Low vitamin C tends to show on you: bruising easily, wounds healing slowly, and rough or dry skin, alongside general tiredness. Your body uses it to build collagen, protect cells, and absorb iron from plant foods, so a shortfall over time is associated with all of those.
Unlike the fat-soluble vitamins, vitamin C isn't stored, so you need a steady supply rather than being able to bank it. A few thin days aren't a problem; a consistently low intake over weeks is where the shortfall builds.
It's one of the easier gaps to close through food. Citrus fruits, strawberries, kiwi, bell peppers, and tomatoes are all rich in it, and because it's spread across so many everyday fruits and vegetables, most varied diets cover it.
Adults need around 85 mg a day. There's a firm ceiling too: it's best not to exceed 2,000 mg daily, since very high doses can upset your stomach and cause other problems.