Eating two kiwifruit daily raised vitamin C levels in human skin and influenced key features of skin biology. Digest
Vitamin C supports collagen production and stress defenses, yet few studies directly measure how diet influences vitamin C inside living skin. A new study tackled this gap by tracking how increasing vitamin C intake from whole foods changes vitamin C levels inside different layers of human skin.
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The researchers worked with two cohorts. In the first cohort, they measured vitamin C in the dermis (the deeper, collagen-rich skin layer) and epidermis (the outer, cell-rich skin layer) from 38 adults undergoing elective surgery and related these values to fasting blood levels of vitamin C. In the second cohort, 24 adults completed an 8-week dietary intervention. These participants ate two SunGold kiwifruit daily (about 250 mg vitamin C/day), and the researchers compared blood and skin vitamin C levels before and after the intervention, alongside repeat tests of skin structure and function.
- The epidermis contained more vitamin C per gram of tissue than the dermis, but because the dermis makes up most of the skin's mass, whole-skin vitamin C levels mainly reflected dermal values.
- When vitamin C was estimated on a per-cell basis rather than per gram of tissue, dermal cells contained much more vitamin C than epidermal cells, which may help support collagen production in the dermis.
- Vitamin C levels in the skin were closely linked to vitamin C levels in the blood, especially in the epidermis.
- Eating kiwifruit increased blood vitamin C to a saturating range and raised vitamin C levels in skin samples.
- Participants who already had high blood vitamin C at the start showed little or no further increase in blood or skin vitamin C after the intervention.
- Higher blood vitamin C was associated with denser skin and more actively dividing cells in the outer skin layer, suggesting increased renewal activity. By contrast, skin elasticity changed only slightly, and the study did not detect changes in markers of ultraviolet light–induced stress or in biochemical indicators linked to new collagen production.
Because vitamin C enters skin cells through specialized transport systems, the close relationship between blood and skin vitamin C suggests that skin vitamin C levels are actively regulated, rather than passively diffusing from the bloodstream. Once inside the skin, higher vitamin C availability may help support collagen-building processes and healthy renewal of the outer skin layer.
The intervention was exploratory, with a small number of participants, no control group, and different skin-sampling methods, which limits how broadly the results can be applied. Even with these limitations, the study demonstrates that increasing vitamin C intake through food can raise vitamin C inside human skin and is accompanied by detectable biological changes. Our topic page on vitamin C provides a comprehensive guide to its roles in the body, including dietary sources and recommended intake levels.