Nutrend Flexit Drink

Collagen peptides (hydrolysed collagen)· evidence: Limited

Collagen peptides are collagen from cow hide, pig skin, fish skin or chicken broken down into small pieces so they dissolve easily. The body digests them into amino acids and small peptides; it does not move the collagen straight to your skin or joints. Branded peptides (such as Verisol, Fortigel, Fortibone, Tendoforte, Naticol or Peptan) are marketed for particular uses.

For skin, many trials report small improvements in skin moisture or elasticity at 2.5–10 g a day, but a 2023 review found that the positive results came mainly from studies funded by the industry, while independent studies tended to find no effect. For joints and tendons, the evidence is smaller still: a few trials, mostly in athletes or older adults, mostly industry-linked, at 5–10 g a day.

There is no authorised health claim for collagen itself, so we make no claims about skin, joints or tendons. Any claim on a collagen product comes from added vitamins such as vitamin C. As a protein source it is incomplete, so it is not a good choice for building muscle.

Typical dose: Studies mostly used 2.5–10 g a day; many capsule products give far less

Safety: Made from animal or fish sources, so not suitable for vegetarians or vegans. Check the source if you have a fish allergy or avoid beef or pork. Generally well tolerated.

Research we looked at:
Pu SY et al. (2023). Effects of oral collagen for skin anti-aging: a systematic review and meta-analysis. Nutrients 15(9):2080.
de Miranda RB, Weimer P, Rossi RC (2021). Effects of hydrolyzed collagen supplementation on skin aging: a systematic review and meta-analysis. Int J Dermatol 60(12):1449–1461.
Khatri M et al. (2021). The effects of collagen peptide supplementation on body composition, collagen synthesis, and recovery from joint injury and exercise: a systematic review. Amino Acids 53:1493–1506.

Vitamin C· evidence: Moderate

Vitamin C (ascorbic acid, or mineral ascorbates such as sodium, calcium or magnesium ascorbate) is an essential vitamin found in fruit and vegetables. Adults need about 40 mg a day in the UK, and most people who eat fruit and vegetables get enough. The body cannot store much, and absorption falls off at higher doses, so the extra from a 1,000 mg tablet is largely passed in urine.

The best evidence on colds (a Cochrane review) found that taking vitamin C every day does not stop most people catching colds, but may shorten them slightly. People doing very heavy physical exercise are the exception, where regular vitamin C roughly halved the number of colds in trials.

A supplement makes sense if your diet is low in fruit and vegetables, if you smoke, or around periods of hard training. Most people do not need mega-doses, and fancy forms (liposomal, ester or buffered) have little evidence of meaningful benefit over plain ascorbic acid, though buffered forms can be gentler on the stomach.

Typical dose: The UK reference intake for adults is 40 mg a day (NRV on labels: 80 mg). Supplements commonly give 200 to 1,000 mg.

Safety: The FSA advises that 1,000 mg (1 g) a day or less from supplements is unlikely to cause harm. Higher doses can cause stomach pain, diarrhoea and wind. People with a history of kidney stones, haemochromatosis (iron overload) or kidney disease should speak to their GP before taking high doses. Chewable and powder forms are acidic and can affect tooth enamel.

Research we looked at:
NHS. Vitamin C. nhs.uk/conditions/vitamins-and-minerals/vitamin-c
Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev 2013;(1):CD000980.
EFSA NDA Panel. Scientific opinion on dietary reference values for vitamin C. EFSA Journal 2013;11(11):3418.
Carr AC, Vissers MCM. Synthetic or food-derived vitamin C: are they equally bioavailable? Nutrients 2013;5(11):4284-4304.

Glucosamine· evidence: Limited

Glucosamine is a building block of cartilage. In supplements it comes as glucosamine sulphate or glucosamine hydrochloride, usually made from crab and shrimp shells, or from fermented corn in vegan versions. N-acetyl glucosamine is a related form with even less research behind it.

It has been studied a lot, and the results are disappointing. Large independent trials, such as the US GAIT trial, and a big review of the research found little or no difference from a dummy pill for most people. Some earlier trials using one branded glucosamine sulphate looked better, but many of those were funded by the maker. NICE does not recommend glucosamine on the NHS, and EFSA rejected a claim that it helps keep joints healthy.

There is no authorised health claim for glucosamine, so we make no claims about what it does. If you want to try it, the dose used in studies is 1,500 mg of glucosamine sulphate a day, and it is fair to stop after about three months if you notice no difference.

Typical dose: Studies used 1,500 mg of glucosamine sulphate a day

Safety: Most glucosamine is made from shellfish: avoid unless the label says it is from a non-shellfish source if you have a shellfish allergy. Glucosamine may strengthen the effect of warfarin, so speak to your GP or pharmacist first if you take warfarin or another blood thinner. Speak to your GP first if you have diabetes, asthma or glaucoma, or are pregnant or breastfeeding. Can cause mild stomach upset.

Research we looked at:
Clegg DO et al. (2006). Glucosamine, chondroitin sulfate, and the two in combination for painful knee osteoarthritis. N Engl J Med 354:795–808.
Wandel S et al. (2010). Effects of glucosamine, chondroitin, or placebo in patients with osteoarthritis of hip or knee: network meta-analysis. BMJ 341:c4675.
NICE (2022). Osteoarthritis in over 16s: diagnosis and management. NICE guideline NG226.
EFSA NDA Panel (2009). Scientific opinion on the substantiation of health claims related to glucosamine alone or in combination with chondroitin sulphate and maintenance of joints. EFSA Journal 7(9):1264.

Vitamin B6· evidence: Limited

Vitamin B6 (pyridoxine, or the active form pyridoxal-5-phosphate, P-5-P) helps the body use protein and make red blood cells and some brain chemicals. Adults need only about 1.2 to 1.4 mg a day, and most people in the UK get this easily from meat, fish, wholegrains, potatoes, bananas and fortified cereals. True deficiency is uncommon.

For people who are not deficient, there is little good evidence that extra B6 does anything useful. It is often combined with magnesium or zinc in sports products; the B6 in these is mostly there to carry the label claims.

The bigger issue with B6 is safety. Long-term high doses can damage the nerves in the hands and feet, and this has been reported at doses sold freely in shops.

Typical dose: Adults need about 1.2 mg (women) to 1.4 mg (men) a day (NRV on labels: 1.4 mg). A supplement giving 1.4 to 10 mg is plenty.

Safety: The Food Standards Agency advises not taking more than 10 mg of vitamin B6 a day from supplements unless a doctor advises it. Taking more than this for a long time can cause loss of feeling in the arms and legs (peripheral neuropathy). Add up the B6 from all your supplements, including B complexes, magnesium/zinc products and multivitamins. Stop and see your GP if you notice tingling, numbness or burning in your hands or feet.

Research we looked at:
NHS. Vitamins and minerals: vitamin B6. nhs.uk/conditions/vitamins-and-minerals/vitamin-b
Expert Group on Vitamins and Minerals (2003). Safe Upper Levels for Vitamins and Minerals. Food Standards Agency.
EFSA NDA Panel. Scientific opinion on the tolerable upper intake level for vitamin B6. EFSA Journal 2023;21(5):8006.
Therapeutic Goods Administration (Australia) 2023. Safety review: vitamin B6 (pyridoxine) and peripheral neuropathy.

Cost per daily dose lets you compare packs of different sizes fairly.Worked out from our current prices.