. Supplements can shorten the time to fall asleep a little and ease jet lag. In several countries higher doses are legally a medicine.

• UK: prescription-only medicine; it cannot legally be sold as a food supplement
• EU claims (not usable in the UK): reduces the time taken to fall asleep (1 mg close to bedtime); eases jet lag (0.5 mg on travel days)
• Spain: below 2 mg a day as a supplement; 2 mg or more is a medicine
• Not for pregnancy, breastfeeding or children

More: Melatonin Melatonin in the UK and Europe: dose, legal status, claims

Sources: MHRA (2025) — melatonin is a prescription-only medicineNIH NCCIH — Melatonin: what you need to knowAEMPS — Withdrawal of a 3 mg melatonin supplement (medicine from 2 mg)

Also called: methylsulphonylmethane, organic sulphur

Sulphur compound sold for joints, often together with glucosamine. The evidence comes from a few small trials.

• No authorised claim (UK or EU): EFSA assessed claims on collagen formation, hair, nails and joints

More: Joints Glucosamine and chondroitin: do they work for knee pain?

Sources: NIH NCCIH — DMSO and MSM for osteoarthritisEFSA (2010) — Health claims related to methylsulphonylmethane (MSM)

Also called: live cultures, Lactobacillus, Bifidobacterium, Saccharomyces boulardii

Live microorganisms, mostly bacteria and some yeasts. Effects depend on the strain: some strains help with antibiotic-related diarrhoea, many have no proven effect. Compare products by strain name and CFU per daily dose.

• UK: the Department of Health treats the word "probiotic" itself as a health claim, so it should not appear on labels
• No authorised claim (UK or EU) for any strain

More: Gut & digestion

Sources: ASA — Food: probiotic claimsNIH NCCIH — Probiotics: what you need to knowHempel S et al. Probiotics for antibiotic-associated diarrhea. JAMA, 2012

Also called: ispaghula, Plantago ovata

Husk of Plantago ovata seeds: a soluble fibre that absorbs water and forms a gel, adding bulk to stools. It is used for both constipation and loose stools; always take it with plenty of water.

• NHS (UK): adults should aim for 30 g of fibre a day
• EFSA adequate fibre intake for adults: 25 g a day
• Also sold as a medicine for constipation

More: Gut & digestion

Sources: NHS — How to get more fibre into your dietMedlinePlus — PsylliumEFSA — Dietary reference values (fibre)

Also called: Cynara scolymus, artichoke extract

Leaf extract traditionally used for indigestion and bloating; the European Medicines Agency has assessed it as a traditional herbal medicine. Liver "detox" effects are unproven.

More: Gut & digestion

Source: EMA — Cynarae folium (herbal medicinal product)

Also called: Withania somnifera, winter cherry, KSM-66, Sensoril

Root (sometimes leaf) extract of an Ayurvedic plant, sold for stress and sleep. Trials use 300–600 mg of extract a day for 8–12 weeks. Rare cases of liver injury have been reported; Denmark banned it in supplements and the Netherlands has proposed banning the leaf.

• UK (FSA): under safety review; pregnant women and people with liver conditions are advised to avoid it
• Germany (BfR, 2024): no safe daily amount could be derived
• Not in pregnancy or with thyroid conditions

More: Ashwagandha Is ashwagandha legal in the UK and EU? By country (2026)

Sources: Which? — Ashwagandha: stress buster or health risk? (FSA advice)NIH ODS — AshwagandhaBfR — Ashwagandha preparations with possible health risks (2024)

Also called: Eschscholzia californica

Herb traditionally used for mild nervous tension and sleep, usually in blends. The European Medicines Agency has assessed it as a traditional herbal medicine.

More: Sleep

Source: EMA — Eschscholziae herba (herbal medicinal product)

Also called: Matricaria chamomilla, German chamomile

Flower used as tea and extract for relaxation and digestion. Evidence for sleep is weak. People allergic to daisy-family plants can react to it.

More: Sleep

Source: NIH NCCIH — Chamomile

Also called: Taraxacum officinale

Root and leaf traditionally used for digestion and as a mild diuretic. There is little clinical evidence.

Source: NIH NCCIH — Dandelion

Also called: Lavandula angustifolia, lavender oil

Flower and essential oil traditionally used for calm and sleep. The trial evidence is for a specific standardised lavender oil in capsules (80 mg a day), not for small amounts in blends or teas.

More: Sleep

Source: NIH NCCIH — Lavender

Also called: Melissa officinalis, melissa

Leaf traditionally used for calm and sleep and for mild digestive complaints; the European Medicines Agency has assessed it as a traditional herbal medicine. Trials are small and often combine it with valerian.

More: Sleep

Source: EMA — Melissae folium (herbal medicinal product)

Also called: Silybum marianum, silymarin

Seed extract widely sold for the liver; silymarin is its mix of active compounds. Human trials in liver disease give inconsistent results.

