Is taking extra vitamin C worthwhile?

For the average healthy person, taking extra vitamin C has no proven effect. Large-scale research involving nearly 884,000 participants shows no benefit for preventing colds, cardiovascular disease, or type 2 diabetes.^1,2

There is one clear exception: people who exercise intensively, such as marathon runners or military recruits. In this group, daily vitamin C roughly halves the number of colds. For people with an ordinary, lightly active lifestyle, this benefit does not apply.

If you take vitamin C daily and still catch a cold, it does help somewhat. Fifteen studies with a combined total of more than 6,000 participants show that symptoms are on average 15% less severe. Higher doses of 6 to 8 grams per day appear to shorten the duration of a cold more than lower doses of 3 to 4 grams. Researchers say it is reasonable to try this for yourself, but it is not a firm recommendation. Starting once you are already ill does not demonstrably help; the studies contradict each other on this point.^3,4

For memory and cognition, the evidence is extremely thin. A combination of low doses of vitamin C with vitamin E produced no improvement. Higher doses of vitamin C on its own occasionally showed positive signals, but this is insufficient to recommend supplementation.⁵

More is not automatically better, by the way. Under certain circumstances, vitamin C can also cause oxidative damage rather than protect against it. One group does have a genuine reason to supplement: people who eat only animal products. They are likely to get too little vitamin C from their diet. With a normal, varied diet you get enough, and taking extra then offers little benefit, unless you exercise intensively.⁶