Our Connective Tissue

Your connective tissue is the structural framework that holds your body together. Skin, bone, cartilage, tendons, ligaments, fascia, blood vessel walls, the gut lining, and the cornea of your eye are all connective tissue. So is the matrix that sits between every cell in every organ. If you stripped away all the muscle, nerves, and organs and left only the connective tissue, you would still see a recognisable outline of a human being.

Connective tissue does more than hold you together. It transmits force (tendons), absorbs shock (cartilage), provides structural integrity under pressure (blood vessels), creates barriers (skin, gut lining), and serves as the scaffold that other tissues are built on (bone). Its quality determines how your body moves, ages, heals, and resists damage. Most of what people describe as "aging," wrinkles, joint stiffness, slower healing, weaker bones, thinning skin, is fundamentally connective tissue decline.

What connective tissue is

Connective tissue is built and maintained primarily by fibroblasts, the workhorse cells that produce and organise the structural materials that everything else sits in. Specialised variants exist in different tissues: chondrocytes in cartilage, osteoblasts in bone, but fibroblasts are the general-purpose builders throughout the body.

What fibroblasts actually build is called the extracellular matrix (ECM), the framework that exists outside cells and gives tissue its shape, strength, and resilience. The ECM is made up of three main components:

Collagen is the main structural protein, providing tensile strength.

Elastin is collagen's partner. Where collagen is rigid, elastin is stretchy. It's what allows skin to snap back when pinched, blood vessels to expand and contract with each heartbeat, and lungs to inflate and recoil.

Ground substance is the hydrated gel that fills the space between collagen and elastin fibres. It's made of hyaluronic acid, proteoglycans, and glycosaminoglycans (GAGs). This gel holds water, lubricates joints, and gives tissue its plumpness.

All three components work together. Collagen provides the framework, elastin provides flexibility, and the ground substance fills the gaps and hydrates everything.

Collagen

Collagen is the single most abundant protein in the human body, making up roughly 30% of all protein in you. It's the primary structural material in skin, bone, tendons, ligaments, cartilage, blood vessel walls, the gut lining, teeth, the cornea, and the fascia wrapping every muscle in your body.

Collagen isn't one protein. There are at least 28 identified types, but a handful do the vast majority of the work:

Type I is the dominant collagen in the body, roughly 90% of total collagen. It's the primary structural protein in skin, bone, tendons, ligaments, teeth, and the walls of organs. When people talk about "collagen" without specifying a type, they almost always mean type I

Type II is the main collagen in cartilage. It forms a flexible mesh that gives cartilage its shock-absorbing properties. When cartilage degrades in osteoarthritis, type II collagen is being lost

Type III is found alongside type I in skin, blood vessels, and internal organs. It's the first collagen produced during wound healing, forming a rapid provisional scaffold that type I later replaces with stronger, more organised fibres. Younger skin has a higher ratio of type III to type I, which is partly why it feels softer

Type IV forms thin sheet-like structures called basement membranes, the layers that underlie skin, line blood vessels, and separate tissues from each other.

Type V is found on cell surfaces, in hair, and in the placenta. It helps regulate the diameter of type I fibres during assembly

The triple helix structure

What makes collagen structurally unique is its shape. Three polypeptide chains (called alpha chains) wind around each other to form a rigid triple helix, like three ropes braided together. This triple helix is what gives collagen its extraordinary tensile strength, gram for gram, type I collagen fibres are stronger than steel.

Roughly one third of all amino acids in collagen are glycine, the smallest amino acid, which fits into the tight interior of the helix where no larger amino acid could. The repeating pattern is glycine-X-Y, where X is usually proline and Y is usually hydroxyproline. This glycine-proline-hydroxyproline repeat is the signature sequence of collagen and the reason collagen supplements are so rich in these three amino acids.

Hydroxyproline is particularly important because it's what locks the triple helix into its stable shape. It's created by an enzyme called prolyl hydroxylase, which modifies proline after the chain is built but before the helix forms. This enzyme requires vitamin C as a cofactor, which is why vitamin C deficiency (scurvy) causes collagen to fall apart. Without hydroxylation, the triple helix can't hold together, and without a stable helix, connective tissue throughout the body degrades.

Sailors historically lost teeth, had bleeding gums, and had old wounds reopen because the collagen holding everything together was unravelling.

How collagen is built

Collagen synthesis is a multi-step process that starts inside the cell and finishes outside it:

Inside the cell (fibroblast):

The cell reads the collagen recipe from its DNA and uses it to build long protein chains, the raw material for collagen

Enzymes modify those chains by adding hydroxyl groups to specific spots. This step is what allows the chains to lock into the triple helix shape later (requiring both vitamin C and iron)

Three modified chains wind around each other to form the triple helix, the basic collagen unit

The cell packages the new collagen unit and ships it out into the surrounding tissue

Outside the cell:

The new collagen unit gets trimmed into its functional form, ready to assemble into a fibre

The trimmed units line up alongside each other, building into longer fibres

An enzyme called lysyl oxidase locks neighbouring fibres together with chemical cross-links, the bonds that give collagen its real mechanical strength. This enzyme requires copper to function, which is why copper deficiency weakens connective tissue.

