Here are some studies about vitamin C and photoaging prevention:
Note: Technical, comprehensive overview of vitamin C’s roles and functions in skin health.
Note: Comprehensive, technical overview of how vitamin C promotes skin health and photoprotection by improving skin collagen formation, removing free radicals, reversing UV-induced oxidative stress, stimulating ceramide production (the glue that binds skin cells), improving UV tolerance, and improving wound healing.
Vitamin C and Skin Health (2011)
Note: Overview of how vitamin C promotes skin health and photoprotection by reducing UV-induced oxidative stress, improving skin collagen formation, stimulating DNA repair, and working synergistically with vitamin E to increase UV tolerance.
Ultraviolet B-Induced DNA Damage in Human Epidermis Is Modified by the Antioxidants Ascorbic Acid and D-α-Tocopherol (2005)
Conclusion: Study had 18 subjects take oral vitamin C and E supplements twice-daily for three months. They’re MED (minimal erythemal dose aka sun/UV tolerance) was measured at baseline and at the end of the study. Within one week of starting the supplement regimen the participants’ MED had increased by 21%, but after three months of supplementation the MED had increased by 41%. Subjects also enjoyed a significant decrease in measurable UV-induced DNA damage.
Photoprotection of UV-Irradiated Human Skin: An Antioxidative Combination of Vitamins E and C, Carotenoids, Selenium and Proanthocyanidins (2002)
Conclusion: Randomized control trial of young women tested out an antioxidant supplement containing carotenoids, vitamin E, vitamin C, selenium, and proanthocyanidin plant polyphenols for it’s effectiveness at reducing post-UV exposure erythema (sunburn) and matrix metalloproteinases expression (enzyme responsible for skin collagen breakdown). The treatment group demonstrated slower and less-severe sunburn development compared to the placebo group and reduced expression of matrix metalloproteinases.
UVB Photoprotection with Antioxidants: Effects of Oral Therapy with d-a-Tocopherol and Ascorbic Acid on the Minimal Erythema Dose (2002)
Conclusion: Vitamin C and E have been known to individually provide photoprotective effects in skin, but it has also been found that they have a significantly more powerful effect when used synergistically. This study took 45 participants and split them into 3 different groups receiving either oral vitamin E, oral vitamin C, or vitamin C and E combined daily for one week and then measured their MED (minimal erythemal dose – amount of UV you can tolerate before burning). The study confirmed that combining vitamin C and E produces a significantly more powerful photoprotective effect than supplementing with either of them separately, as this group enjoyed the biggest increase in their MED by a lot.
Protective Effect Against Sunburn of Combined Systemic Ascorbic Acid (Vitamin C) and D-Alpha-Tocopherol (Vitamin E) (1998)
Conclusion: Randomized control trial found that supplementing with vitamin C and E together effectively increased the participants’ minimal erythemal dose (MED – the amount of sun you can get before burning) effectively increasing their UV tolerance. One group of participants were given a daily dose of 2g vitamin C combined with 1000 IU vitamin E for 8 days, while the other group were given a placebo during that time. The sunburn reaction was measured before and after. The treatment group enjoyed a measurable increase in UV tolerance, whereas the placebo group did not.