3.1 General Situation
As shown in TableⅠ, the average ages of the case group and the control group were 58.27 ± 8.01 and 58.43 ± 8.96 respectively. There was no difference between the two groups (P> 0.05), except for educational level (χ2= 41.693, P<0.001) and income (χ2= 31.372, P<0.001).
3.2 Comparison of Dietary Structure
According to the results of FFQ (TableⅡ), the intakes of livestock and poultry meat and milkin case group were higher than the recommended amount while the intakes of vegetables, fruits, eggs, and beans were lower than the recommended amount. Both groups seldom ate fish or shrimp. Although the intake of livestock and poultry meat and milk did not differ from each group, the two groups were statistically different in intake of the rest of the foods (P<0.05).
3.3 Comparison of Nutrient Intake
There was no difference in energy intake between the two groups (TableⅢ). The cholesterol intake of case group was higher than that of the control group while the intake of protein, vitamin A, thiamine, riboflavin, vitamin B6, FA, vitamin C, and vitamin E was lower than that of the control group and the difference was significant (P<0.05). According to the DRIs(3) recommended by the Chinese Nutrition Society for Chinese residents, the intake of thiamine, vitamin B6, vitamin E, and FA in both groups failed to reach 90% of the reference intake, and the FA intake of the case group did not reach 30% of the reference intake, which was severely inadequate.
3.4 Comparison of Serum Folic Acid, Vitamin B12 and DNMT1 Levels
Levels of serum FA and vitamin B12 in case group were significantly lower than those of the control group (TableⅣ)(z=-9.13, P<0.001; z=-6.06, P<0.001), whereas the serum DNMT1 level in case group was higher than that of the control group, and there was statistical significance (z = -5.37, P<0.001).
3.5 Logistic Regression Analysis of Risk Factors for Esophageal Cancer in Kazakhs
Multivariate binary logistic regression model was performed to analyze the influence of variables including education level, income, smoking, alcoholism, taste preference, vegetable and fruit intake, eating solid and hard food, eating quickly, dieting on time, eating smoked meat, serum folate level, serum vitamin B12 level and serum DNMT1 level (TableⅤ). The result showed that eating smoked meat was primary risk factor for ESCC(OR=12.812, 95%CI: 4.793-34.248), followed by serum DNMT1 level, alcoholism and eating solid and dry food (P < 0.05). By contrast, serum folate level was identified as the primary protective factor for ESCC(OR= 0.021, 95%CI: 0.004-0.101). Dieting on time and vegetable intake also played an important role in protective in ESCC happening (P < 0.05). Notably, the result demonstrated education level and income influenced the presence of ESCC as well (P < 0.05).
3.6 Relationship among Serum Folic Acid Level, DNMT1 level and Esophageal Cancer
Since the serum FA and serum DNMT1 levels in the case group were significantly different from those in the control group (P < 0.001), we further analyzed their relationships with ESCC. We divided serum FA level and DNMT1 level in the control group into four categories based on their quartiles (TableⅥ). The risk of getting ESCC in the second, third and fourth subgroup were 0.350, 0.167 and 0.150 times of that in the first subgroup respectively (χ2 = 15.281, 32.650, 34.642, P < 0.001).
As shown in TableⅦ, on the contrary, the risk of getting ESCC increased with serum DNMT1 level, though such tendency was only significant with serum DNMT1 level above 9.77ng/ml, In particular, the group with highest DNMT1 level above 9.77 underwent 4 times of the risk of ESCC compared to the group with lowest DNMT1 level(χ2 = 21.353, P < 0.001) but there was no significant relationships between ESCC and the group with serum DNMT1 level6.39~7.67ng / ml or the group with serum DNMT1 level 7.68 ~ 9.77ng / ml.