Table 4.

Summary of key and recent in vivo studies providing evidence of vitamin C effects in the skin.

Study Description	Measured Parameters	Outcome and Comment	References
Animal Studies
Oral Supplementation
Dietary supplementation of pregnant female rats. Addition of 1.25 mg/mL vitamin C to drinking water for duration of gestation.	Monitored collagen and elastin content of uterosacral ligaments by histology staining and subjective assessment.	Increased collagen production in vit.- C-supplemented rats, decreased elastin loss. Implied prevention of pelvic organ prolapse and stress urinary incontinence.	[183]
Wound healing in guinea pigs following supplementation with moderate and high-dose vit. C.	Dorsal wound healing rate and strength of repair monitored.	Increased vit. C associated with faster wound recovery and strength of skin integrity. Small sample size limited stats.	[184]
Topical application
Topical application of vit. C and vit. E-containing cream to nude mice, followed by UV irradiation.	Measured melanocyte differentiation post-irradiation. Change of skin colour—tanning, inflammation.	UVR-induced proliferation and melanogenesis of melanocytes were reduced by vit. C and E. Melanocyte population and confluence reduced when vit. C present.	[185]
Cultured skin—human keratinocytes and fibroblasts attached to collagen-glycosamino-glycan substrates, incubated for five weeks ± 0.1 mM vit. C, and then grafted to athymic mice.	Collagen IV, collagen VII and laminin 5 synthesis, epidermal barrier formation and skin graft take in athymic nude mice.	Increased cell viability and basement membrane development in vitro, better graft ability in vivo.	[157]
Human Studies
Oral supplementation
90-day oral supplementation with a fermented papaya preparation or an antioxidant cocktail (10 mg trans-resveratrol, 60 μg selenium, 10 mg vitamin E, 50 mg vitamin C) in 60 healthy non-smoker males and females aged 40–65 years, all with clinical signs of skin aging.	Skin surface, brown spots, skin evenness, skin moisture, elasticity (face), lipid peroxidation, superoxide dismutase levels, nitric oxide (NO) generation, and the expression levels of key genes (outer forearm sample).	Improved skin elasticity, moisture and antioxidant capacity with both fermented papaya and antioxidant cocktail. Increased effect of papaya extract and on gene expression. No baseline measures in study population. Antioxidant components of the fermented papaya unknown and direct link with vit. C not available.	[135]
Intervention with 47 men aged 30–45 given oral supplement of 54 mg or 22 mg of vit. C, 28 mg tomato extract, 27 mg grape seed extract, 210 mg of marine complex, 4 mg zinc gluconate for 180 days.	Subjective assessment of appearance and objective measures of collagen and elastin (histology and measurement in biopsy material).	Improvement in erythema, hydration, radiance, and overall appearance. Decreased intensity of general skin spots, UV spots, and brown spots, improved skin texture and appearance of pores. Increased collagen (43%–57%) and elastin (20%–31%).	[49]
Supplementation of 33 healthy men and women (aged 22–50), with placebo, 100 mg vit. C or 180 mg vit. C daily for four weeks.	EPR measurement of TEMPO scavenging in skin on arm. Raman resonance spectroscopy for skin carotenoids.	Improved oxygen radical scavenging with vit. C supplementation, dose dependency indicated and rapid response (obvious within two weeks).	[38]
Three month supplementation of 12 males and six females (21–77 y) with 2 g vit. C and 1000 IU D-alpha-tocopherol.	Measured blood vitamin levels before and after, skin resilience to UVB, detection of DNA crosslinks in skin biopsy.	Serum vit. C and vit. E doubled during intervention (implies sub-saturation at baseline). Minimal erythema dose increased with supplementation, DNA damage halved.	[20]
Investigation of antioxidant capacity in human skin before and after UV irradiation; effect of supplementation with 500 mg vit. C per day.	Measurement of erythema and antioxidant levels following UVB irradiation.	Vit. C and E levels increased, but levels not realistic (plasma vit. C 21 µM before and 26 µM after 500 mg daily). Skin MDA and glutathione content lowered, no effect on MED.	[27]
Topical application
Topical application of vit. C cream in advance of application of hair dye product p-phenylenediamine.	Visual assessment of allergic reaction following patch application on volunteer skin (on back).	Decreased or ablation of dermatitis and allergic response due to local antioxidant action of vit. C in cream.	[170]
Clinical study applying vit. C in liposomes to human skin (abdomen), then exposure to UV irradiation.	Measured penetration through skin layers, delivery of vit. C, loss of Trolox, TNFalpha and Il-1beta.	Increased vit. C levels in epidermis and dermis with liposomes. Protection against UV increased over liposomes alone.	[67]
Microneedle skin patches to deliver vit. C into the skin assessed on areas of slight wrinkle formation (around eyes).	Global Photodamage Score by visual inspection. Skin replica analysis and skin assessment by visiometer.	Slightly improved photodamage score and lessening of wrinkles after 12 weeks of treatment with vit. C-loaded patches.	[186]
Vit. C-based solution containing Rosa moschata oil rich in vitamins A, C, E, essential fatty acids /placebo moisturizer cream applied to facial skin of 60 healthy female subjects for 40–60 days.	Ultrasound monitoring thickness of the epidermis and dermis, and low (LEP), medium (MEP), high echogenic pixels (HEP), reflecting hydration, inflammatory processes, elastin and collagen degeneration (LEP), and structure of collagen, elastin and microfibrils (MEP and LEP).	Data suggest epidermis but not the dermis increased in thickness. Increase in MEP and HEP (collagen and elastin synthesis) and decreased LEP (inflammation and collagen degeneration). No vit. C status measurements in skin of individuals.	[149]
In vivo study with 30 healthy adults. Protective effect of SPF30 sunscreen with and without anti-oxidants (vit. E, grape seed extract, ubiquinone and vit. C) against Infra-Red A irradiation on previously unexposed skin (buttock).	Skin biopsy analysis; mRNA and RT-PCR for matrix metalloprotein-1 (MMP-1) expression 24 h post irradiation.	Sunscreen plus antioxidants protected skin against MMP-1 increase, sunscreen alone did not. No indication of levels of antioxidants, or whether they were able to penetrate into skin layers. Multi-component antioxidant mix.	[153]
In vivo study of 15 healthy adults. Protective effect of vitamin C mixtures (vit. C, vit. E, ferulic acid OR vitamin C, phoretin, ferulic acid) on ozone exposure on forearms.	Skin biopsy analysis; 4-HNE and 8-iso prostaglandin levels, immunofluorescence for NF-kB p65, cyclooxygenase-2, matrix metalloprotein-9 (MMP-9), type III collagen. After 5 days of 0.8 ppm ozone for 3h/d.	Vitamin C mixture reduced ozone induced elevation in lipid peroxidation products, NF-kB p65, cyclooxygenase-2 expression and completely prevented MMP-9 induction by ozone. No indication of levels of antioxidants, or whether they were able to penetrate into skin layers. Multi-component antioxidant mix.	[187]
Test of topical silicone gel with vit. C on scar formation in a population of 80 Asian people. Gel applied for six months after operation.	Scar formation monitored by modified Vancouver Scar Scale (VSS) as well as erythema and melanin indices by spectrophotometer.	Vit. C decreased scar elevation and erythema, decreased melanin index. Improved wound healing (stitch removal).	[166]