Its that time of year again...
If you've been an elevator recently with someone sniffling, you're probably doing everything you can to avoid catching a cold. We often get asked in our office whether or not it's worth it to take vitamin C supplements or eat vitamin C rich foods in an effort to reduce cold infections or their duration. We'll address our stance in this blog.

Let's start by clarifying what vitamin C (ascorbic acid) is--it is essentially a potent antioxidant. It helps neutralize free radicals, supports immune cell function (e.g. neutrophils, lymphocytes), regenerates other antioxidants, and is involved in collagen synthesis, which helps maintain mucosal barriers. These functions mean vitamin C can modulate inflammation — which is one of the key components of the body’s response to viral infection like the common cold.

Supplemental Vitamin C: Trials & What They Find

• A large recent meta‑analysis (BMC Public Health, 2023) found that regular doses of ≥1 g/day of vitamin C (supplements) significantly reduced the severity of common cold symptoms by about 15% compared with placebo. The effect was larger for severe stages/symptoms than for mild colds¹
  

• The Cochrane review “Vitamin C for preventing and treating the common cold” shows that regular supplementation does not significantly lower the risk of getting a cold in the general population (ordinary people), but does modestly reduce the duration of colds. In trials with people under physical stress (runners, skiers, soldiers) vitamin C prophylaxis halved the risk of catching a cold²

• In a randomized controlled trial in Japan (Akita Prefecture), comparing 50 mg vs 500 mg daily vitamin C over 5 years, the higher dose group had significantly fewer colds (per 1,000 person‑months: 21.3 vs 17.1), and fewer people catching colds 3+ times, but no clear effect on cold severity or length³

Deciding Whether to Get Vitamin C From Food or Supplements is Tricky

• There is less random control trials (i.e. really strong evidence) comparing getting vitamin C from foods vs supplements specifically in cold/inflammation studies. Much of the data is observational or cohort studies, which often show that higher intake of fruit & vegetables (which include vitamin C but also other nutrients & phytochemicals) correlates with lower markers of inflammation, improved immune responses, etc. However, these studies are less able to isolate vitamin C alone.

• One cohort (Spanish university staff, ~4,272 people) looked at baseline vitamin C and zinc from diet and found no significant relationship between total vitamin C intake from food + diet and the incidence of colds⁴

How much shortening / speeding recovery?

• The meta‑analysis (≥1 g/day supplement) showed that vitamin C reduces the severity of colds by ~15%, and for more severe colds the reduction in duration can be larger

• The “extra therapeutic doses” meta‑analysis (before retraction notices aside) suggested modest benefit: reduction in cold duration by about half a day on average; reduced days confined indoors by ~10 hours.

Is supplementing worthwhile (Emergen‑C, plain tablets, gummies, etc)?

Pros:

• If you're not getting enough vitamin C in your diet (low fruit/veg intake), supplements can help you reach the RDA and perhaps more, which may help reduce severity / shorten colds somewhat.

• For certain groups exposed to physical stress, cold climates, or heavy training, studies show more pronounced prophylactic benefit. Runners, skiers, soldiers: risk of catching cold reduced ≈ 50% with vitamin C supplements

• When a cold begins, increasing vitamin C may modestly speed recovery / reduce worst symptoms (but doesn’t cure).

Cons / caveats:

• Most trials show that vitamin C does not prevent colds in general population if you already have adequate intake.

• High doses can be expensive, and excess vitamin C beyond what your body can use is excreted (water soluble). Very high intakes can cause GI upset, maybe increase risk of kidney stones in susceptible individuals.

• Over-the‑counter products like Emergen‑C often come with large doses (e.g. 1,000 mg or more) plus sugars or electrolytes; may be overkill if you already eat fruit/veg regularly.

Conclusion:

Yes, supplementing your diet with vitamin C can be worth it if you have low baseline intake, are under physical or environmental stress, or want to reduce severity of a cold. But for most people with reasonably good diet, a modest supplement or just ensuring enough foods may be sufficient. It’s not a guaranteed shield, and mega‑doses don’t seem to offer huge extra benefit beyond a certain point.

Getting Vitamin C from Diet: How Much Do You Need?

The RDA for vitamin C in healthy adults is roughly 75 mg/day for women, 90 mg/day for men.

Here are three foods you can use (raw or lightly cooked) to reach ~100% of an adult RDA, with suggested meals or pairings to improve absorption (vitamin C also helps iron absorption, so pairing with iron‑rich foods is useful; fat doesn’t really affect vitamin C, but raw/cold preserves the vitamin better).

Also note: to preserve vitamin C, eat raw or lightly cooked (steaming briefly rather than long boiling), avoid long storage or exposure to heat/light. Pairing vitamin C‑rich foods with iron sources (plant iron, meat) boosts non‑heme iron absorption. Eating them with fats doesn’t hurt but isn’t necessary for absorption of vitamin C itself.

Bottom‑line: What should you do?

• First, assess your dietary habits. If you eat a lot of fruits & vegetables regularly (raw peppers, citrus, berries, broccoli, etc.), you’re probably getting enough or near enough vitamin C.

• If you tend toward minimal fruit/veg, or under stress (cold weather, workouts, travel), a moderate supplement (e.g. 500‑1,000 mg) might help reduce cold severity and speed up recovery. Discuss this with your physician before taking. Some populations have increased risk of kidney stones with vitamin C intakes. 

• Don’t assume big doses cure colds or prevent them in all cases; they help modestly. Over‑consuming isn’t always beneficial and may have side effects.

References:

1.Hemilä, H., Chalker, E. Vitamin C reduces the severity of common colds: a meta-analysis.BMC Public Health 23, 2468 (2023). https://doi.org/10.1186/s12889-023-17229-8

2.Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews 2013, Issue 1. Art. No.: CD000980. DOI: 10.1002/14651858.CD000980.pub4.

3. Eur Clin Journal.2006 Jan;60(1):9-17.doi: 10.1038/sj.ejcn.1602261.

4. Epidemiology.2002 Jan;13(1):38-44. doi: 10.1097/00001648-200201000-00007.