People swear that popping a few vitamin C tablets when their throat starts to feel sore is a surefire method to prevent a cold.
Unfortunately, evidence doesn't support that. At the very best, daily supplementation with vitamin C (i.e., every single day, not just the day before you feel sick) may reduce the duration of a cold. A Cochrane review found that adults experienced 8% and children 14% fewer sick days when they took vitamin C every day. In other words, if the average adult is sick 10 days per year, supplementing with vitamin C would reduce it to 9 days. The review further concluded that "routine mega-dose prophylaxis is not rationally justified."
Echinacea doesn't work, either. Can anything reduce our misery? Yes, zinc might.
A team of researchers performed a meta-analysis on three small randomized trials. Combined, the analysis examined 102 participants taking zinc and 97 taking placebo. The same team members had analyzed the data before and found that zinc was helpful for reducing cold duration, but they weren't quite satisfied with their statistical methods. So, they tried what they believed to be a superior method (known as Cox regression) and recrunched the numbers.
The data curve (shown on the right) suggests that zinc may be even more beneficial than they previously estimated. By Day 5, 70% of people taking zinc lozenges had recovered from the common cold, compared to only 27% of people taking placebo.
That's a ratio of 2.6, which is similar to the ratio provided by their Cox regression analysis (which is 3). Thus, the authors concluded that zinc lozenges may triple the recovery rate for people suffering from the common cold.
The best part is that daily supplementation isn't necessary. When you feel a cold coming on, start popping zinc lozenges. That will do much more for you than vitamin C or Echinacea.
While zinc isn't a cure for the common cold, it may be the closest we can get. At least for now.
Source: Harri Hemilä, James T. Fitzgerald, Edward J. Petrus, Ananda Prasad. "Zinc Acetate Lozenges May Improve the Recovery Rate of Common Cold Patients: An Individual Patient Data Meta-Analysis." Open Forum Infectious Diseases 4 (2). Published: Spring 2017. doi: 10.1093/ofid/ofx059