[pdf 2008] Vitamin C: Evidence, application and commentary.  Melissa et al.  Vitamin C has a critical role to play in the prevention and intervention of many medical conditions. There is scientific evidence supporting the use of vitamin C during acute and chronic illnesses, for injuries, and for reducing the risk of disease. The safety of vitamin C over a wide range of doses has been demonstrated in a number of clinical trials; reports of serious adverse events are very rare. As a safe, natural, low-cost nutrient, the potential immune-supporting and antioxidant benefits of vitamin C should be considered when developing treatment plans.

[1999] Gorton et al. The effectiveness of vitamin C in preventing and relieving the symptoms of virus-induced respiratory infections

[pdf] H. Hemilä, et al. Vitamin C and acute respiratory infections  From the studies published so far it is evident that in large doses vitamin C has distinct but modest therapeutic effects on the severity and duration of the common cold, even in well nourished populations. There are also possible benefits in the prevention of acute respiratory infections, especially in populations that are malnourished or physically stressed. It is our view that three widely cited reviews concluding that vitamin C had little if any effect on the common cold did not accurately represent data from the original publications. For example, data inconsistent with the original study reports were presented, several highly relevant findings were overlooked, and data were analysed inappropriately. Furthermore, the authors of the most influential trial so far concluded that the difference between the vitamin C and placebo groups was paradoxically caused by the placebo effect. The placebo effect interpretation of the results was, however, recently shown to be erroneous, indicating that the observed benefit was indeed caused by the physiological effects of the vitamin.

[1994 pdf] Hunt et al. The Clinical Effects of Vitamin C Supplementation in Elderly Hospitalised Patients with Acute Respiratory Infections  Although this study was performed on a relatively small number of subjects the results suggest that moderate vitamin C supplementation could have clinical benefit to patients suffering from acute respiratory infection, particularly to those who are most severely ill on admission. In many of these patients, plasma and white cell vitamin C levels are likely to be low enough to be construed as representing at least marginal deficiency, but 200 mg per day boosts these considerably within 2 weeks. Conversely, in the un-supplemented patients', concentrations of the vitamin remain low. These results are therefore consistent with evidence that vitamin C assists immune function possibly by acting as an anti-oxidant.