Vitamin C Research
A 2012 meta analysis on two double-blind, randomized, placebo-controlled trials found that “Vitamin C plus Zinc was significantly more efficient than placebo at reducing rhinorrhoea (runny nose)” 
The Journal of Nutrition & Metabolism published an 8-week study on young adults showing that “low Vitamin C status is associated with reduced fat oxidation”. It provided proof that a Vitamin C deficiency can hinder healthy weight loss. 
When reviewing 15 independent studies with a total of 1,360 participants, researchers found that “zinc administered within 24 hours of onset of symptoms reduces the duration and severity of the common cold in healthy people.” and “When supplemented for at least 5 months, it reduces cold incidence”. 
The Journal of Investigative Dermatology found that ascorbic acid [Vitamin C] could increase the rate of collagen production in a variety of age groups, as well as being capable of “overcoming the reduced proliferative capacity of elderly dermal fibroblasts”.  It can also significantly increase the rate of overall collagen production, without interfering with the production of precollagen mRNAs. 
High dietary intake of vitamin C is associated with notably lower incidences of common chronic diseases, “including heart disease, cancer, eye diseases, and neurodegenerative conditions”, and “the evidence that ascorbic acid acts as an important antioxidant in many body tissues is convincing”. 
In a meta-analysis of five controlled trials, Vitamin C administered prior to exercise led to a 48% reduction in symptoms of exercise-induced bronchoconstriction (tightness in the chest and difficulty breathing). 
A study of 3640 older adults with age-related macular degeneration found a “statistically significant odds reduction for the development of advanced AMD with antioxidants [Vitamin C & Vitamin E] plus zinc”. 
Vitamin C is potentially protective against UVB sun damage to skin cells , and is involved in the reduction of inflammatory cytokines in UVA damaged keratinocytes (outer skin cells) .
Vitamin C is also positively correlated with faster cell repair in skin lesions. “Cells exposed to AA2P (ascorbic acid) increased the expression of genes associated with DNA replication and repair… vitamin C may protect the skin by promoting fibroblast proliferation, migration, and replication-associated base excision repair of potentially mutagenic DNA lesions.” Resources
- A combination of high-dose vitamin C plus zinc for the common cold.
- Marginal vitamin C status is associated with reduced fat oxidation during submaximal exercise in young adults.
- Zinc for the common cold.
- Effects of ascorbic acid on proliferation and collagen synthesis in relation to the donor age of human dermal fibroblasts.
- Ascorbic acid specifically increases type I and type III procollagen messenger RNA levels in human skin fibroblast.
- Vitamin C function and status in chronic disease.
- Vitamin C may alleviate exercise-induced bronchoconstriction: a meta-analysis.
- Age-Related Eye Disease Study Research Group. A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, beta carotene, and zinc for age-related macular degeneration and vision loss: AREDS report no. 8.
- Antioxidant nutrients protect against UVB-induced oxidative damage to DNA of mouse keratinocytes in culture.
- L-ascorbic acid inhibits UVA-induced lipid peroxidation and secretion of IL-1alpha and IL-6 in cultured human keratinocytes in vitro.
- Gene expression profiling reveals new protective roles for vitamin C in human skin cells.