Here you go:
Overall, many marketing claims made about oral collagen products don't stand up to scrutiny. In the European Union, "no health claims for collagen supplements have got the green light," explains Leng Heng, a senior scientific officer for human nutrition at the European Food Safety Authority (EFSA).
EFSA is the EU agency that assesses risks related to novel foods. When they took a look at collagen, they concluded that the health claims submitted about it so far were not supported by enough high-quality evidence. They were "not sufficiently defined, lacked supporting human studies, or relied on evidence from animal and laboratory research, which cannot predict effects in humans," says Heng. She points out that claims such as the idea that collagen helps to maintain skin elasticity, or that it improves joint functioning, have not yet been demonstrated sufficiently by scientific research.
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Potential industry bias is a key concern for determining rigour, Hunter says. Many collagen studies are funded by supplement companies or authored by employees of these companies. Conflicts of interest are supposed to be declared in academic papers, but this does not always happen. For example, one published paper includes five of seven authors who stated an affiliation to supplement companies, though no further information was given in the conflicts of interest section. (In response to a BBC query, the publisher of this paper, Elsevier, stated that the paper is now under investigation.)
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"The reality for many of these studies is that it's hard to find any that are completely independent of industry," Hunter says. Influencers sometimes tout poor-quality research and may promote higher dosages of supplements than is recommended by health authorities. Even systematic reviews and meta-analyses – large-scale reviews of the evidence, which pull together the results of multiple studies – can be compromised by the quality of the underlying studies. Hunter and his coauthors assess the risk of bias from such studies, including industry involvement.