The skin protects the body from mechanical damage, microbial invasion, and radiation or UV light, as a barrier between the internal part of the body and the external environment. Thus, the skin plays an important role in the maintenance of homeostasis of the body by minimizing the moisture loss and regulating the temperature [1]. Also, the skin is the outermost protective layer of the body which is continuously exposed to external stimulants such as environmental pollutants or ozone, radiation, UV light, and thus has been greatly under stress due to oxidative damages. Reactive oxygens aggressive to the cells are continuously produced in the body while the life goes on and they become the main culprit of the cell aging [2,3]. Therefore, the roles of antioxidant for preventing the oxidation of skin cells have been concerned to maintain healthy and beautiful skin [4], and the development of products mainly applicable on the skin has been highlighted [5].

In the past, skin care and health management was treated by emphasizing skin troubles but in the present, the preventive program has come into the spotlight that integrates detailed skin analysis through skin care instruments, professional counseling, individualized care & treatment, and dietary habits & exercise lifestyle [6,7]. In case of Japanese women, Koyama et al. [8] reported that collagen peptide intake increased the absorption rate of water of stratum corneum. However, skin health-related domestic studies performed up to the present time are mostly about the influences of dietary habits and lifestyle on the skin [9-12]. Because problems related to skin health and skin condition can originate from the internal factors due to meals, it is necessary to study nutritional factors that affects skin condition. Thus, this study was performed to analyze the relationship between skin condition and antioxidant nutrition status and antioxidant activity through nutritional intake and biochemical analysis of the blood by skin type in female college students, and thus to utilize the study results as basic data in the skin care and health area.

This study was performed to investigate the antioxidant nutrition status by skin type through nutritional intake and serum analysis of antioxidant minerals and antioxidant enzymes by skin type in female college students. The dry skin group was 14% of all of 50 subjects, the mixed skin group was 56%, and the oily skin group was 30%. Compared to the study of Hong [12] (dry; 30%, normal; 50%, oily; 20%), the distribution of the dry skin group in this study was low and that of the oily skin group was rather high, and that of the mixed skin group was similar. The average age of the subjects was 20.5 ± 1.4 years, and the average BMI was 20.7 ± 2.0 kg/m², which was slightly lower than the average value for adults over 20s, 22 kg/m², presented by the KNS in 2005. Percent of body fat, WHR and soft lean mass were not significantly different by skin type. However, body fat mass in the mixed skin group was 16.8 ± 6.2 kg, which was higher than 15.3 ± 2.4 kg and 14.6 ± 3.1 kg in the dry skin group and the oily skin group, respectively, and slightly different from the result reported by Choi [15] in which higher BMI and body fat mass were observed in the oily skin group. When dividing the skin type by considering both hydration and sebum content, the difference in the sebum content was significantly observed in the T-zone between the dry skin group and oily skin group. Thus it is considered that the T-zone can represent the sebum content of the skin when measuring the sebum content only in particular areas. The average daily energy intake of the subjects was 2183.6 ± 507.7 kcal, which was about 104% of the recommended 2,100 kcal of the KDRIs (2005) [16] and no significant difference was observed among groups. Fat, cholesterol, saturated, and mono unsaturated fatty acid intake in the dry skin group was tended to be higher than in the mixed skin group and in the oily skin group. Park et al. [17] in the study for women in Gwangju region, reported that the fat intake was slightly lower in the oily skin group compared to the dry skin group. This suggests that individuals with dry skin might intentionally increase their fat intake. Cosgrove et al. [18] observed that higher intakes of linoleic acid were associated with better skin-aging appearance. The human skin is the most active organ among all tissues in the body and maintains the epidermal homeostasis by continuously forming new epidermal cells and repeating differentiation and exfoliation [19]. In particular, the lipid biosynthesis of the epidermis is the critical process of forming the skin barrier [20], and thus the importance of desirable fat intake has been emphasized as a fundamental way of managing dry skin. The CPF (Carbohydrate : Protein : Fat) ratio was 65 : 16 : 19, which is in the recommended range for adults over 20 years, 55~77 : 7~20 : 15~25. The fiber intake was 148% of the KDRIs(2005) [16] showing sufficient intake for dietary fiber. In case of zinc, the intake exceeded the recommended level in all three groups. The excessive intake of zinc interferes with the absorption of copper, possibly leading to copper deficiency and decreased HDL-cholesterol level, delayed would healing, skin dryness, and alopecia, and thus careful intake is needed [21]. The intakes of several vitamins were in the range of 130~180% of the recommended KDRIs (2005) [16], and