Here are a bunch of studies about the effects of dietary carotenoids on photoaging prevention:
Note: Very good article documenting the studies proving and explaining the role of carotenoids in skin photoprotection.
Conclusion: Meta-analysis of 7 studies testing the effect of dietary/oral beta-carotene supplementation on sunburn protection concluded that high intake of beta-carotene does indeed improve UV tolerance, however this practice must be consistent and long-term (at least 10 weeks) before any positive results are observed.
Supplementation with β-Carotene or a Similar Amount of Mixed Carotenoids Protects Humans from UV-Induced Erythema (2003)
Conclusion: 36 white people were split into three groups and given either a high-dose beta-carotene supplement, carotenoid-complex supplement, or a placebo for 3 months. They were exposed to a UV light at baseline, 6 weeks, and at the end of the study to measure for changes in erythema (sunburn) response. Both the beta-carotene group and carotenoid-complex group enjoyed a reduced sunburn response compared to the placebo group and this effect improved over the course of the study.
Conclusion: Cross-sectional study evaluated 22 white people for their skin carotenoid levels and MED (minimal erythemal dose, aka sunburn tolerance) and found a positive correlation between higher skin carotenoid levels and improved UV tolerance.
Carotenoids and Carotenoids Plus Vitamin E Protect Against Ultraviolet Light-Induced Erythema in Humans.(2000)
Conclusion: Study testing ability of supplemental carotenoids and vitamin E on sunburn prevention. Volunteers were given for 12 weeks either a carotenoid supplement or a carotenoid + vitamin E supplement. They were exposed to UV light adequate to induce sunburn throughout the study to measure changes in erythema response. After 8 weeks of supplementing sunburn responses were reduced and carotenoids + vitamin E combined was found to be most effective.
Conclusion: Randomized control trial compared the effects of two different dietary antioxidant complex supplements (different amounts of beta-carotene, lycopene, vitamin E, and vitamin C) on the melanin responses to UV in 20 healthy white subjects. Participants were split to take either of the supplements daily for 8 weeks and their melanin responses were evaluated throughout the study. Both groups enjoyed increased melanin responses at 4, 5, 6, and 8 weeks into the study as measured with multiple reflection spectrometry. Get those antioxidants.
A CLINICAL TRIAL OF THE EFFECTS OF ORAL BETA-CAROTENE ON THE RESPONSES OF HUMAN SKIN TO SOLAR RADIATION (1972)
Conclusion: Randomized control trial had 30 white male prison inmates take either an oral high-dose beta-carotene supplement or placebo daily for 10 weeks and measured changes in their UV tolerance (minimal erythemal dose – sunburn response). The beta-carotene group enjoyed a small increase in their MED.
Also see photoaging studies on