Vitamin C

Vitamin C was popular for many years for immunity, but its claims have been disputed over the last few decades. This is because vitamin C was shown over many studies to have no impact on whether you would get sick with respiratory illnesses such as the common cold.² However, positive evidence does exist for other immunity benefits, and many people, especially smokers, do not get enough vitamin C in their diet.

For background, vitamin C is an essential vitamin involved in immune system function and in the biosynthesis and metabolism of various molecules. It is also an antioxidant. The human body cannot synthesize vitamin C, so it must be ingested in your diet. Without it, scurvy develops, which involves weakness, gum disease, and bleeding.

To evaluate the impact on immunity, a systematic review of 31 trials evaluated frequency, duration, and severity of common cold symptoms. While there was no impact on whether you get sick, duration of cold symptoms decreased by 8%, and severity decreased statistically significantly as well.² This suggests that the literature supports small immunity benefits for vitamin C overall.

Furthermore, many people lack vitamin C in their diets. 93% of female smokers and 88% of male smokers don't get enough vitamin C.¹ Among non-smokers, 49% and 40% of male and female nonsmokers had vitamin C intake levels below the recommended amount. If you are a smoker or do not get enough vitamin C through your diet (i.e., through fruits and vegetables), then we recommend supplementation.