• People allergic to daisy-family plants can react to it

Source: NIH NCCIH — Milk thistle

Also called: Passiflora incarnata

Flowering plant traditionally used for nervousness and sleep, often in blends with valerian or lemon balm. There is little trial data.

More: Sleep

Source: NIH NCCIH — Passionflower

Also called: Rhodiola rosea, roseroot, golden root

Root extract of a plant from cold regions, traditionally used against fatigue and stress. Several trials suggest less stress-related fatigue, but the studies are small.

• Avoid with bipolar disorder and in pregnancy

Source: NIH NCCIH — Rhodiola

Also called: Curcuma longa, curcuminoids, piperine

Curcumin is the yellow compound in turmeric root. It is poorly absorbed, so many products add piperine or use special formulations, which also raise exposure. Rare cases of liver injury have been reported; Italy now requires a warning on the label.

• UK (Committee on Toxicity, 2024): reasonable evidence of a link between turmeric supplements and rare liver injury
• EFSA acceptable daily intake for curcumin (as food colour E 100): 3 mg per kg body weight, about 210 mg a day at 70 kg
• Avoid with gallstones or blood thinners

More: Turmeric & curcumin Turmeric supplements and your liver: what regulators say

Sources: COT (2024) — Turmeric and curcumin supplementsNIH NCCIH — TurmericEFSA (2010) — Re-evaluation of curcumin (E 100) as a food additive

Also called: Valeriana officinalis, valerian root

Root traditionally used for sleep and nervous tension, often combined with hops or lemon balm. Trial results are mixed, with at best a small effect after 2–4 weeks.

More: Sleep

Source: NIH NCCIH — Valerian

Also called: glycinate, chelate, e.g. magnesium bisglycinate, iron bisglycinate (Ferrochel)

A mineral bound to two molecules of the amino acid glycine. Often chosen by people with a sensitive stomach, but it is heavy: 1,000 mg of magnesium bisglycinate contains only about 140 mg of magnesium.

More: Magnesium Magnesium forms compared: which one to buy in the UK and EU

Source: NIH ODS — Magnesium (forms and absorption)

Also called: vitamin D3, vitamin D2

Cholecalciferol is vitamin D3, the form the skin makes. It usually comes from lanolin (sheep's wool) or, in vegan products, from lichen. Ergocalciferol (D2) comes from fungi and yeast and raises blood levels less than D3.

More: Vitamin D Vitamin D in winter: UK advice, dose and the safe maximum

Sources: Tripkovic L et al. Comparison of vitamin D2 and vitamin D3 supplementation. Am J Clin Nutr, 2012NIH ODS — Vitamin D

Also called: e.g. magnesium citrate, zinc citrate, calcium citrate

A mineral bound to citric acid. It dissolves well in water, and the NIH notes that well-dissolving forms of magnesium are absorbed better than poorly soluble ones such as oxide. A common middle ground between price and absorption.

More: Magnesium Magnesium forms compared: which one to buy in the UK and EU

Source: NIH ODS — Magnesium (forms and absorption)

Also called: branded creatine monohydrate

Brand of creatine monohydrate made in Germany by AlzChem. Chemically it is the same monohydrate as generic creatine; the extra price buys a known manufacturer and purity testing.

More: Creatine HSN vs Myprotein vs Prozis: how to compare them properly

Source: HSN — Creatine Excell 100% Creapure (origin)

Also called: vitamin B12 forms, hydroxocobalamin, adenosylcobalamin

Forms of vitamin B12. Cyanocobalamin is the most studied and most stable. Methylcobalamin is often sold as the "active" form, but the NIH says there is no evidence that it works better.

More: Vitamin B12 Vitamin B12 supplements: who needs one and how much

Source: NIH ODS — Vitamin B12

Also called: L-methylfolate, 5-methyltetrahydrofolate, Quatrefolic, Metafolin

The form of folate that circulates in the blood; folic acid is the synthetic form the body has to convert first. The pregnancy studies behind the official folic acid advice used folic acid.

More: Multivitamins

Source: NIH ODS — Folate

Also called: vitamin K2 MK-7

Form of vitamin K2 that stays in the blood much longer than vitamin K1 or MK-4. Most vitamin D3 + K2 products use it.

More: Vitamin D Vitamin D3 with K2: do you really need the K2?

Source: NIH ODS — Vitamin K

Also called: e.g. magnesium oxide, zinc oxide

A mineral bound to oxygen. It packs a lot of mineral into a small tablet (magnesium oxide is about 60 % magnesium) but dissolves poorly, so less of it is absorbed.

More: Magnesium Magnesium forms compared: which one to buy in the UK and EU

Source: NIH ODS — Magnesium (forms and absorption)

Also called: black pepper extract, BioPerine

Compound from black pepper added to turmeric products to increase how much curcumin is absorbed. It can also change how the body breaks down some medicines, so check with a pharmacist if you take regular medication.

