Collagen harms

Short answer

No serious side effects were reported in the studies reviewed; however, these studies are small and short, and safety is mostly not the primary outcome. ^[4] Three topics need to be addressed separately: allergy to fish-derived collagen, variable metal levels in marine-sourced products, and protein load in chronic kidney disease. ^{[1] [2] [3]}

What are the side effects of collagen supplementation?

Side effect data come from the safety sections of collagen studies. They consist of three different examples, and all have limits.

• Sarcopenic men, 12 weeks, 15 g per day of collagen peptide (53 participants): None of the dropouts was due to a side effect; no serious adverse events were seen, and no pathological finding was detected in routine blood tests. Part of the study’s costs was covered by the manufacturer. ^[4]
• Healthy volunteers, single dose, hydrolysates from different sources (pilot, 6 people): All products were well tolerated, and no adverse events were reported on the study days. The study was funded by a collagen manufacturer, and some of the authors are employees of this manufacturer. ^[5]
• Knee osteoarthritis, 40 mg per day of undenatured type II collagen, 180 days (191 participants): The authors reported that safety results did not differ between groups (placebo, glucosamine-chondroitin, undenatured type II collagen); mild digestive events such as heartburn were listed in similar numbers in the three groups (2, 3 and 2 events). The study was sponsored by a supplement company; two authors are employees of that company. ^[6]

Because the frequency of digestive complaints was not a primary outcome in these studies, no firm rate can be given. In addition, EFSA has explicitly stated that its assessment of collagen claims is not an assessment of the product’s safety. ^[7]

The participants in the studies cited on this page are older men, postmenopausal and older women, athletes and healthy young volunteers; safety in pregnancy, breastfeeding and children has not been tested by these studies.

Does fish collagen cause allergic reactions?

The best-known allergen in fish allergy is parvalbumin. The study by Kobayashi and colleagues, stating that collagen has been described as a second fish allergen but its properties are not sufficiently known, examined extracts prepared from the heated flesh of 7 bony and 4 cartilaginous fish species. Although collagen was broken down by high-temperature treatment (10 minutes at 140 °C or 320 minutes at 100 °C), the IgE reactivity of patients’ sera did not change after heating; reactivity to extracts of cartilaginous fish was lower than to those of bony fish. In one patient who underwent a skin prick test, all extracts produced an allergic reaction. ^[1]

This study was done with fish flesh extracts; it did not test collagen supplements. That is, the conclusion “fish collagen supplements cause reactions in people with fish allergy” does not follow directly from it; it was only shown that fish collagen can be allergenic and that this property is not easily removed by heat.

Is there heavy metal in marine collagen?

A study in Italy measured fish- and jellyfish-derived collagen supplements for lead, cadmium, chromium, arsenic and mercury. For four commercial brands (Atlantic cod, pangasius, jellyfish and tilapia-derived), a total of 120 samples were examined, 6 samples from each of 5 production batches per brand; in addition, the authors prepared an extract from mackerel skin. ^[2]

Results:

• Arsenic was the most abundant element (mean 0.59 ± 0.28 mg/kg); the lead mean was 0.13 ± 0.02 mg/kg.
• There was a marked difference between brands; mercury could be detected in only 12% of samples.
• There were no measurable toxic metals in the jellyfish and mackerel skin extract samples.
• No sample exceeded EU legal limits, and the calculated daily intakes remained below tolerable daily intakes; the authors recommended that food safety regulations be updated to take into account the cumulative risk of using more than one contaminated supplement at the same time. ^[2]

The study was funded by the Italian Ministry of Health; four brands and a limited number of samples do not represent all products sold in Türkiye. Because the results show variability between brands, they cannot be generalized as “marine collagen always contains metals” or “never contains any.” ^[2]

Is using collagen powder a problem in kidney disease?

Collagen peptide is a protein supplement: in the study in sarcopenic men, 15 g per day of collagen peptide was given as a “protein supplement.” ^[4] In chronic kidney disease (CKD), total protein intake is regulated by guidelines. According to the executive summary of the KDIGO 2024 guideline, maintaining a protein intake of 0.8 g/kg body weight per day is recommended in adults at stages G3–G5 (recommendation grade 2C: weak, that is, a conditional recommendation; low certainty of evidence); avoiding high protein intake above 1.3 g/kg/day in adults at risk of progression is a practice point. The same guideline also states that higher protein and calorie targets may be considered in older adults in conditions such as frailty and sarcopenia, and asks that the protein target be determined according to the person and stage with a renal dietitian or a trained nutrition professional. ^[3]

KDIGO does not address collagen specifically; the limits reported are for total dietary protein. The difference in amount also matters: the 15 g used in hydrolyzed peptide studies is 375 times the 40 mg per day in the undenatured type II collagen study; protein load is a question only for peptide products at the gram level. As an arithmetic example, for a person of 70 kg the 0.8 g/kg value is 56 g of protein per day; an amount of 15 g of collagen peptide corresponds to about 27% of this. This is not a dose recommendation; it is a calculation given to show that collagen powder is added to total protein.

Why is this safety data limited?

The size and duration of the three studies are very different: 53 people and 12 weeks, 6 people and a single dose, 191 people and 180 days. ^{[4] [5] [6]} Each was done with a specific product, in a specific group of participants (for example older men or patients with osteoarthritis), and mostly with the support of the product’s owner or manufacturer. The single-dose study describes itself as a pilot study of 6 people; the participants are healthy, nonsmoking people aged 19–50. ^[5] The knee osteoarthritis study enrolled people aged 40–75 with moderate-to-severe knee osteoarthritis and a body mass index of 18–30. ^[6] Side effects are not the primary outcome of these studies; studies of this size are not expected to capture rare or delayed events. The statement “no side effects were reported” is therefore not equivalent to “it is harmless”; it only says that no marked problem was seen under the conditions examined.

Who should be extra careful with collagen supplements?

• People with fish allergy: In marine-sourced products, the type of raw material matters (above). ^[1]
• People with chronic kidney disease: The total protein target is determined with the physician and dietitian. ^[3]
• Pregnant and breastfeeding women and children: There are no safety data in these groups in the studies reported.
• People on regular medication: No drug interaction data for collagen are included in the evidence reviewed; for people on medication, assessment by a physician or pharmacist takes priority.
• People who avoid certain animal sources for religious or dietary reasons: Different sources such as bovine, porcine, fish and chicken are used in studies and products; label information may not be equally detailed for every product.

This guide does not recommend a personal dose or product.

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