The common cold can be mild to down right nasty, causing you put everything on hold and rest up. It's estimated that the common cold causes 23 million lost days of work each year. But how does this happen?
A cold virus typically enters your body through your mouth, eyes or nose and is spread from virus containing droplets in the air, or from being in close proximity of someone who is sick and touching or being touched directly by the virus. Once the nose and throat are infected it may take anywhere from one to three days before you notice the uncomfortable sore throat, nasal congestion, runny nose, coughing, sneezing, low-grade fever, mild headache, and slight body aches that begin to kick in. There are over 200 different types of viruses that cause the common cold with the most common type being the rhinovirus.
Many of us take more precautions during "cold and flu" season, but we are still susceptible to colds any time of year (1). If you've ever caught a summer cold you're well aware. So what can you do to prevent a week of misery? You've probably heard that vitamin C is a common remedy for colds but does it actually work? We're going to take a deep dive on the research and see what the scientific consensus says.
Our bodies don't make vitamin C, but we need it for immune function, bone structure, iron absorption, and healthy skin. We get vitamin C from our diet, usually in citrus fruits, strawberries, green vegetables, and tomatoes. The Recommended Dietary Allowance for men is 90 milligrams (mg) per day, and for women, it's 75 mg per day (2).
When it comes to vitamin C there have been a lot of high quality studies (placebo-controlled trials) that have looked at the effects of vitamin C supplements on the prevention and treatment of colds.
Back in 1979 a study published in JAMA took a group of 674 marine recruits and gave about half of them 2g/day of a vitamin C supplement over the course of 8 weeks to see if it would prevent the common cold. The marine recruits were randomly chosen to be given either a placebo or the vitamin C supplement. The scientists and recruits both had no idea who had received the supplement until after the study, in order to control for a placebo effect. In the recruits who got sick there was no difference between the groups in the duration of the cold. But in those who received the vitamin C scientists found whole-blood ascorbic acid levels much higher, less severe colds and found less recruits got sick overall in the vitamin C group, although the differences weren't statistically significant (3).
A 2011 study published in the European Journal of Pediatrics researchers looked at 39 teenage swimmers in Jerusalem, Israel who were given 1g/day of a vitamin C supplement to see if it affected the rate, length, or severity of their colds. This randomized, double-blind, placebo-controlled trial found that vitamin C cut the duration of the colds by 22% in both male and female swimmers, and cut the duration of colds by 47% in male swimmers. Vitamin C also appeared to reduce the severity of symptoms in both males and females but worked better in male swimmers compared to the female swimmers. Overall vitamin C didn't appear to prevent colds in either group (4).
A gold standard review study published in 2013 in the Cochrane Reviews looked to bring the vitamin C controversy to rest by performing the largest review to date on vitamin C and the common cold. The authors combined past studies that were similar in treatments and outcome measures. One of the first combinations of studies looked at 29 controlled trials and over 11,000 patients who took vitamin C, at recommended daily amounts, and found no prevention of the common cold. The authors also combined of 31 controlled trials that looked at over 9,745 patients, and found that regular supplementation did have a modest and consistent effect in reducing the duration of common cold symptoms. When the authors combined 5 controlled trials looking at those undergoing intense physical activity; including marathon runners, cross country skiers, or soldiers in subarctic conditions, vitamin C cut the incidence and duration of colds in half with no side effects. The authors also looked at higher dose vitamin C supplements (1-8g/day) and they concluded that it didn't appear to offer additional benefits once the cold had started. In all of adult and children studies combined, adults reduced the duration of their colds by 8% and children by 14% (5). Overall, the research looks supportive at reducing the duration and severity of colds in children and adults, and especially positive in reducing cold severity and duration in those in extreme environmental conditions and undergoing intense physical activity.
Another more recent but smaller review published in 2018 in BioMed Research Intl. combined 9 human placebo-controlled trials and found that additional doses of vitamin C beyond the normal daily value (+1-2g/day) is recommended, as this amount was shown to reduce the symptoms and severity of a cold (6).
A 2017 review study published in Nutrients looked at the benefits of vitamin C beyond just the common cold and was found to be effective for a wide variety of infections. In fact vitamin C deficiency was found to be positively associated with pneumonia. A total of 148 animal studies indicated that vitamin C may alleviate or prevent infections caused by bacteria, viruses, and protozoa. Three human controlled trials found that vitamin C prevented pneumonia. Two controlled trials found a treatment benefit of vitamin C for pneumonia patients. One controlled trial reported treatment benefits for tetanus patients (7). The effects of vitamin C for infections in general definitely warrants that more research should be done at higher doses of 1-2g/day or higher.
The bottom line is that a vitamin C supplement is a great cost-effective option for those undergoing physical, environmental, and emotional stress, and those with potentially weaker immune systems looking to reduce the severity and duration of a cold. Prevention appears to be key when it comes to a cold, because supplementing with the RDA of vitamin C hasn't shown to reduce the risk of catching a cold. Supplementing with vitamin C however may speed up your recovery from a cold and reduce the severity of your symptoms if taken consistently. Doses of an additional 500-2,000 mg/day is a good place to start to prevent colds, especially during times of high stress, high physical intensity, when you're around sick individuals and more people in general such as holiday gatherings and when traveling. Look for a product from a high quality supplier.
1. Mayo Clinic Staff. (2019). Common cold - Symptoms and causes. Retrieved 26 December 2019, from https://www.mayoclinic.org/diseases-conditions/common-cold/symptoms-causes/syc-20351605
2. Office of Dietary Supplements - Vitamin C. (2019). Retrieved 26 December 2019, from https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/
3. H. A. Pitt and A. M. Costrini, “Vitamin C Prophylaxis in Marine Recruits,” Journal of the American Medical Association, vol. 241, no. 9, pp. 908–911, 1979.
4. N. W. Constantini, G. Dubnov-Raz, B.-B. Eyal, E. M. Berry, A. H. Cohen, and H. Hemilä, “The effect of vitamin C on upper respiratory infections in adolescent swimmers: A randomized trial,” European Journal of Pediatrics, vol. 170, no. 1, pp. 59–63, 2011.
5. Hemilä, H., & Chalker, E. (2013). Vitamin C for preventing and treating the common cold. Cochrane Database Of Systematic Reviews, Jan 31;(1). doi: 10.1002/14651858.cd000980.pub4
6. Ran, L., Zhao, W., Wang, J., Wang, H., Zhao, Y., Tseng, Y., & Bu, H. (2018). Extra Dose of Vitamin C Based on a Daily Supplementation Shortens the Common Cold: A Meta-Analysis of 9 Randomized Controlled Trials. Biomed Research International, 2018, 1-12. doi: 10.1155/2018/1837634
7. Hemilä, H. (2017). Vitamin C and Infections. Nutrients, 9(4), 339. doi: 10.3390/nu9040339