More: Turmeric & curcumin Turmeric supplements and your liver: what regulators say

Source: NIH NCCIH — Turmeric

Also called: e.g. "5 % withanolides", KSM-66, Sensoril

A plant extract adjusted to contain a fixed share of a marker compound. Branded extracts such as KSM-66 or Sensoril (ashwagandha) were tested in specific trials, so those results don't automatically apply to other extracts or to plain powdered root.

More: Ashwagandha Is ashwagandha legal in the UK and EU? By country (2026)

Source: NIH ODS — Ashwagandha (extracts used in trials)

Also called: dietary reference values (DRVs)

Daily intake references for healthy people. In the UK the NHS uses UK reference values (for example 10 µg of vitamin D, 40 mg of vitamin C); EFSA sets its own for the EU (15 µg and 95–110 mg). Both differ from the NRV on labels: for vitamin D the NRV is 5 µg.

Sources: NHS — Vitamins and mineralsEFSA — Dietary reference values

Also called: Spanish Agency for Food Safety and Nutrition

Spain's food safety agency. Supplements sold in Spain are notified to the authorities before sale, and AESAN publishes a searchable list of notified products. A notification is not an approval or a quality check.

Source: AESAN — Food supplements

Also called: German Federal Institute for Risk Assessment (Bundesinstitut für Risikobewertung)

Germany's scientific agency for food and product risks. It publishes the recommended maximum amounts of vitamins and minerals per daily dose that German supplements are measured against, and risk assessments of ingredients such as ashwagandha.

Source: BfR — Recommended maximum levels for vitamins and minerals in food supplements

Also called: absorption

The share of a nutrient that is absorbed and available to the body. It depends on the form, the dose (the share absorbed falls as doses rise, as with vitamin B12) and what you take it with (vitamin C increases iron absorption).

Sources: NIH ODS — Vitamin B12 (absorption by dose)NIH ODS — Iron (absorption)

Also called: billion CFU

The number of live microorganisms in a probiotic, usually in billions per daily dose. It only means something together with the strain name, and only if the amount is guaranteed until the best-before date rather than at manufacture.

More: Gut & digestion

Source: NIH NCCIH — Probiotics: what you need to know

Also called: on-hold claims, botanical claims

Health claims for plant ingredients, such as ashwagandha, turmeric or valerian, have been "on hold" at EU level since 2010, neither authorised nor rejected, and Great Britain kept the same on-hold list after Brexit. Some countries tolerate them on labels under transitional rules. NutriMetrics treats them as not authorised.

More: Approved supplement health claims (UK and EU): full table

Source: European Commission — Nutrition and health claims (overview and legislation)

Also called: European Food Safety Authority

The EU's food safety agency in Parma. It assesses the science behind health claims, novel foods and safe intake levels; the European Commission and the member states then decide the law.

Source: EFSA — Dietary reference values

Also called: elemental magnesium, elemental iron

The weight of the mineral itself rather than the whole compound. 1,000 mg of magnesium bisglycinate contains only about 140 mg of elemental magnesium. The nutrition table gives the amount of the nutrient per daily dose; the front of the pack often shows the compound weight.

More: Magnesium Magnesium forms compared: which one to buy in the UK and EU

Source: Directive 2002/46/EC on food supplements (labelling, Article 8)

Also called: dietary supplement

Legally a food in concentrated form (capsules, tablets, powders, drops) that supplements the normal diet. In England the rules are in the Food Supplements (England) Regulations 2003, with equivalents in Scotland, Wales and Northern Ireland; in the EU, Directive 2002/46/EC. It needs no approval before sale: in the UK there is no product notification at all, while Spain (AESAN) and Germany (BVL) require one. It may not claim to prevent, treat or cure a disease.

More: Reading a supplement label (UK & EU): NRV, doses, red flags

Sources: The Food Supplements (England) Regulations 2003Directive 2002/46/EC on food supplementsAESAN — Food supplements

Also called: authorised health claim, EU claim

Any statement that a food or ingredient benefits health, such as "contributes to the normal function of the immune system". In Great Britain only claims on the GB nutrition and health claims register may be used; in Northern Ireland and the EU, only those on the EU Register. The two lists started out identical in 2021 and still match for vitamins and minerals. Claims must use wording close to the approved text, and the product must contain enough of the nutrient.

More: Approved supplement health claims (UK and EU): full table

Sources: DHSC — Great Britain nutrition and health claims (NHC) registerRegulation (EC) No 1924/2006 on nutrition and health claimsEuropean Commission — EU Register of nutrition and health claims

Also called: IE, UI

Older unit of biological activity still printed for vitamin D (and sometimes A and E). For vitamin D, 1 µg = 40 IU, so 20 µg = 800 IU.

