For decades we have been trying to understand the effects of vitamin C on the immune system. Linus Pauling wrote Vitamin C and the Common Cold in 1970, and sometimes it feels like we haven’t made any progress. The best and most comprehensive analysis of the data at hand, collected from decades of research studies, shows that vitamin C has effects on the common cold – but they are very limited in the general population.
This has led many to conclude that taking vitamin C to ward off a cold just isn’t worth it.
So is this the final word on the subject?
Hundreds of thousands of people, if not millions, take vitamin C to support their immune function. Anecdotal reports from around the globe have attested to the impact of vitamin C supplementation on health. Are people just fooling themselves? Why can’t the scientific evidence give us a definitive answer?
To put in bluntly: vitamin C studies have been a large mess of dirty data. Despite many decades trying to get it right, scientists still are doing a terrible job.
Vitamin C research has evolved very slowly over the 80 years since the vitamin was discovered. Scientists have yet to develop successful ways of studying many micronutrients, and vitamin C presents a special challenge due. Unfortunately, as the scientists at the LPI recently discussed, many studies on vitamin C are not well designed and hard to interpret. Trying to tie all those studies together is often impossible… and even when you do find a way to do it, the conclusions are weak.
So instead of relying on the past, is it time to rethink vitamin C from the ground up, especially with studies on the common cold? Maybe vitamin C deserves a restart, so to speak.
Where does this begin? Just like every new beginning, researchers need to learn from their mistakes.
If you look for it, it is not difficult to see where vitamin C studies fall short. It sounds like a simple task, but astoundingly few studies actually look for changes in blood levels of the vitamin when giving someone a supplement. It not only goes against best practices to assume that vitamin C levels will change, the evidence shows that many factors can influence the response to supplements – people are not all the same.
For example, a recent study by Carol Johnston PhD and her colleagues recruited 28 healthy, non-smoking, young men and measured the vitamin C levels in their blood. At the beginning of the study, half of the subjects were randomized to a group that received 1,000 mg of vitamin C each day, while the other half received a placebo pill.
At the onset of the study, plasma levels of vitamin C were measured each week in each subject. After the first week of supplementation there was no difference in vitamin C levels between the two groups. If the study had terminated after one week, in fact, the conclusion would have been that supplements do nothing to change vitamin C levels in the body.
But the study continues, and although it increased slowly, within four weeks vitamin C levels increased in all men taking the supplements (but not in those who took the placebo).
Now here comes the really interesting part. This study was actually a study on vitamin C and the common cold. By the end of the eight-week study, the men taking vitamin C had fewer colds versus those taking the placebo, suggesting that raising vitamin C levels in the body was very important in preventing a cold from developing. The men taking vitamin C who did get a cold tended to have fewer days with symptoms and shortening their colds by about three days, but unfortunately those results did not reach statistical significance compared to those getting the placebo.
Those taking vitamin C supplements were also more physically active, but that is possibly because they were feeling better (less cold symptoms), but other possibilities exist: vitamin C has been shown to affect mood and energy metabolism.
This was a remarkable finding and perhaps signals a new beginning for research on vitamin C and colds. However, it is just a start – this study had a small number of subjects, so many more equally well-designed studies will be needed to signal a change in consensus on C.
Overall, vitamin C research needs to be elevated to a higher quality to succeed on these important questions. A recent analysis of vitamin D supplementation in the treatment of respiratory tract infections showed that very specific criteria representing the best of nutritional science and our knowledge about the way vitamin D works in the body can produce some fascinating results. If we can do the same for vitamin C, perhaps one day its effects on the common cold may finally be revealed.