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Introduction
Kimchi, a traditional fermented vegetable, is an indispensable component of every meal in Korea [1]. There are about 187 kinds of Kimchi according to the ingredients and processing methods [2]. Kimchi is prepared by various ingredients, such as Chinese cabbage, garlic, onion, and red pepper in the presence of salt [3]. Kimchi is currently recognized worldwide as a nutritious and healthy food. Nutritionally, Kimchi is a low-calorie food (18 kcal/100 g) and an important source of vitamins, minerals, and fiber [4]. It is also a good source of phytochemicals (e.g., β-sitosterol, glucosinolates, isothiocyanate, indoles, allyl compounds) and probiotic strains (e.g., Lactobacillus plantarum, Lactobacillus brevis, Leuconostoc mesenteroides) [5,6]. In regard to these nutrition properties, many functional properties of Kimchi have been reported including anti-oxidative activity [7,8], anti-mutagenic and anti-tumor activities [9], anti-atherogenic activity [10], and weight-controlling activity [11].
Immune system is very complex and a delicate network associated with the balance between health and disease. Any biologically active substances or food, which can enhance, suppress or modulate the immune system, is called an immunomodulator. Typical examples such as vitamins (A, C, E, B6), minerals (Zn, Fe, Se), probiotics and other foods (tomato, garlic, mushroom, soybean etc.) were explored [12].
Kimchi has been reported to have potential effects on the immune system [13]. Previous studies also reported that Kimchi has beneficial effects on stimulating the growth of spleen cells, bone marrow cells, thymus cells, and B cell proliferation in the spleen lymphocytes of rats [14]. Also, it is often believed that taking Kimch strengthen the immunity, and has been reported to decrease the risk of acquiring avian influenza (AI), severe acute respiratory syndrome (SARS) and flu.
To our knowledge, no published study has examined the effect of Kimchi consumption on the blood immune parameters in a clinical trial setting. Thus the present study was designed to determine assessed immunomodulatory properties of Kimchi consumption in the Chinese healthy college student.
Materials and Methods
Study design
This four-week clinical trial (randomized, open-labeled, prospective, and controlled) was carried out with healthy college students. The study was approved through the Institutional Review Board (IRB, KMC IRB1211-04) of Kyung Hee University Medical Center (Seoul, Korea).
Subjects
Recruitment was performed from July 2012 to September 2012, and the study was completed in November 2012. Forty-three healthy normal weight (BMI 18.5-23.0 kg/m2) Chinese college students over 20 years-old were enrolled in the study. Subjects suffering from any kind of disease/disorder, have a history of medication in the past few months were excluded. Subjects possessing any underlying conditions which might affect immunity and smokers were also excluded. All subjects were assessed for eligibility and provided written informed consent for participation in the study.
Randomization and intervention
Subjects were randomly assigned, using a computer-generated randomization sequence, into two groups, a Kimchi (n = 21, 100 g/day) or a non-Kimchi (n = 22, control) group. All eligible subjects were instructed to discontinue Kimchi and dishes made with Kimchi (e.g., Kimchi jjigae, Kimchi guk, Kimchi bokkeumbap, Kimchi bosaam) during one week of washout period.
At the beginning of the study, subjects underwent anthropometric and dietary assessment. A 24-hour dietary record (using food models) by a registered dietitian was used to examine nutrient intake. Nutrient intake was analyzed using the Computer Aided Nutritional Analysis version 4.0 (CAN-pro 4.0, The Korean Nutrition Society, Seoul, Korea). During the four-week intervention period, the Kimchi-group consumed 100 g of Kimchi/day and the non-Kimchi group consumed 100 g of radish/day.
Kimchi preparation
Kimchi, prepared with a standardized method by the Nonghyup Kimchi factory (Gyenggi, Korea) was provided every other day. The ingredients of Kimchi included 92.8 g cabbage preserved in salt, 1.4 g garlic, 2.1 g red pepper powder, 0.4 g ginger, 2.9 g onion, and 0.4 g salt.
Kimchi was fermented at room temperature then stored at 5℃ to 10℃ in a refrigerator until used. Fermentation was evaluated with a pH meter (Thermo Scientific, USA). The average pH of Kimchi was 4.2.
Blood analysis
Blood samples were drawn from the antecubital vein following an overnight fast (12-h) at the beginning and at the end of the study. Blood sample was obtained in ethylenediamine tetra-acetic acid-potassium (EDTA-K2) anticoagulant tubes and serum-separate tubes (SST). SST was immediately centrifuged (3,000 × g, 4℃, for 10 min) and the supernatant used for analysis.
White blood cell subsets (neutrophils, eosinophils, basophils, monocytes, and lymphocytes) were analyzed using flow cytometry by the Sysmes X-2,100 hematology analyzer (Sysmes, Kobe, Japan). Lymphocyte subset profiles were analyzed by flow cytometry (Beckman Coulter, USA). The absolute number and percentage of helper T cells (CD4+) and suppressor T cells (CD8+) were automatically calculated. Also, total T cells (CD3+), B cells (CD19+), and natural killer (NK) cells (CD16/56) were quantified using monoclonal antibodies against T cells, B cells, and NK cells, respectively. Antibody-bound cells were counted through flow cytometry using FACS can (Becton Dickinson, Franklin Lakes, NJ).