The cross-linking step is critical. Without it, you have individual collagen molecules floating around with no structural integrity. With it, you have fibres that can resist enormous tensile forces. Cross-linking also gets mentioned often in the context of aging because the type of cross-links changes over time.

Collagen lifecycle

The body continuously breaks down old collagen and replaces it with new, a process called remodelling. This happens through two opposing groups of enzymes:

MMPs (matrix metalloproteinases) are the demolition crew. They cut up old, damaged, or disorganised collagen so it can be cleared and replaced

TIMPs (tissue inhibitors of metalloproteinases) put the brakes on MMPs to prevent excessive breakdown

Fibroblasts lay down new collagen to replace what was cleared

The balance between these three determines whether your collagen network is being maintained, lost, or rebuilt. Too much MMP activity (which happens in chronic inflammation and UV exposure) tips the scale toward breakdown. Too little fibroblast activity (which happens with aging, cortisol, and oestrogen decline) tips it toward depletion.

The rate of turnover varies enormously by tissue. The gut lining turns over every 3-5 days, so collagen there is replaced rapidly. Skin dermal collagen turns over much more slowly, on the order of months to years. Tendon collagen is among the slowest, with a half-life measured in years to decades, which is why tendon injuries take so long to heal and why tendons are particularly vulnerable to accumulated damage.

This variable turnover rate is also explains why different tissues respond to collagen supplementation on different timescales.

Age-related decline

Starting in the mid-twenties, collagen production declines by roughly 1-1.5% per year. By age 40, a significant portion of the total collagen in the body has been lost, and by 60 the decline is steep. This single fact underlies a remarkable number of aging symptoms: thinner skin, wrinkles, joint stiffness, slower wound healing, weaker bones, reduced tendon resilience, and gut barrier deterioration.

Glycation. Glucose in the blood reacts with collagen fibres and forms permanent abnormal bonds called AGEs (advanced glycation end-products). These bonds stiffen the collagen matrix, making it rigid and brittle instead of flexible and resilient. The body can't undo them, it can only break down the glycated collagen and replace it, and these stiffened fibres are harder for the normal cleanup enzymes (MMPs) to break down in the first place. So they accumulate. Higher blood sugar means more glycation, faster accumulation, and faster connective tissue aging. This is why diabetics age faster in virtually every connective tissue and why low blood sugar control is an anti-aging strategy. The same process stiffens collagen in skin (wrinkles), blood vessels (arterial stiffness and hypertension), kidneys, and the lens of the eye (cataracts).

The combination of reduced production, accumulated glycation, and pathological cross-linking is why aging connective tissue behaves so differently from young connective tissue.

What accelerates collagen loss:

UV radiation is the single biggest external destroyer of collagen in skin. It directly fragments collagen fibres and upregulates MMPs.

Chronic inflammation suppresses fibroblast activity and upregulates MMPs.

Smoking introduces free radicals that attack collagen directly and reduces blood flow to the skin, starving fibroblasts of oxygen and nutrients

High sugar intake accelerates glycation

Cortisol from chronic stress directly inhibits collagen synthesis and thins the skin

Oestrogen decline in women accelerates collagen loss significantly post-menopause. Oestrogen is a direct stimulator of fibroblast activity and collagen production.

Collagen across the body

Collagen sits in nearly every tissue, which is why so many different conditions and interventions on this site come back to it.

Bone is roughly 35% collagen by weight, the flexible scaffold that calcium and phosphate minerals deposit onto. Without the collagen, bone would be brittle like chalk. Without the minerals, it would bend like rubber. Osteoporosis involves loss of both.

Tendons and ligaments are almost pure type I collagen, arranged in parallel bundles to transmit force in one direction. This is why tendons handle huge loads along their length but tear under shearing or twisting forces.

Cartilage is mostly type II collagen in a hydrated matrix of proteoglycans. The collagen provides structure, the proteoglycans hold water, and the combination is what absorbs shock in joints. When type II collagen degrades, cartilage loses its framework. This is osteoarthritis.

Gut lining uses type I and III collagen as the structural layer underneath the intestinal cells. If this layer weakens, the gut barrier weakens.

Blood vessels use type I and III collagen for structural support in their walls. Stiffening of this collagen with age contributes to arterial stiffness and hypertension.

Skin. The dermis is primarily type I and III collagen, with elastin providing recoil and hyaluronic acid providing hydration. Every visible sign of skin aging traces back to changes in this collagen network.

Collagen is the structural foundation of nearly every tissue in the body, and its decline is a root cause of problems across multiple systems simultaneously. This is why compounds that stimulate collagen synthesis

GHK-Cu ,

Vitamin C ,

Topical Retinoids) or provide building blocks

Hydrolyzed Collagen have such broad-ranging effects.