Collagen supplements might make your skin more elastic – but the evidence is weak.

Collagen is hugely hyped. This protein, which is important to the structure of skin and joints, has been presented as a miracle cure for everything from wrinkles to poor sleep.

Production of collagen, the most abundant protein in the body, naturally slows with age – whether you protect your skin from the Sun or not. To compensate, collagen supplementation has become a booming business. One aficionado is Bryan Johnson, the tech entrepreneur who has become a one-man experiment for how to prolong your life, who says he takes 25g (0.9 ounces) of collagen peptides every day.

But collagen is not always well understood. While there is some evidence that supplementing with this molecule has health benefits, research is limited. The main risk of taking it as a supplement may be of wasting money – there are few known side effects – but is the scientific evidence keeping pace with the marketing claims?

To start with the basics, "collagen is only found in animal connective tissue", notes Andrea Soares, a registered dietitian in Georgia, US, who is part of the Top Nutrition Coaching network, a company which helps to connect people with dietitians in their area.

Collagen products come from a variety of animals: cows, pigs, chickens and fish. Gelatine, which is used to make sweets, jelly and the capsules for pharmaceuticals, is a form of collagen. "Some plant-based supplements claim to be 'vegan collagen', but what they actually contain are collagen-boosting ingredients like vitamin C, amino acids and minerals that help your body make its own collagen," says Soares. "If you're vegan, you might want to spend your money on a well-rounded diet instead of plant-based 'collagen' supplements that don't actually contain collagen."

Different types of collagen appear to work differently. Hydrolysed collagen (collagen hydrolysate) is collagen which has been broken down into short chains of amino acids known as peptides. These get broken down further as they move through the digestive system. On the other hand, undenatured (raw) type II collagen is a component of cartilage surrounding joints. In theory it can help replenish collagen around the joints, says David Hunter, a rheumatology clinician researcher at the University of Sydney, focusing on osteoarthritis. Type II collagen is also broken down into amino acids in the stomach, though hydrolysed collagen tends to be better absorbed by the body.

In addition to the wide variety of sources and types of collagen, the substance is packaged into many different forms, from bars to drinks. Compared to powders and liquids, "tablets and gummies often have less collagen per serving and may contain added sugars or fillers," Soares says. And while consuming food rich in protein and vitamin C generally helps our bodies to make collagen, the amount of collagen present in food like bone broth varies. She advises those taking collagen as a supplement to opt for a powder or liquid, with at least 5-10g (0.2-0.4 ounces) of collagen per dose.

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........

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