Oct 9, 20264 min read

What Exactly Does Vitamin C do?

Vitamin C might be the most-taken supplement there is. It’s in your orange juice, your multivitamin, the fizzy tablets you reach for the moment your throat feels scratchy. Most people treat it as the thing you take to fight off a cold.

But the cold connection is the weakest part of the story. Vitamin C does its most important work somewhere people rarely look: it’s what your body uses to build collagen, the protein that holds your skin, and a lot else, together. This is a quick tour of what it does, what it doesn’t, and how much you need.

What It Does

Collagen is where vitamin C earns its place. Collagen is the scaffolding of your skin, the protein that keeps it firm. Your body builds it constantly, but the fresh fibers don’t hold until they’re locked into place, and vitamin C is what locks them. Without it, the collagen never sets, and a serious shortage shows up as bleeding gums and wounds that won’t close.¹·²

Vitamin C has two smaller jobs too. It’s one of your body’s main antioxidants, neutralizing the reactive molecules that damage cells,³ and it helps you absorb iron from plant foods,¹ which is why a squeeze of lemon on a spinach salad does more than add flavor.

That collagen role is why vitamin C turns up in so many skin formulas, ours included. In our Skin Brightening Complex it sits alongside NAC, there to help with the framework of collagen.

The Cold Myth

Now the reason most people buy it. Vitamin C and the common cold.

The largest review of the evidence pooled 29 trials and more than 11,000 people,⁴ and the headline is blunt: taking vitamin C regularly did not stop people catching colds. Popping a big dose once you already feel one coming did nothing measurable either. That’s the part the marketing gets backwards.

What it did do, taken every day, was make colds a little shorter, by around 8 percent in adults. Real, but small, a cold of seven days trimmed by half a day.

There’s one exception worth naming. In people under heavy physical strain, marathon runners, skiers, soldiers training in the cold, regular vitamin C cut their chance of catching a cold roughly in half. For everyone else going about a normal day, that protection doesn’t show up.

How Much You Need

So how much do you need? Less than the big bottles suggest. The daily target is about 90 mg for men and 75 mg for women,⁵ and you can hit that from food without trying. One orange gets you most of the way, and a single red bell pepper puts you over the line on its own.

The reason the giant doses are mostly wasted comes down to how your body handles it. Vitamin C is water-soluble, and your body only holds so much at once. Take more than it can use and the excess leaves in your urine within hours. A 1,000 mg tablet doesn’t give you ten times the benefit of 100 mg. It gives you a bit more than you can hold and a well-supplemented bathroom trip.

Past about 2,000 mg a day you can tip into the downside, mostly an upset stomach and loose bowels. There’s no prize for overshooting.

Where that Leaves You

If there’s one thing to take from all this, it’s that vitamin C matters more than the cold aisle suggests, just not in the way it’s sold. Its real job is unglamorous: it helps your body build and repair itself, day after day, mostly without you noticing.

That’s the part worth holding onto. And it’s rarely the whole story on its own. Vitamin C is one piece of how your skin stays healthy as the years add up, working next to the other things like NAC and glutathione that your body leans on to protect and rebuild itself.

If you want to see how those pieces fit together, we get into that in [Collagen, Glutathione, NAD+: Supporting Your Skin From the Inside Out].

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

References

Bisht S, Sina RE, Patel P. Vitamin C (ascorbic acid). In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2026. PMID 29763052.
Pullar JM, Carr AC, Vissers MCM. The roles of vitamin C in skin health. Nutrients. 2017;9(8):866. doi:10.3390/nu9080866.
Carr AC, Maggini S. Vitamin C and immune function. Nutrients. 2017;9(11):1211. doi:10.3390/nu9111211.
Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013;(1):CD000980. doi:10.1002/14651858.CD000980.pub4.
Office of Dietary Supplements, National Institutes of Health. Vitamin C — Fact Sheet for Health Professionals. ods.od.nih.gov.

Share

Quick FAQ

Amy Qin, PhD, RD, CDCES, Nutrition Scientist at Neumina

Amy Qin is a Nutrition Scientist at Neumina with training in both nutrition research and clinical care. She received her PhD in Nutrition and Metabolism from the University of Wisconsin-Madison and completed clinical training at Stanford Hospital and UCSF Benioff Children's Hospital.

Her work focuses on applying nutrition science to metabolism, aging, and chronic disease management in ways that are practical and personalized.