More: Vitamin D Vitamin D in winter: UK advice, dose and the safe maximum

Source: NIH ODS — Vitamin D

Also called: national maximum levels, BfR maximum level recommendations (Höchstmengenempfehlungen)

Neither the UK nor the EU has set binding maximum amounts of vitamins and minerals per daily dose in supplements. In the UK, the NHS publishes amounts from supplements that are unlikely to cause harm (for example 100 µg vitamin D, 25 mg zinc). In the EU each country decides: some have binding limits; Germany's BfR publishes recommended maximums (for example 20 µg vitamin D and 250 mg magnesium); Spain has no national maximum for most vitamins and minerals.

• EU: the Commission's plan lists adoption of common maximums for the first quarter of 2028; in October 2026 it said no public consultation is planned for 2026

More: Supplement maximum levels: UK and Europe by country (2026)

Sources: NHS — Vitamins and mineralsDirective 2002/46/EC on food supplements (Article 5)BfR — Recommended maximum levels for vitamins and minerals in food supplementsHBW Insight — Commission says no 2026 consultation planned on EU supplement limits (22 Oct 2026)

Also called: mutual recognition principle

EU principle that a product lawfully sold in one member state can in principle also be sold in another, even if it does not meet that country's own rules, unless the authorities justify a restriction (for example on health grounds). It explains why some supplements on Spanish or German shelves exceed national guidance. It does not apply between the EU and Great Britain.

More: Supplement maximum levels: UK and Europe by country (2026)

Source: Regulation (EU) 2019/515 on mutual recognition of goods

Also called: novel food authorisation

A food or ingredient that was not consumed to a significant degree before 15 May 1997. It needs authorisation before it can be sold: from the Food Standards Agency (and Food Standards Scotland) for Great Britain, from the EU for Northern Ireland and the EU. Authorisations often come with conditions such as a maximum daily amount or a label warning.

Sources: FSA — Novel foods authorisation guidanceRegulation (EU) 2015/2283 on novel foods

Also called: % NRV, formerly RDA

The reference amount of a vitamin or mineral per day used on UK and EU labels, set in Regulation 1169/2011 (kept in UK law after Brexit). "% NRV" shows how much of that amount one daily dose gives. It is a labelling benchmark, not a personal requirement and not a safety limit.

• A nutrient may use its authorised claims from 15 % of the NRV per daily dose

More: Multivitamins Reading a supplement label (UK & EU): NRV, doses, red flags

Source: Regulation (EU) No 1169/2011 on food information to consumers, Annex XIII

Also called: placebo-controlled, double-blind

A study in which participants are assigned by chance to the supplement or a placebo, ideally without anyone knowing who gets what (double-blind). The most reliable single study design for showing that a supplement causes an effect.

Also called: daily portion, serving

The amount the label tells you to take per day. All amounts and % NRV on a supplement label refer to this daily dose, and the label must warn not to exceed it. Compare products per daily dose, not per capsule.

More: Reading a supplement label (UK & EU): NRV, doses, red flags

Source: Directive 2002/46/EC on food supplements (labelling, Articles 6 and 8)

Also called: Cochrane review

A systematic review collects all studies on a question using a fixed, published method; a meta-analysis then combines their results statistically. Cochrane reviews are a well-known example. NutriMetrics prefers this level of evidence over single studies.

Also called: upper level, safe upper level, safe level of intake

The highest daily intake from all sources that EFSA considers unlikely to harm healthy people over the long term. It is a ceiling, not a target. Where the data are too limited for a UL, EFSA sometimes sets a "safe level of intake" instead (for example 40 mg a day for iron). In the UK, the NHS gives its own figures for supplements, based on the 2003 Expert Group on Vitamins and Minerals (for example 25 mg of zinc, 400 mg of magnesium).

More: Supplement maximum levels: UK and Europe by country (2026)

Sources: NHS — Vitamins and mineralsEFSA — Summary of tolerable upper intake levels (2024)

Also called: traditional herbal medicinal product, THMP

A registered medicine whose approval rests on long-standing use rather than clinical trials, under Directive 2004/24/EC; in the UK, the MHRA's Traditional Herbal Registration (THR) scheme, shown by a THR mark on the pack. The same plant can be sold as a supplement or as a medicine; only the medicine may state what it is used for, such as "to aid sleep".

Source: Directive 2004/24/EC on traditional herbal medicinal products

Also called: microgram (mcg), milligram, gram

1 g = 1,000 mg and 1 mg = 1,000 µg (also written mcg). Vitamins B12, D, K, biotin, folate, selenium and iodine are counted in µg; magnesium, iron, zinc and vitamin C in mg. Mixing them up means a 1,000-fold error.

More: Reading a supplement label (UK & EU): NRV, doses, red flags