Serum total immunoglobulins (Ig A, G, and M) were measured using nephelometry by the Siemens Dimension Vista 500 automated analyzer according to the manufacturer's instructions (Siemens Healthcare Diagnostics Inc., Newark, DE, USA). Pro-inflammatory cytokines (IL-6, TNF-α) and anti-inflammatory cytokines (IL-4, IL-10) in serum were measured by the Luminex Multiplex Human High Sensitivity Cytokine Panel assay (Millipore, Billerica, USA). All assays were conducted according to the manufacturer's instructions.
Statistical analysis
Statistical analysis was performed using Statistical Package of Social Sciences (SPSS) version 20.0. The categorical variables of the two groups were compared with the Chi-square test, and the data presented as percentages or numbers. Continuous variables of two groups were compared with the independent or paired t-test, and data were presented as mean ± SD. The significance level was defined at p < 0.05.
Results
General characteristics
Among 43 healthy subjects two subjects from each group were withdrawn from the study due to personal reasons (moving a far distance away and taking medication). Thirty-nine students (20 in the Kimchi and 19 in the non-Kimchi groups) were able to finish the study. The average age of the subjects was 21.6 ± 2.1 years. The average height, weight, and BMI were 163.0 ± 6.4 cm, 54.9 ± 6.0 kg, and 20.6 ± 1.5 kg/m2, respectively. All subjects were in the normal range and no differences were observed between the groups.
Daily nutrition intake
The daily nutrient intake of both groups was compared with the Dietary Reference Intake for Koreans (KDRIs, 2010) (Figure 1). The average caloric intake was 80% of KDRIs and the intake of vitamins (B2, C) and minerals (Ca, K) were between 70 and 90% of KDRIs in both groups. There were no significant differences in the dietary intake of calories, proteins, vitamins, and minerals (except for Vitamin B6) between the groups during the study period.
White blood cell subset and immunoglobulin
The blood levels of white blood cell subsets (neutrophils, lymphocytes, monocytes) and immunoglobulins (Ig A, G, M) are given in Table 1. The levels of WBC subsets were not different between two groups at baseline and after 4 weeks. All values were in the reference range, neutrophils (50-80%), eosinophils (0-5%), basophils (0-2%), monocytes (2-10%), and lymphocytes (25-50%) [15].
The levels of Ig A and Ig G in the Kimchi group at baseline (194.6 ± 66.9 and 1207.1 ± 193.1 mg/dL) and after 4 weeks (194.1 ± 74.2 and 1173.5 ± 172.9 mg/dL) were significantly lower than the non-Kimchi group (baseline, 270.5 ± 74.5 and 1321.1 ± 105.2 mg/dL; after 4 weeks, 269.3 ± 75.5 and 1302.3 ± 132.9 mg/dL) (p < 0.05). These parameters were not significantly changed during the study period. Levels of Ig M were not different between two groups as well as between two periods.
Lymphocyte subsets
The levels (%) of lymphocyte subsets (T, B and NK cells) at baseline and after four weeks are given in Figure 2. Total T-cells and B-cells were not different between groups and was not significantly changed during the four weeks of intervention. Helper T cells at baseline and after four weeks in the Kimchi group (40.4 ± 6.5% and 40.8 ± 5.5%, respectively) were significantly higher than those of the non-Kimchi group (36.3 ± 5.5% and 35.8 ± 6.5%, respectively). NK cells at baseline and after four weeks in the Kimchi group (11.7 ± 2.8% and 10.6 ± 3.9%, respectively) were significantly lower than those in the non-Kimchi group (15.9 ± 7.0% and 14.7 ± 6.8%, respectively) (p < 0.05). These values were not significantly changed after four weeks of intervention in both experimental groups.
Suppressor T cells were not different between two groups at baseline. However, after four weeks, the level of suppressor T-cells were significantly increased in the non-Kimchi group (from 26.4 ± 5.5% to 28.8 ± 6.7%) but not in the Kimchi group (from 23.2 ± 5.2% to 26.5 ± 5.9%).
Pro- and anti-inflammatory cytokines
Blood levels of pro-inflammatory cytokines (TNF-α and IL-6) and anti-inflammatory cytokines (IL-4 and IL-10) are shown in Figure 3. The levels of TNF-α and IL-6 were not different between the groups; however values were significantly decreased in the Kimchi group (TNF-α; from 5.5 ± 1.7 to 4.7 ± 1.6 pg/mL, IL-6; from 0.5 ± 0.2 to 0.4 ± 0.2 pg/mL) and in the non-Kimchi group (TNF-α; from 5.3 ± 1.6 to 4.5 ± 1.6 pg/mL, IL-6; from 0.5 ± 0.2 to 0.4 ± 0.1 pg/mL) (p < 0.05).
