**7.2 Bioavailability and absorption of vitamin C in the skin**

In order to perform its functions, ascorbic acid must be actively transported into the cell, a task performed by specific transporters present in the cell membrane.

In humans, two transporter families capable of transporting vitamin C have been described [14].


Sodium-dependent vitamin C transporters (SVTCs) are responsible for the absorption of vitamin C and its transport through the skin layers [14]. These two transporters are present in various tissues and organs.

SVCT1 is the main one in charge of transporting vitamin C at the epidermal level, while SVCT2 is in charge of taking vitamin C to the dermis, to transfer it, especially to the fibroblasts. From the dermis, vitamin C is transported to the epidermis where SVCT1 is responsible for providing ascorbic acid to the keratinocytes [15].

The specific location of SVCT1 in the epidermis is of great importance since it is an avascular layer and suggests that the combined expression of both transporters 1 and 2 ensures the effective absorption and intracellular accumulation of vitamin C and informs us of the high dependence on vitamin C of this tissue [13].

### **Figure 4.**

*Distribution of vitamin C in the skin mediated by SVCT1 and SVCT2. The black arrows indicate the transport from the dermis to the epidermis (avascular layer). Image taken from: https://commons.wikimedia.org/wiki/ File:Normal\_Epidermis\_and\_Dermis\_with\_Intradermal\_Nevus\_10x-cropped.JPG#filehistory. Kilbadderivative work: Fama Clamosa, Public domain, via Wikimedia Commons, and modified by the autor.*

SVCT1 has a low affinity for vitamin C but has a high transport capacity; in contrast, SVCT2 found in almost all cells of the body has a high affinity for vitamin C but a low transport capacity [16, 17].

It seems likely that, as occurs in other tissues, the levels of vitamin C in the skin respond to increases in its plasma concentration, especially with intakes that exceed the recommended daily amount. However, some authors suggest that skin levels do not increase once plasma saturation has been reached, so nutritional supplementation with vitamin C would be effective in raising skin vitamin C levels, only in people whose levels plasma are below the saturation point (**Figure 4**) [18].
