Taking a collagen supplement does not mean that collagen goes straight to your bones, joints, tendons, or skin. Before your body can use it, it must go through a far more complex process: digestion, absorption, and distribution of its components.
In recent years, collagen has become one of the standout supplements. It is touted as a help for caring for joints, maintaining skin, strengthening bones, or promoting the health of tendons and ligaments. But there is a fairly widespread idea that needs clarification: when we take collagen, our body does not receive “ready-to-use collagen” that automatically targets a joint or tendon. What we actually introduce are collagen proteins or collagen peptides that our digestive system processes.
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What happens when you take collagen?
The collagen found in supplements usually comes from animal tissues and is commonly presented as hydrolyzed collagen or collagen peptides. When ingested, the digestive process begins. In the stomach and, subsequently, in the small intestine, the proteins break down into smaller fragments. A portion ends up converted into free amino acids, while another portion may pass through the intestine as small peptides.
These components enter the bloodstream and become available for the body to use. And here is the key: the body does not carry a label that says “these amino acids are for the knee” or “these are for the skin.” Once absorbed, the amino acids become part of the pool of nutrients available to the organism. The body will use them wherever needed and according to its metabolic priorities.
So, does the collagen I take end up turning into collagen?
It can contribute to that, but not automatically. The body continually manufactures its own proteins. To produce collagen it needs amino acids, energy, vitamin C, and other micronutrients and cofactors that participate in the process. Therefore, the amino acids from a collagen supplement can be used as raw material to synthesize new proteins, including collagen. But those amino acids do not have a predetermined destination.
Imagine we take 10 grams of collagen peptides. After digestion and absorption, their components join the body’s amino acid pool. Some of it may be used to synthesize collagen; some may be employed to build other proteins; and, depending on energy needs and metabolic demands, some amino acids may also end up used as an energy source.
We cannot claim that a specific amount of the supplement ends up directly in bones, tendons, or joints. That is why the idea that “I take collagen and that collagen goes to my knee” is an oversimplification.
Where does the idea of 10% come from then?
The assertion that only around the 10% of ingested collagen ends up targeting bones, joints, or tendons has gained popularity. However, it is prudent to be cautious with this figure. There is no universal rule that exactly 10% of each collagen dose will improve those tissues. The fate of amino acids depends on many factors, such as nutritional status, the body’s needs, protein synthesis and breakdown, and the total amount of proteins and nutrients available.
Therefore, it is more accurate to say that only a fraction of the components we ingest will end up participating in the synthesis of collagen for certain tissues, and that we cannot assign a fixed percentage to bones, tendons, or joints. Moreover, that an amino acid is used to make collagen does not automatically mean that this process will produce a clinically noticeable improvement.
The collagen does not act as a “filler” for joints
This distinction is especially important when we talk about supplements aimed at athletes. A tendon, a ligament, cartilage, or bone are living tissues that are continually undergoing formation, repair, and degradation. The body adapts its metabolism to stimuli such as exercise, mechanical load, rest, and nutrient availability.
Therefore, if we aim to care for our joints or tendons, it does not make much sense to think solely in terms of “providing collagen.” The stimulus the tissue receives also matters.
Strength training, for example, provides a fundamental mechanical cue to maintain and adapt different structures of the locomotor system. Adequate energy and protein intake, along with proper micronutrients, also forms part of the context. The supplement, in any case, is just one piece of the puzzle.
That collagen doesn’t reach the joint directly doesn’t mean it’s useless.
Does this mean taking collagen is completely useless?
No. Here it is important not to go to the opposite extreme. The fact that collagen doesn’t arrive directly at the joint does not mean it is useless. Some studies have observed that certain collagen peptides, consumed in specific amounts and over prolonged periods, can produce modest improvements in some markers or symptoms related to joint health. Its possible usefulness in other tissues and situations has also been explored. But these results should not be interpreted as: “I take collagen and my body automatically makes more collagen.” The reality is more nuanced and interesting.
The collagen peptides provide amino acids —with a high presence of glycine, proline, and hydroxyproline— and certain peptides can also act as metabolic signals. The body may respond to these nutrients and signals by modifying certain processes related to the extracellular matrix and connective tissue metabolism.
But the effect depends on the dose, the type of product, the tissue, the person’s state, and the overall context of diet and training.
The protein doesn’t know the name of your injury
A helpful way to understand this is to think of amino acids as building blocks. When you eat collagen, you are not delivering a finished piece of a joint to the body. You are supplying raw material and certain peptides that enter a much larger system. The body decides what to do with them.
If it needs to manufacture collagen to renew tissues, it may use those amino acids. If it needs to synthesize other proteins, it will use them for that. And if there is an excess of certain nutrients relative to the moment’s needs, your metabolism will follow other routes.
That is why taking more collagen does not automatically mean you will produce more collagen. The body does not operate as a factory where increasing raw material quantity automatically guarantees an increase in final output.
So what should we expect from a supplement then?
A reasonable expectation would be to view collagen as a potential complementary tool, not a miracle cure or a substitute for proper nutrition. If a person has a diet sufficient in protein, consumes fruits and vegetables, maintains an adequate intake of vitamin C and other micronutrients, trains progressively, and rests adequately, the supplement may make sense in certain circumstances.
But no supplement alone can compensate for a poor diet, a prolonged energy deficit, a lack of training, or insufficient recovery.
And we must not forget something fundamental: the body already manufactures collagen continually. We do not need to ingest collagen for that process to exist. What supplementation provides is an additional source of certain amino acids and peptides that the body can use.
The takeaway: less magic and more physiology
The next time you see a collagen supplement promising to “reach your joints,” it’s worth remembering what actually happens.
You take the supplement. You digest it. Its proteins fragment. The amino acids and small peptides are absorbed and enter the circulation. From there, the body incorporates them into its metabolism and decides how to use them.
Some of it may contribute to the synthesis of new proteins, including collagen in different tissues. Some of it will have other metabolic destinations.
Therefore, it isn’t correct to think that the ingested collagen directly turns into collagen in our tendons, bones, or joints, nor that there exists a fixed percentage —like the famous 10%— that inevitably ends up there.
Collagen can be useful, but not because the supplement travels directly to where we need it. It is the body, with its complex mechanisms of digestion, absorption, distribution, and protein synthesis, that determines what happens to what we have ingested.
And perhaps that is the best way to understand supplements: they are not bricks we place directly into a tissue; they are nutrients that the body incorporates into a much more sophisticated biological machinery.