Can the building blocks of connective tissue support skin, joints and muscle as we age?
TL;DR: Collagen peptides have the strongest human evidence, with randomised trials showing modest improvements in skin hydration, elasticity and wrinkles, plus some joint-comfort benefits. Glycine is a key collagen amino acid with emerging mechanistic interest, but human longevity data are sparse. Neither has been proven to extend lifespan.
Collagen is the main structural protein in skin, tendons, cartilage, bones and blood vessels. After the age of 25–30, the body produces roughly 1% less collagen per year. This contributes to wrinkles, sagging skin, joint stiffness, reduced bone density and slower wound healing.
Collagen supplements are usually hydrolysed (broken into short peptides) to improve absorption. Types I and III dominate skin and vascular collagen; type II is the main form in cartilage.
Several randomised controlled trials in women aged 35–65 have found that daily hydrolysed collagen peptides:
Effects usually appear after 8–12 weeks of consistent supplementation at 5–10 g/day. For joints, collagen peptides and undenatured type II collagen have shown modest reductions in activity-related knee discomfort in athletes and older adults (Clark et al., 2008).
Important caveats:
Glycine makes up about one-third of collagen's amino acid sequence. Beyond structure, glycine is needed for:
Some researchers argue that modern muscle-heavy diets are low in glycine relative to methionine, and that "glycine restriction" may contribute to accelerated ageing in animal models. However, human intervention trials testing glycine alone for longevity are limited. A 2018 mouse study by Brull et al. suggested glycine supplementation improved mitochondrial function and lifespan in aged mice.
Methionine is an essential amino acid found in high amounts in meat, eggs and dairy. Glycine is thought to buffer some of the metabolic effects of high methionine intake by supporting methylation reactions and reducing homocysteine. The practical implication is that collagen or glycine supplementation may be more useful for people on high-protein, low-connective-tissue diets than for those already eating a lot of bone broth, skin or gelatin.
| Goal | Form | Typical dose | Notes |
|---|---|---|---|
| Skin ageing | Hydrolysed collagen peptides | 5–10 g/day | Look for type I/III; 8–12 weeks for visible effects |
| Joint comfort | Hydrolysed collagen or undenatured type II | 10 g/day (collagen) or 40 mg/day (UC-II) | UC-II has smaller evidence base but some positive trials |
| General glycine supplementation | Glycine powder | 3–5 g/day, often before bed | Cheap and well tolerated; can be mixed into drinks |
| Sleep support | Glycine powder | 3 g before bed | Small Japanese trials suggest improved sleep quality |
Collagen and glycine are generally well tolerated. Collagen is not suitable for vegetarians or vegans (it is derived from animal connective tissue). Glycine may interact with clozapine and some kidney medications; people with kidney disease should consult a clinician before taking high-dose amino acids.
Collagen is not a complete protein, so it should not replace dietary protein from varied sources. It should also not be relied upon as a treatment for osteoporosis, arthritis or skin disease without medical advice.
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These sources are referenced inline throughout the article and listed below for full transparency.
"Oral supplementation of specific collagen peptides has beneficial effects on human skin physiology." Randomised trial showing improved skin elasticity.
View DOI"Daily consumption of the collagen supplement Pure Gold Collagen reduced visible signs of ageing." Open-label trial in UK/European women.
View DOI"24-Week study on the use of collagen hydrolysate as a dietary supplement in athletes with activity-related joint pain." Modest joint-comfort benefits.
View DOI"Glycine ingestion improves subjective sleep quality in human volunteers." Early human sleep trial using 3 g glycine before bed.
View DOI"Glycine supplementation extends lifespan in mice and improves mitochondrial function." Preclinical evidence for glycine's role in ageing.
View DOICollagen peptides do not reverse ageing, but several randomised trials show improvements in skin elasticity, hydration and wrinkle depth, plus modest benefits for joint comfort. Effects on lifespan have not been studied in humans.
Glycine is the simplest amino acid and makes up about one-third of collagen. It is also used in glutathione synthesis, DNA methylation and detoxification pathways. Some researchers argue that modern diets are relatively deficient in glycine compared with methionine.
Most skin and joint trials use 5–10 g/day of hydrolysed collagen peptides. Higher doses up to 15 g/day have been studied for athletes and older adults. Benefits are usually seen after 8–12 weeks.
Marine collagen is often marketed as more bioavailable because it has smaller peptides and is mostly type I. Bovine and porcine collagens provide both type I and type II. The evidence base is larger for bovine/porcine collagen, but marine collagen also shows benefits in trials.
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