Collagen bioavailability and daltons: molecular weight made simple

Short answer: bioavailability tells you what share of the collagen you swallow reaches the blood, and molecular weight in daltons (Da) tells you how large its peptides are. Collagen that had undergone further enzymatic splitting was absorbed faster and in greater amounts in a Danish study with 10 men (Skov et al., 2019). But the differences need not be large: in a study that compared fish, pork and bovine hydrolysates, the bovine ones at both 2,000 and 5,000 Da, the uptake of free hydroxyproline was comparable (Virgilio et al., 2024). The well-known 500 Da threshold comes from research on the skin, not the intestine (Bos and Meinardi, 2000). So take the number on the pack as information about the raw material, not as a promise of an effect.

Bioavailability, also called biological availability, is the share of a substance from a swallowed dose that reaches the bloodstream. For medicines it is measured fairly directly. For collagen it is more complicated: it is a protein, the body breaks it down into amino acids and short peptides, and these mix with amino acids from other food.

Researchers therefore rely on the amino acid hydroxyproline. Collagen is rich in it, just as it is in glycine and proline (Skov et al., 2019), so when hydroxyproline in the blood rises after drinking collagen, it is a trace of the collagen that was drunk. Both free hydroxyproline and hydroxyproline bound in peptides are measured. In a study with five men, peptides made up about 30% of all hydroxyproline in the blood (Ohara et al., 2007).

The dalton (Da) is a unit of molecular mass. One dalton is roughly the mass of a hydrogen atom, a water molecule has 18 Da and glucose 180 Da. A collagen hydrolysate is a mixture of peptides of different lengths, so the figure in daltons on the pack describes the typical size of the peptides in the raw material.

Pro-Hyp is the main collagen peptide found in the blood after drinking collagen (Iwai et al., 2005). The range of 3,000 to 6,000 Da for typical hydrolysed collagen is given in the review by León-López et al. (2019).

In the intestine, collagen peptides are split further. Free amino acids then enter the cells of the intestinal lining, along with dipeptides and tripeptides carried by the transporter PEPT1. It can handle practically any dipeptide and tripeptide, but it does not take up peptides of four or more amino acids (Daniel, 2004). That is why, after drinking collagen, mainly short peptides are found in the blood, most of all the dipeptide Pro-Hyp, peaking after 1 to 2 hours (Iwai et al., 2005).

However, longer peptides can also pass through the intestinal wall. In experiments in mice, peptides of 2,500 to 15,000 Da were also found after passage through the intestine (Oesser et al., 1999). The idea that collagen above a certain dalton threshold “does not get through at all” therefore does not match what the studies saw. We describe it step by step in the article Collagen absorption.

More extensively split collagen was absorbed faster, but the differences are not as big as adverts suggest. Two studies in humans:

• A Danish study with 10 men compared 35 g of collagen that had undergone further enzymatic splitting with the same dose without this splitting and with a placebo. After the split collagen, glycine, proline and hydroxyproline in the blood rose faster and more overall (Skov et al., 2019).
• A randomised double-blind study compared hydrolysates from fish, pigs and cattle, the bovine one in two sizes, 2,000 and 5,000 Da. The uptake of free hydroxyproline was comparable for all of them, and all led to substantial levels of the measured substances in the blood. Most of the authors work for a collagen manufacturer. The authors themselves write that larger studies are needed (Virgilio et al., 2024).

So the results are mixed: further splitting sped up absorption, but no big difference was seen between 2,000 and 5,000 Da. The dose also plays a role: in four volunteers, the level of peptides in the blood rose with the amount of collagen drunk (Shigemura et al., 2014).

You know the 500 Da threshold from collagen adverts, but it originally belongs to the skin. The 500 dalton rule says that only substances up to about 500 Da pass through intact skin, and larger molecules do not penetrate the horny layer (Bos and Meinardi, 2000). For collagen in a cream this holds: the whole collagen molecule is many times larger and therefore stays on the surface of the skin. For collagen you drink, what matters most is digestion into short peptides in the intestine. We describe the difference in the article Collagen vs. collagen cream.

The human studies we went through for this article do not give collagen bioavailability as a single percentage. They track how fast and how high hydroxyproline and collagen peptides rise in the blood (Shigemura et al., 2014; Virgilio et al., 2024). When you see a percentage on a pack, ask which study it comes from, how many people it was measured in and at what dose.

The marine collagen from collalloc has a molecular weight of around 500 Da and an absorbability of 95%.

1. How many daltons? Look for a specific number, not just “low molecular weight” or “small molecule”.
2. From what raw material? Fish, cattle or pigs. The composition of peptides in the blood depends on the raw material (Ohara et al., 2007), and so does who must not take the collagen because of an allergy, more in the article Marine or bovine collagen?
3. Where does the absorbability figure come from? A study with a stated dose and number of people carries more weight than a percentage without a source.

collalloc kolagen is marine collagen from North Sea fish, and the raw material is hydrolysed in Switzerland to a molecular weight of around 500 Da. A sachet contains 3,300 mg of type I, II and III collagen without fillers, colourings or sweeteners and is stirred into a cold or lukewarm drink up to 60 °C. The liquid collalloc NANO 2.0 contains 700 mg of marine collagen and 80 mg of vitamin C in 1 ml. Vitamin C contributes to normal collagen formation for the normal function of skin. We test microbiology in every batch and heavy metals every month.