Summary:
This study investigated how dietary vitamin C affects human skin vitamin C levels and skin structure. It was a controlled intervention study conducted across healthy adults, designed to measure vitamin C (ascorbate) concentrations in different skin layers and link those to skin outcomes. Researchers first quantified baseline ascorbate levels in the dermis and the epidermis, finding that dermal fibroblasts contained substantially higher concentrations than epidermal keratinocytes. Plasma vitamin C levels were tightly correlated with ascorbate levels in both skin compartments. In the dietary intervention arm, participants consumed approximately 250 mg of vitamin C daily through kiwifruit for several weeks. Plasma vitamin C increased to saturation levels in individuals with lower baseline status, and this rise was reflected in elevated skin ascorbate concentrations in both dermal and epidermal tissues. Other objective measures showed that skin density increased following supplementation, indicating stronger dermal structural protein content. There was also increased epidermal cell proliferation, suggesting enhanced skin renewal. However, skin elasticity decreased slightly and UVA-induced oxidative protection did not show measurable improvement over the study period. These findings demonstrate that oral vitamin C intake elevates ascorbate within key skin layers and positively affects structural indicators such as dermal density and epidermal turnover. The results support the concept that maintaining sufficient systemic vitamin C can influence skin biology.
Abstract:
Vitamin C (ascorbate) is found in all skin compartments. In vitro studies have indicated that it promotes collagen synthesis by fibroblasts, scavenges UVR-generated radicals, and stimulates keratinocyte proliferation and differentiation (Pullar et al, 2017; Sato et al, 2025; Wang et al, 2018). It is therefore assumed that boosting skin ascorbate levels will improve skin health and reverse the visible effects of aging. To this end, much attention is given to the topical application of ascorbate and to developing formulations to increase its stability in solution and penetration through the impermeable stratum corneum (reviewed in Enescu et al [2022]). However, in vivo delivery of ascorbate to the skin is tightly regulated by active transport from the plasma through the sodium-dependent vitamin C cotransporters SVCT1 and SVCT2 (Lykkesfeldt et al, 2025; Steiling et al, 2007). Numerous nutritional intervention studies have monitored the effect of oral ascorbate intake on skin function (reviewed in Bertuccelli et al [2016] and Pullar et al [2017]) but without measurement of skin ascorbate content. Only one study has measured skin ascorbate after ascorbate supplementation (McArdle et al, 2002), and no studies have measured skin ascorbate content in association with disease states or with skin functions. We have undertaken a comprehensive investigation to establish the relationship between plasma and skin ascorbate levels, with a focus on the major skin compartments. Skin tissue is predominantly dermis, which is mostly collagen bundles with fewer cells, with a very thin cellular epidermal layer (Figure 1a). In a cross-sectional study using skin and blood samples from healthy individuals undergoing elective surgery (Supplementary Materials and Methods and Supplementary Table S1), we found that dermal ascorbate closely reflected whole-skin levels, whereas epidermal levels were significantly higher (epidermal:dermal ascorbate mean = 2.0, range = 0.8–7.2) (Figure 1b). Approximately 20% of the ascorbate was present as dehydroascorbate (Figure 1c), probably generated during sample processing, despite our fast handling time (<15 minutes) and stringently optimized extraction process. Dehydroascorbate is typically barely detectable in cells and plasma. Whole-skin ascorbate was strongly positively correlated with dermal and epidermal ascorbate, and there was a positive correlation between dermal and epidermal ascorbate (Supplementary Figure S1a–c). Skin ascorbate levels varied considerably but were not related to age, sex, or sun exposure (Supplementary Figure S2a–c).
Article Publication Date: 28/10/2025
DOI: 10.1016/j.jid.2025.10.587