The levels of anti-inflammatory cytokines, IL-4 and IL-10, in Kimchi and non-Kimchi groups were not significantly different. However, in the Kimchi group, the levels of IL-4 was significantly increased (from 0.7 ± 0.7 to 3.9 ± 5.7 pg/mL) however, IL-10 was not significantly changed (from 0.6 ± 0.4 to 0.5 ± 0.4 pg/mL).
Discussion
The present study was conducted to evaluate the potential immunomodulatory effects of Kimchi on selected immunological measure in healthy Chinese college students. Our findings indicated that there is no clear effect of Kimch intake on immune parameters, which is somewhat surprising. Because previous reports have suggested that various Kimchi ingredients (cabbage, garlic, onion, red pepper, and ginger) or probiotic strains improve immune markers both in vivo and in vitro studies, we hypothesized that fermented Kimchi exerts immunomodulatory effects.
Chinese cabbage, a main ingredient of Kimchi, is rich in minerals, vitamin C, dietary fibers, and especially phytochemicals [16]. Also, cabbage contains several organic sulfur compounds (OSCs), such as isothiocyanates and dithiolethiones. In a previous study [17], these OSCs were shown to exert diverse biological effects including the inhibition of tumor cell proliferation, antimicrobial effects, and free radical scavenging. Another ingredient, garlic, contains various sulfur-contained compounds; S-allyl-l-cysteine, S-allyl-l-cysteine sulfoxides and alliin [18]. It suppress the production of inflammatory cytokines, such as TNF-a, IL-1, IL-6, and interferon-γ [19]. Red pepper contains high levels (25-80 mg%) of capsaicin. Capsaicin (8-methyl-N-vanillyl-6-nonenamide) is involved in physiological functions related to immune response [20].
Probiotics are living micro-organisms that have a health benefit for their host. Orally ingested probiotic bacteria are able to modulate the immune system; however, differences exist in the immunomodulatory effects of different probiotic strains [21]. Especially, lactic acid bacteria (LAB) produced during the fermentation process from Kimchi : Leu. mesenteroides, Leu. citreum, Leu. gasicomitatum, Leu. kimchii, Leu. inhae, Weissella Koreensis, Weissella cibaria, Lac. plantarum, Lac. sakei, Lac. delbrueckii, Lac. buchneri, Lac. brevis, Lac. fermentum, Ped. acidilactici and Ped. Pentosaceus [22]. According to the Lee et al. [23], suppressor T cells and NK cells are increased with L. casei and Bifidobacterium longumi treatment. However, in present study, T-helper cells and suppressor T cells were not affected by the consumption of Kimchi. T cells play central roles in the immune system, in which their major function assisting B cells in the production of antibodies. Serum Ig levels are routinely measured in clinical practice to examine immune balance. Typical ranges are suggested (Ig A; 1.4-0.4 mg/mL, Ig G; 8-16 mg/mL, and Ig M; 0.5-2.0 ng/mL). Low levels of Ig were observed in humoral immunodeficiency, while high levels of Ig were observed in chronic inflammatory diseases. Until now, many studies showed that Kimchi inhibited Ig E levels in the NC/nga mice atopic animal model [24,25]. Also, lactobacillus plantarum isolated from Kimchi increased the production of Ig A in normal or S180-bearing BALB/C tumor-induced mouse [26,14]. On the other hand, 4 weeks of Kimchi supplementation does not changes of Ig A, G, M.
Cytokines, protein mediators produced by immune cells, are involved in immune regulation. The levels of pro-inflammatory cytokines are increased in chronic inflammatory diseases while the levels of anti-inflammatory cytokines are decreased. Kim et al. [11] showed that the consumption of fermented Kimchi (300 g/day for 4 weeks) had no effects on the levels of TNF-α and IL-6 in overweight and obese patients (22 subjects, mean age of 38.6 ± 8.5 years). In our study, the levels of TNF-α and IL-6 were significantly decreased in the Kimchi and non-Kimchi groups. It is unclear why the levels of pro-inflammatory cytokines in the non-Kimchi group were decreased.
In previous of clinical trials, anti-obesity, anti-hypertension, anti-hypercholesterol effects of Kimchi have been investigated however, their immunomodulatory effects are not reported. The strength of this study is that the effects of the Kimchi supplementation on blood immune parameters are examined. These study results are useful information in further research of the patients with dysregulated immune responses. On the other hand, small sample size and short duration may limit the power in detecting differences between groups. Further studies examining a various subjects with unbalanced immune system, larger samples for longer periods are necessary to determine the immune-modulation of fermented Kimchi. In addition, the decreased levels of TNF-α and IL-6 in placebo group may be due to the use of radish. Because nutritional intakes of the Kimchi and non-Kimchi groups during the 4 weeks of intervention were similar in this study, more research is need to interpret changes observed in the control group.
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