the dry skin group showed rather higher intakes in vitamins except vitamin C than the mixed and oily skin groups, and significant differences were not observed among groups. The nutrients showing lower intake levels than recommended by the KDRIs (2005) were calcium (93%), potassium (72%), and folate (76%). In case of serum antioxidant enzymes, only the catalase content showed significant difference, with significantly higher content in the oily skin group than in the dry skin group and mixed skin groups (P < 0.05). SOD was 1.87 ± 0.63 U/mL in the oily skin group, which was higher than 1.57 ± 0.56 U/mL in the dry skin group. Superoxide anion (O^2-) is generated during the oxidative phosphorylation of the cell, particularly in large amounts during the lipid peroxidation, which damages the cell membrane [22]. Also, it has been reported that superoxide anion is activated to an uncoupling protein to increase the proton permeability, which is undesirable to cell metabolism [23]. There is a two-step mechanism in the body to eliminate superoxide anions. The first step involves SOD, in which O₂^- is converted to H₂O₂, and catalase metabolizes H₂O₂ into H₂O, in the antioxidant action. Thus, in relation to the result of this study that catalase and SOD contents were higher in the oily skin group with sufficient hydration and sebum contents, it is considered that the regulation of internal antioxidant defense mechanism can influence the health of the skin. Catalase is particularly decreased in the aging skin and thus presented as an antioxidant enzyme that has an important role in the skin aging process [24]. The concentration of malondialdehydes (MDA), a product of peroxidation showing the degree of serum lipid peroxidation due to oxidative stress, was 1.76 ± 0.63 µmol/L in the mixed skin group, which was significantly higher than 1.55 ± 0.23 µmol/L in the dry skin group and 1.47 ± 0.59 µmol/L in the oily skin group (P < 0.05). This is similar to the result reported by Bae [25] in which the average MDA concentration of women in 20s resided in Seoul was 1.63 ± 0.59 µmol/L, and also similar to the result by Han [26] in which the MDA concentration in the mixed skin was higher then those in the dry skin group and oily skin group. Dry skin is also known as xerosis, which appears as the moisture content in the stratum corneum is decreased, and if getting worse, the skin becomes weak and vulnerable to infection. The stratum corneum contains 10~20% of water from natural moisturizing factors, and if the moisture level becomes below 10%, the corneous tissue becomes thick and the skin texture becomes rough, and the aging accelerates. The extracellular lipids of the stratum corneum function as a water protection film, of which ceramide is over 40%, fatty acids is about 25%, and cholesterol is about 20%. Thus it has been known that if these three compositions change, then the function of protective film can be defected [27]. For possible influence of the difference in nutritional intake and dietary habit on the skin health, the correlation analysis between the hydration content of facial areas and dietary intake showed that a negative correlation was observed in the hydration of the cheek and zinc intake (r = -0.411, P < 0.01). Kim et al. [28] reported that skin evenness had negative correlations with zinc intake. Zinc has been known to protect the thiol group in the skin cell and thus to protect the skin cell membrane from oxidative damage by UV light, but excessive zinc intake for skin protection is not desirable for skin moisturizing. The correlation analysis among sebum content, serum antioxidant minerals and antioxidant enzymes, and MDA showed that a significant negative correlation was observed in the antioxidant enzyme GPx and the sebum content of the cheek (r = -0.292, P < 0.05). Sebum content of the cheek was decreased when serum GPx was high, and it is thus considered that lipid oxidation in the skin can be possibly prevented through complementary action with moisture. By combining the results that the hydration of the forehead and serum copper showed a significant negative correlation and the hydration of the cheek and serum zinc showed a significant negative correlation, and the results that the hydration of the forehead and GPx showed a significant positive correlation and the hydration of the chin and serum SOD also showed a significant positive correlation, it is thought that the activity of antioxidant enzymes rather than the serum mineral concentrations has positive influence on the hydration content of the fracial area. Therefore, if antioxidant enzymes such as GPx and SOD are used in cosmetics or functional foods, it can be possibly delay or prevent skin aging by maintaining the moisture level of the face. Skin health status appears to be affected by the interaction of the number of nutrients, not by single nutrient. By considering that the key concept of the quality of life recently is to provide sufficient nutrition from inside and outside the body to maintain skin health and beauty, it should be noted that the functions of nutrients as nutricosmeceuticals are being expanded. This study has a limitation in which the results came from a small number of subjects, and 1-day food intake record. Thus it is necessary to perform a large-scale study with lots of participants in the future to figure out the antioxidant defensive system of the skin that is possibly regulated by dietary changes.