Vitamin C's quiet day job in your joints

Most of us file vitamin C under winter. It is the orange juice vitamin, the one you reach for when the office starts sniffling. Fair enough, but that reputation hides its other career, the one that explains why it keeps appearing in joint formulas: vitamin C is essential to collagen, and collagen holds you together.

Collagen is the most abundant protein in the human body. It is the scaffolding fibre in cartilage, tendons, ligaments, skin and bone, arranged in ropes and lattices that give those tissues their strength. And your body cannot build it properly without vitamin C. The enzymes that lock collagen fibres into their strong, cross-linked form need vitamin C on hand to do the job. This is not a fringe theory. It is one of the best-established relationships in nutrition science: vitamin C contributes to normal collagen formation, for the normal function of cartilage and bone.

History learned this the hard way. Fresh oranges and lemons became precious cargo on long sea voyages because sailors deprived of vitamin C for months found their connective tissue could no longer maintain itself. The answer, when it came, was citrus in the hold. It remains one of the clearest demonstrations in all of nutrition that a single nutrient can carry structural responsibility.

There is a quirk that makes the story stranger: most animals manufacture their own vitamin C and never give it a thought. Humans, along with guinea pigs and a handful of others, lost that ability somewhere in our evolutionary past. We are one of the few creatures that must eat it, every day, or run short.

Which brings us back to joints. Cartilage is largely collagen by dry weight, and tendons and ligaments more so. A joint formula that supplies glucosamine and chondroitin but ignores collagen's needs is delivering bricks without mortar. That is why Koru Joint, made by Koru Nutrition in Christchurch, includes vitamin C in the nourishing phase of its formula, sitting alongside glucosamine precisely for this collagen connection.

Food should still come first, and New Zealanders hold a good hand. A single kiwifruit delivers roughly the daily requirement on its own, outscoring an orange comfortably. Capsicum, broccoli and berries all contribute.

So keep the winter habit if you like. Just know that vitamin C's day job runs all year, in every tendon and every joint, quietly helping to build the protein that keeps the whole structure standing.